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MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) Expedition

Background    Research Vessel     Expedition Status   References

Embark on the largest polar expedition in history: in September 2019, the German research icebreaker Polarstern has set sail from Tromsø, Norway, to spend a year drifting through the Arctic Ocean - trapped in ice. The goal of the MOSAiC expedition is to take the closest look ever at the Arctic as the epicenter of global warming and to gain fundamental insights that are key to better understand global climate change. 1)

Hundreds of researchers from 19 countries take part in this exceptional endeavor. Following in the footsteps of Fridtjof Nansen's ground-breaking expedition with his wooden sailing ship Fram in 1893-1896, the MOSAiC expedition will bring a modern research icebreaker close to the north pole for a full year including for the first time in polar winter. The data gathered will be used by scientists around the globe to take climate research to a completely new level. Led by atmospheric scientist Markus Rex, and co-led by Klaus Dethloff and Matthew Shupe, MOSAiC is spearheaded by Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI).

Understanding the consequences of Arctic climate change:

• MOSAiC will contribute to a quantum leap in our understanding of the coupled Arctic climate system and its representation in global climate models.

• The focus of MOSAiC lies on direct in-situ observations of the climate processes that couple the atmosphere, ocean, sea ice, biogeochemistry, and ecosystem.

An entire year trapped in the ice

The Norwegian researcher and explorer Fridtjof Nansen set sail on the first ever drift expedition 126 years ago with his wooden sailing ship Fram. But there has never been an expedition like the one now planned: for the first time, the MOSAiC project will take a modern research icebreaker laden with scientific instruments close to the North Pole in winter. 2)

The backbone of MOSAiC will be the year-round operation of RV Polarstern, drifting with the sea ice across the central Arctic during the years 2019 to 2020. During the set-up phase, RV Polarstern will enter the Siberian sector of the Arctic in thin sea ice conditions in late summer.

A distributed regional network of observational sites will be set up on the sea ice in an area of up to ~50 km distance from RV Polarstern. The ship and the surrounding network will drift with the natural ice drift across the polar cap towards the Atlantic, while the sea ice thickens during winter (red dotted line in Figure 1).

Large scale research facilities addressing key aspects of the coupled Arctic climate system will be set up on board of RV Polarstern and on the sea ice next to it, in the so-called ice camp.

The distributed regional network further around the central observatory will be comprised of autonomous and remotely-operated sensors, characterizing the heterogeneity of key processes in an area representing a typical grid box of modern climate models and providing invaluable data for the development of parametrizations for sub-grid-scale processes in climate models.

The German research aircrafts Polar 5 and Polar 6 will be operated to complement the measurements at the central MOSAiC site. A landing strip will be built especially for these research planes and for resupply flights in spring 2020.

Research and supply cruises by icebreakers from MOSAiC partners will provide support for the AWI research vessel Polarstern. They will further extend the geographical coverage of the observations and will link the measurements to the larger scales of the Arctic climate system and explore global feedbacks.

In addition, helicopters will be employed. Fuel depots for long-range helicopters have been set up on Bolshevik Island to broaden the spectrum of response options to potential emergency situations during the expedition.


Figure 1: Not only the science behind MOSAiC is a huge endeavor that needs the expertise of multiple nations and scientific disciplines, but also the logistics face unparalleled challenges (image credit: AWI).

The mission of MOSAiC 3)

MOSAiC aims at a breakthrough in understanding the Arctic climate system and in its representation in global climate models. MOSAiC will provide a more robust scientific basis for policy decisions on climate change mitigation and adaptation and for setting up a framework for managing Arctic development sustainably.

The Arctic is the key area of global climate change, with warming rates exceeding twice the global average (Figure 2) and warming during winter even larger. It is well possible that the Arctic ocean will become ice free in summer during the 21st century. This dramatic change strongly affects weather and climate on the whole northern hemisphere and fuels rapid economic development in the Arctic.

Future climate change projections for the Arctic are extremely uncertain with a factor of three uncertainty of projected warming by the end of this century – a much larger uncertainty than anywhere else on the planet (Figure 3).

Many processes in the Arctic climate system are poorly represented in climate models because they are not sufficiently understood. As long as we do not understand these processes, Arctic climate projections will not be robust.

The understanding of Arctic climate processes is limited by a dramatic lack of observations in the central Arctic, especially in winter and spring. During these seasons sea ice is so thick that even the best research icebreakers cannot penetrate into the Arctic and researchers have always been locked out.

The dramatic changes in the Arctic climate system and the fast retreat of Arctic sea ice strongly affect global climate. The inability of modern climate models to reproduce Arctic climate change is one of the most pressing problems in understanding and predicting global climate change.

MOSAiC sets out to investigate the heart of the Arctic climate system year-round – one of the largest uncharted areas in climate research.


Figure 2: Near surface temperature changes 1970-2017 (graphic credit: NASA GISS,


Figure 3: For the Arctic the uncertainties of climate models are much larger than for any other part of the planet. Here projections of the warming by the end of the century range between 5º and 15º Celsius among the different models, for the same rather pessimistic greenhouse gas emission scenario (RCP8.5) which is shown here (graphic credit: AWI)

Some background

• September 24, 2019: As millions of people around the world marched for urgent action on climate change ahead of this week’s UN Climate Action Summit, an icebreaker set sail from Norway to spend a year drifting in the Arctic sea ice. This extraordinary expedition is set to make a step change in climate science – and ESA is contributing with a range of experiments. 4)

With the youth calling for action, the climate crisis is in the public eye more than ever, and consequently there is more pressure to push the issue higher up the global political agenda.

The state of the climate has been detailed in a new landmark report that was produced for the summit. It says that the five-year period from 2014 to 2019 is the warmest on record and that sea-level rise has accelerated significantly over the same period as carbon dioxide emissions have hit new highs.

Needless to say, a better scientific understanding of the complexities of the fragile Arctic environment is critical for policy decisions on climate-change mitigation and adaptation, and for setting up a framework for managing Arctic development sustainably. The EU’s Integrated Policy for the Arctic includes a central pillar of climate change for this reason.

The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition is about to make a major contribution to Arctic climate science.

Spearheaded by the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI), it is the biggest shipborne polar expedition of all time and aims to take climate research to a completely new level.

It involves the Polarstern German research icebreaker spending a year trapped and drifting in the sea ice so that scientists from around the world can study the Arctic as the epicentre of global warming and gain fundamental insights that are key to better understand global climate change.


Figure 4: The MOSAiC expedition will make a major contribution to Arctic climate science. Spearheaded by the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI), it is the biggest polar expedition of all time. It involves the Polarstern German research icebreaker spending a year trapped in the sea ice so that scientists from around the world can study the Arctic as the epicentre of global warming and gain fundamental insights that are key to better understand global climate change – and ESA is contributing with a range of experiments (image credit: AWI, S. Hendricks , CC BY-SA 3.0 IGO)

During each phase of this huge international expedition, roughly one hundred people will be researching, working and living on board the icebreaker as well as on the sea ice. They will face some extremely harsh conditions during the polar winter – complete darkness, storms and temperatures that can drop to –40ºC.

Christian Haas, from AWI, said, “We want to better understand the processes and energy flows between the ocean, ice and atmosphere – and how they change over the course of the seasons.

We will also compare the data with satellite data, in particular with ESA’s CryoSat-2, which was specifically launched to measure ice thickness. This will allow us to observe how the ice grows and becomes thinner.”

ESA’s Tânia Casal said, “The MOSAiC expedition offers a unique opportunity to considerably improve our understanding of ocean–ice-snow–atmosphere processes and this will contribute to a more accurate modelling of future Arctic climate scenarios.

“We want to make sure that data associated with these processes delivered by ESA satellites and by the Copernicus Sentinels as well as from missions under development have the best possible impact. So we are contributing to the expedition with a range of calibration and validation activities.

“For example, as Dr Haas mentions that arrangements have been made for measurements to be taken that will be used to validate CryoSat-2, but also that validate the Copernicus Sentinel-1 radar mission.”

ESA’s Craig Donlon added, “We are currently working on new high-priority missions such as the Copernicus Imaging Microwave Radiometer (CIMR) mission and the Polar Ice and Snow Topography Altimeter (CRISTAL) mission to support the EU Integrated Policy for the Arctic. CIMR will provide high-resolution multispectral images of ocean, ice and snow properties and CRISTAL will provide estimates of sea-ice thickness. The two missions can work in perfect synergy.

“MOSAiC will give us an unprecedented time series of reference measurements to develop quality algorithms and data products from the CIMR and CRISTAL missions, which will support applications from weather forecasting to climate research, with benefit for the Copernicus services and beyond.”

Dr Casal noted, “In addition, we are working with the Japan Aerospace Exploration Agency (JAXA) to collect measurements from the ALOS-2 mission as part of our preparatory work on the ROSE-L mission, which is another high-priority candidate for Europe’s Copernicus program, and which will work in synergy with the Copernicus Sentinel-1 C-band radar for sea-ice charting services.”

ESA experiments also include ship-based instrumentation for dedicated validation measurements of the thickness of thin seasonal ice from the Earth Explorer SMOS mission.

Josef Aschbacher, Director of ESA's Earth Observation Programs, said, “The scale of MOSAiC expedition is truly remarkable and a testament to what international collaboration can achieve. Climate change is a very serious global concern, and the pioneering satellite missions we develop are key to measuring and understanding change so that informed decisions on action can be taken. This expedition gives us an important and unique opportunity to validate measurements being made from space as well as further the development of new missions on the drawing board. We wish everyone participating in MOSAiC the very best of luck – it will certainly be a challenging and harsh environment to work in.”


Figure 5: Sea-ice drift. In October 2019 the research icebreaker Polarstern will drop anchor at an ice floe in the northern Laptev Sea, which will mark the beginning of the MOSAiC experiment. The ship’s potential drift route can be roughly estimated in advance by reconstructing the course that the ice followed from the starting point in past years. This involves the use of satellite data, which depicts the ice drift in the Arctic on a daily basis. The image shows sample drift trajectories for 2005–17 and a potential starting point near 85ºN/130ºE. The starting date for the drift analysis is always 1 October of the respective year (image credit: AWI)

• September 20, 2019: During the MOSAiC expedition, researchers from the DLR Institute of Communications and Navigation will be measuring the disturbances of the Galileo and GPS navigation signals near the pole over a long period. “For this purpose, we have installed a high-rate receiver for navigation satellite data, one of our ‘in-house’ processors for measuring scintillations and a recording device for the raw data on board Polarstern,” says Simon Plass from the DLR Institute of Communications and Navigation. Scintillations are fluctuations of the electron density in Earth’s ionosphere. They influence the propagation of electromagnetic radiation; this includes the signals from navigation satellites. 5)

- Particularly in the vicinity of the north and south poles, the signals from navigation satellites are subject to disturbances caused by solar activity. No real data are currently available for the development of suitable countermeasures.

- DLR is closing this gap by collecting the necessary raw data from the Galileo and GPS systems in the Arctic Ocean during the one-year-long MOSAiC polar expedition. They will then be used to develop processing and correction algorithms.

- In the harsh environment of the Arctic Ocean, it is particularly important that position determination is always precise, and that safe navigation can be guaranteed.

The team of Simon Plass will operate the processor together with colleagues from the newly founded DLR Institute for Solar-Terrestrial Physics. “This is the first time that we will have acquired such extensive data from the north polar region. They represent a unique opportunity to compare the performance of different receivers under identical, controlled conditions and to develop new signal processing algorithms,” explains Plass.

The solar storm particles influence the functioning and accuracy of communications and navigation systems – particularly near Earth’s poles.

The explosive eruptions of charged particles from the surface of the Sun are referred to as solar flares. They are a cause of ‘space weather’ and the particles regularly interact with Earth’s magnetic field. The nearer one gets to the poles, the stronger the interactions become. Two of the best-known effects are the Aurora Borealis and the Aurora Australis, fascinating natural spectacles that make the influence of the Sun on the northern and southern polar regions visible to the human eye.

Charged particles from the Sun interact with Earth’s atmosphere and cause scintillations in the ionosphere. This interferes with radio signals on their way from satellites to the planet’s surface. Navigation signals in particular can be influenced to such an extent that precise positioning is sometimes no longer possible. In order to develop effective countermeasures, such as correction algorithms for navigation systems, satellite data from the polar regions are required. These data are currently not available.


Figure 6: Infographic: Charged particles from the Sun interact with Earth’s atmosphere and cause scintillations in the ionosphere. This interferes with radio signals on their way from satellites to the planet’s surface. Navigation signals in particular can be influenced to such an extent that precise positioning is sometimes no longer possible. In order to develop effective countermeasures, such as correction algorithms for navigation systems, satellite data from the polar regions are required. These data are currently not available (graphic credit: DLR (CC-BY 3.0))

Other DLR participants in the MOSAiC Arctic expedition: In addition to the Institute of Communications and Navigation, two other DLR facilities are taking part in MOSAiC. During the expedition, the German Remote Sensing Data Center (DFD) will be providing images derived from data acquired by the German TerraSAR-X radar mission in near-real time to support the complex expedition logistics in the sea ice. In addition to DFD’s own receiving stations in Neustrelitz and Inuvik, Canada, the Kongsberg Satellite Services (KSAT) station near Longyearbyen on Spitsbergen will also be used to receive data from the satellite. This station network is suitable for making the satellite data collected over the Arctic Ocean available to the researchers on board Polarstern as soon as possible after acquisition. The data are first transmitted from the receiving stations to Neustrelitz for processing and then delivered from there.

In addition to TerraSAR-X, other radar satellites will be used for MOSAiC, such as the Canadian RADARSAT-2 and the Japanese ALOS-2. The DLR Maritime Safety and Security Lab in Bremen will be responsible for the coordination of all the satellite images and the timing of further experiments or aircraft measurements. Together with the University of Bremen, it will also use the MOSAiC mission to improve the methodology developed at DLR for distinguishing between different types of ice and to derive further properties of snow and ice cover from satellite signals in the microwave frequency range. This research is part of a separate project, 'MOSAiCmicrowaveRS', funded by the German Research Foundation (DFG). In addition to the satellite data, it will use the extensive measurement facilities on the Polarstern.

RV (Research Vessel) Polarstern

For one year, she will be the center of the largest Arctic research expedition ever, spending a full annual cycle trapped in the massive Arctic ice: the Research Vessel Polarstern, flagship of Alfred Wegener Institute and icon of German as well as international Polar Research. 6)

Originally commissioned in 1982, the Polarstern is, to this day, still one of the most advanced and versatile polar research ships worldwide. Between 1999 and 2001, the ship was completely overhauled and now carries the latest equipment and technologies available. This is why she usually operates 317 days on average every year. Covering about 50,000 nautical miles per year, Polarstern carries out scientific research as well as resupplies the research stations run by the AWI (Alfred Wegener Institute) - such as the Neumayer Station III, an Antarctic base manned year-round. Until 2019, Polarstern has logged more than 1.7 million nautical miles, which equates to roughly 3.2 million km.


Figure 7: Photo of RV Polarstern (image credit: AWI)

The Polarstern and MOSAiC:

Even for the reliable Polarstern and her highly experienced crew, the MOSAiC expedition poses quite a challenge. Only thanks to her special technical details, this ship can be the center of an expedition with the dimensions of MOSAiC. Not only is Polarstern capable of operating in the pack-ice zone, but owing to her double-walled steel hull and 20,000 horsepower, she can also easily break through 1.5-meter-thick ice and overcome thicker ice by ramming. Being equipped for sustained operations at temperatures like in the Arctic winter, down to -50º Celsius, Polarstern is also capable of staying the winter in the ice of the polar seas.

However, it’s not nearly so cold inside the ship, where the about 100 MOSAiC researchers, technicians and crew members work and live. In the various scientific labs, the international experts conduct research across the 5 main areas of interest ( atmosphere, ocean, sea ice, ecosystem, biogeochemistry). For MOSAiC, this set-up will be complemented with specific scientific equipment, instruments and lab containers, and even a special additional crane has been installed.

In addition, Polarstern has various vehicles (helicopters, snowmobiles, Pistenbullies, etc.) on board, allowing the researchers to take measurements and gather data not only in the central observatory but also in the distant Distributed Network. The cutting-edge onboard computer system ensures that all scientific data are regularly recorded, saved and forwarded.

Port of Registry


Length, Width, Max. draught (draft)

118 m, 25 m, 11.2 m

Max. displacement, Empty weight,

17,277 tons, 12,012 tons

Commissioning, Engine

1982 (AWI), 4 x KHD RBV 8M540

Enging power, Range

19198 HP (four engines), 19000 nautical miles / 80 days

Max speed, Operation area

16 knots, Everywhere including pack ice zone

Crew, Days on sea per year (2018)

44, 317


Nobiskrug, Rendsburg and Howaldswerke - Deutsche Werft Kiel AG, Germany

Participants per day / long term sailing

none / 53

Table 1: Facts and figures of the RV Polarstern

MOSAiC Expedition status and documentation

• 07 February 2022: Hundreds of international researchers are currently analyzing observations from the one-year MOSAiC expedition, during which hundreds of environmental parameters were recorded with unprecedented accuracy and frequency over a full annual cycle in the Central Arctic Ocean. They have now published three overview articles on the MOSAiC atmosphere, snow and sea ice, and ocean programs in the journal Elementa, highlighting the importance of examining all components of the climate system together. These results present the first complete picture of the climate processes in the central Arctic which is warming more than two times as fast as the rest of the planet - processes which affect weather and climate worldwide. 7)

- Diminishing sea ice is a symbol of ongoing global warming: in the Arctic, its extent has almost halved in summer since satellite records began in the 1980s. Less well studied but equally relevant are the thickness and other properties of the ice. The question of what this means for the future Arctic and how these changes will affect the global climate were the impetus for the historic MOSAiC expedition with the German research icebreaker Polarstern from September 2019 to October 2020. With these results coming out now the researchers are building the most complete observation-based picture of climate processes in the Arctic, where the surface air temperature has been rising more than two times as fast as on the rest of the planet since the 1970s. To study the relevant processes for a full year required a special concept, in part because the Central Arctic Ocean is still ice-covered in winter and therefore difficult to access. During the expedition, the icebreaker froze to a large ice floe and drifted with the natural transpolar drift across the Arctic Ocean. And this is where the first surprises came. "We found more dynamic and faster drifting pack ice than expected. This not only challenged the teams on the ground in their daily work, but above all resulted in changed sea-ice properties and sea-ice thickness distributions," reports Dr Marcel Nicolaus, sea-ice physicist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and co-leader of Team Ice in the MOSAiC project.

- One of the reasons for the rapid drift is provided by the analysis of the atmospheric research team: "Near the surface there were particularly low temperatures and associated persistent strong winds in the winter months that pushed Polarstern faster than expected. Large-scale atmospheric pressure and wind patterns in January to March led to a particularly strong polar vortex around the Arctic, in addition to a record ozone hole in the Arctic stratosphere," explains Dr Matthew Shupe, atmospheric scientist at CIRES (Cooperative Institute for Research in Environmental Sciences) at the University of Colorado and NOAA and co-leader of Team Atmosphere.


Figure 8: Drift tracks of the central observatories (CO) of MOSAiC in 2019–2020 (Graphic: MOSAiC Team Ice, Marcel Nicolaus)

- The oceanography team is analysing how atmosphere and sea ice changes are related to the water temperature and salinity. "We observe an increasing connection between the upper ocean and the deeper warm water layers in the Central Arctic Ocean, year-round," reports Dr Céline Heuzé, physical oceanographer at the University of Gothenburg and co-leader of the MOSAiC Team Ocean. "We were able to fully map ocean eddies over a complete annual cycle during the expedition. Nearly simultaneous measurements from Polarstern, our camp set up next to it on the ice and the distributed network up to 50 km away from the ship provide the first assessment of small-scale events up to the regional scale," adds Dr Benjamin Rabe, co-leader of the MOSAiC Team Ocean and physical oceanographer at the AWI.


Figure 9: The terrestrial laser scanner (TLS) creates 3D laser scans of the land-/snowscape on the MOSAiC ice floe. The scans allow investigating changes in ice and snow conditions by measuring e.g. wind driven height changes of the snow or ridge formation of the ice (photo credit: Matthias Jaggi)

- Autonomous sensors were mounted on, in and under the ice to provide coordinated measurements of properties like temperature, winds or currents in the atmosphere, in the sea ice and down to several hundred metres in the ocean below. Atmospheric winds push the ice and cause snow to drift. The researchers investigated in detail how the winds affect the sea ice, for example, by recording the tension in the ice and measuring cracks and the height of the rising ice ridges. These properties in turn influence where and how snow is deposited or swept away. Snow stands out for its extreme physical properties, as it insulates the sea ice against the atmosphere, reflects most of the sun light and contains of fresh water.

- "We were able to show how short-term atmospheric events (storms in winter, warm spells in spring, meltwater fluxes in summer or rainfall in autumn) have large effects on the snow and sea-ice properties over the coming months," Marcel Nicolaus describes the current findings. "We found larger spatial variations in the snow cover than expected, due to atmospheric processes and the structure of the underlying sea ice. This extreme variability means that we have to consider the snow in much more detail for future model simulations and the interpretation of satellite observations. As we have also been able to make remote sensing measurements on the ice, these - combined with the detailed snow and ice observations - pave the way for new and improved sea-ice observations from upcoming satellite missions. In addition, this enables a better uncertainty assessment of existing satellite time series," the AWI sea-ice physicist continues.


Figure 10: The two Atmos Flux sleds were the first instruments place on our floe. Moving these flux sleds are always a challenge. A team of MOSAiC participants came together to push the sled to a desirable site. There were a few obstacles on the way, such as the large ridge bordering the Logistics area, melt ponds, and drainage channels on the ice (photo credit: Lianna Nixon)

- Atmospheric scientist Matthew Shupe adds: "During MOSAiC, we observed more than 20 Arctic cyclones, or storms, of various scales that passed over our ice floe. We have described these events in unprecedented detail, characterising the vertical wind structure and momentum transfer to the sea ice and ocean, leading to sea-ice movement and fracture. During these events, the impacts of warm air masses moving into the Central Arctic with their associated clouds caused significant shifts in all components of the surface energy balance, affecting the sea-ice temperature, growth, and/or melt. Additionally, year-round information on the variability of atmospheric composition and aerosols provides new insights into the relative influences of long-range transport versus local processes, with important implications for climate-relevant cycles (e.g. the carbon cycle), clouds, and the radiative balance."


Figure 11: Markus Rex (r), Matthew Shupe (l) and Marcel Nicolaus front of Polarstern on the ice floe. October 9, 2019 (photo credit: Esther Horvath, Alfred-Wegener-Institut, Helmhol)

- The three overview articles serve as references for a vast array of future scientific work. "The physical observations are the basis for interpreting biogeochemical cycles and ecosystem processes, and for supporting coupled models that we use to learn even more about climate feedbacks and the global repercussions of Arctic change. These changes can affect weather and climate worldwide," says Prof. Markus Rex, head of MOSAiC and atmospheric scientist at the AWI. "It is fascinating how accurately we can map individual processes and relate them to each other. I am pleased to see how several hundred MOSAiC participants have collaborated on these publications. International cooperation with expedition participants from so many countries continues productively in a highly coordinated manner, even though the expedition has been over for more than a year. In this way, we will be able to provide ever more important insights into climate change, which will provide a knowledge base for societal transformation towards a sustainable approach to planet Earth," says MOSAiC leader Markus Rex.

Background information on MOSAiC

- During the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, experts from 20 nations explored the Arctic for an entire year. From autumn 2019 to autumn 2020, the German research icebreaker Polarstern drifted frozen in the ice through the Arctic Ocean. MOSAiC was coordinated by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). In order to make this unique project a success and to obtain the most valuable data possible, more than 80 institutes had pooled their resources in a research consortium. The total cost of the expedition was about 150 million euros, mostly funded by the German Federal Ministry of Education and Research.


Figure 12: Crack through our Logistics area and far beyond (photo credit: Christian Rohleder)

Figure 13: Deep Insights Into the Arctic of Tomorrow. Two years ago, hundreds of international scientists set off on the one-year MOSAiC expedition, collecting unprecedented environmental datasets over a full annual cycle in the Central Arctic Ocean. Now, The team has published three overview articles on the MOSAiC atmosphere, snow and sea ice, and ocean in the journal Elementa, highlighting the importance of examining all components of the climate system together. These results present the most complete picture of the climate processes in the Central Arctic which is warming more than two times as fast as the rest of the planet - processes that affect weather and climate worldwide (video credit: CIRES)

Publications 8) 9) 10)

• 23 June 2021: Results of the MOSAiC expedition show: the expected recovery of the ozone layer may fail to happen anytime soon, if global warming is not slowed down. 11)

- In spring 2020, the MOSAiC expedition documented an unparalleled loss of ozone in the Arctic stratosphere. As an evaluation of meteorological data and model-based simulations by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) now indicates, ozone depletion in the Arctic polar vortex could intensify by the end of the century unless global greenhouse gases are rapidly and systematically reduced. In the future, this could also mean more UV radiation exposure in Europe, North America and Asia when parts of the polar vortex drift south. With their new findings, the experts call into question the commonly held assumption that, thanks to the ban on the production of chlorofluorocarbons (CFCs), ozone loss would grind to a halt in just a few decades. The AWI study was jointly conducted with the University of Maryland and the Finnish Meteorological Institute, and has now been published online in the science magazine Nature Communications. 12)

- On 12 October 2020, when Polarstern returned to Bremerhaven from MOSAiC – the largest Arctic expedition in history – she brought with her troubling news: broad expanses of open water to the north of Greenland, and sea ice riddled with meltwater pools at the North Pole, bore witness to the dramatic effects of global warming that could already be seen in the Arctic. But the rapid melting wasn’t the only thing that worried Expedition Leader Markus Rex: “Readings taken during the expedition showed that the chemical loss of ozone over the Arctic in the spring of 2020 was worse than ever before. A comprehensive analysis has now determined that this was also due to climate change. Unfortunately, our work indicates that, if climate change continues unchecked, loss of ozone over the Arctic will likely continue to worsen through the end of the 21st century, despite the global ban on ozone-destroying substances.” During MOSAiC, at the altitude range of maximum ozone concentration, approx. 95% of the ozone had been destroyed. As a result, the thickness of the ozone layer was reduced by more than half, even though the concentration of ozone-destroying substances has declined since the turn of the millennium – a success of the international efforts to protect the ozone layer.

- Does that mean the ozone layer – a protective barrier against harmful UV radiation – over the Arctic is increasingly at risk?

- To find the answer, a team led by the AWI experts Peter von der Gathen and Markus Rex, and by Ross Salawitch from the University of Maryland, compared the data from 53 computer models created in the context of the international “Coupled Model Intercomparison Project Phases 5 and 6” (CMIP5, CMIP6). Working from this basis, the researchers then projected the ozone depletion in the Arctic polar vortex up to the year 2100. The vortex, a relatively self-contained low-pressure system in the stratosphere at an altitude of 15 to 50 km, forms over the Arctic every autumn and stays for varying durations throughout winter and spring. “For ozone to be depleted in the Arctic, the stratosphere must cool down considerably at the altitude where the ozone layer is,” says Peter von der Gathen, first author of the study. “Chlorine, which is normally bound in harmless substances, is released at low temperatures. Subsequently, chlorine together with bromine destroy ozone when exposed to sunlight. However, this only takes place when temperatures sink low enough during winter. Accordingly, in our study we estimated the ozone loss in the next few decades on the basis of the long-term temperature trend in the polar vortex and the expected decline in chlorine and bromine compounds.”


Figure 14: Ozone content on 29 March 2020 above the Arctic in about 20 km altitude, as calculated by the ATLAS model of AWI. On that day and at this altitude, ozone disappeared almost completely inside the polar vortex. Usually, in this altitude range most of the Arctic ozone can be found. 2020 had been the year with the strongest ozone loss in the Arctic until now (image credit: Peter von der Gathen)

- Despite the production ban issued in the 1987 Montreal Protocol, substances like chlorofluorocarbons (CFCs) and halons, which contain ozone-destroying chlorine and bromine atoms, are still abundant in the atmosphere, because they break down only very slowly. “The concentrations of these substances in the polar vortex continued to rise until the year 2000,” says Peter von der Gathen. “Since then, they’ve been on decline and are currently at roughly 90 percent of the maximum. Only by the end of the century they will have fallen below 50 percent, according to an assessment of the World Meteorological Organization. Since the pattern of warm and cold stratospheric winters in the polar vortex is very irregular, the degree of ozone depletion varies accordingly. Superimposed on this, however, our analysis of meteorological data from the past 56 years shows a significant trend toward lower temperatures in the cold stratospheric winters and associated increases in ozone losses. In addition, the analysis of the climate models clearly shows that this trend is part of climate change and therefore the product of global greenhouse-gas emissions.”

- The complex underlying mechanism is at least partly understood: the same gases that result in global warming at the Earth’s surface (like CO2) also promote cooling of higher atmospheric layers in the stratosphere, where the ozone layer is located. “In addition, due to climate change we notice changes in the prevailing wind systems. We suppose that these changes also contribute to lower temperatures in the polar vortex. Up to now, the trend towards colder winters in the Arctic stratosphere was debated among researchers. Even when assuming such a trend it was believed that climate change would, in the worst case, prolong the recurring ozone depletion over the Arctic by a few years,” Peter von der Gathen explains. “By then at the latest – that’s what we assumed, too – the falling concentrations of CFCs would become such a dominating factor that the ozone loss would continually fade. But, according to our new calculations, things could also turn out very differently in the Arctic.”

- The team’s analysis shows that the future chemical loss of ozone in the Arctic will greatly depend on the amount of greenhouse gases emitted by the end of the century. If emissions are substantially reduced in the coming decades, the study actually predicts an early and then steady decline in the degree of ozone loss; but for less optimistic scenarios characterized by rising greenhouse-gas emissions, the opposite could happen. “If we don’t reduce our greenhouse-gas emissions rapidly and decisively, loss of ozone in the Arctic stratosphere could, despite the great success of the Montreal Protocol, continue to worsen through the end of this century, instead of following the generally expected path towards a full recovery of the ozone layer” explains Markus Rex. “This represents a fundamental paradigm shift in our assessment of the future of the Arctic ozone layer. And the future of the Arctic ozone layer is relevant for life in Europe, North America and Asia: the Arctic polar vortex occasionally drifts south, which can lead to a few days with a reduced ozone layer over populated areas in spring, increasing levels of UV radiation and ultimately a greater risk of sunburn and acquiring skin cancer during these periods.”

- For Markus Rex, the message from the Arctic is clear: “There are plenty of good reasons to quickly and comprehensively reduce greenhouse-gas emissions. Now we can add the risk of intensified ozone depletion over the Arctic to the list.”

• 12 October 2020: Welcome home! The Polarstern is back in its home port of Bremerhaven. Today a record -breaking expedition ends: never before had an icebreaker ventured so far north during the arctic winter, and never before could international researchers comprehensively gather such urgently needed climate data in the region of the world hardest hit by climate change. 13)

- Drifting with the ice, they endured the extreme cold, Arctic storms, a constantly changing floe. ”With the MOSAiC expedition, we have followed in the footsteps of the Norwegian polar researcher Fridtjof Nansen, who ventured the first ice drift through the Arctic Ocean more than 125 years ago” says Antje Boetius, director of the Alfred Wegener Institute. ”And even with the possibilities of modern polar research, the expedition was no less exciting, taking us far beyond the limits of our previous understanding, and demanding a great deal from the participants, especially due to the pandemic.”

- Expedition leader Markus Rex says: ”I'm very pleased with how the MOSAiC expedition progressed, and what a complete success it has been. Through the expedition, we can provide the climate data and observations that humanity so urgently needs in order to make fundamental and pressing political decisions on climate protection.”

- But the work is not finished with the arrival of the ship, on the contrary: now begins the evaluation of the vast amount of data that had been collected over the past few months. The research teams who had been working on the ice and the ship in the Arctic all the time were not yet able to properly at their data. This will now be processed in the coming months and years and will greatly expand our understanding of the Arctic, and with the effects of climate change, which threatens not only this unique region, but the whole world. 14)


Figure 15: Accompanied by numerous ships and boats, the Polarstern arrives in Bremerhaven with the participants of the MOSAiC expedition. After 389 days in the Arctic, the biggest Arctic expedition of all time ends (image credit: Joachim Hofmann)


Figure 16: Officially, the participants were received by the Federal Minister of Research, the head of AWI and the two mayors of Bremerhaven and Bremen. From left the right: Captain Thomas Wunderlich, MOSAiC expedition leader Prof. Dr. Markus Rex (AWI), Federal Research Minister Anja Karliczek, AWI Director Prof. Dr. Antje Boetius,, Bremerhaven Mayor Melf Grantz and Bremen Mayor Andreas Bovenschulte (photo credit: AWI, Kerstin Rolfes, Ref. 14)


Figure 17: Overview of the Polarstern travel route, drifting in the Arctic sea ice (blue), and shipping in the Arctic Ocean (image credit: MOSAiC Expedition, AWI)

• 09 September 2020: On 19 August 2020, the world’s largest and longest polar research expedition – known as MOSAiC – reached the North Pole after making an unplanned detour owing to lighter-than-usual sea ice conditions. The expedition is now entering its final stage, during which researchers will study the last piece of the Arctic puzzle: the growth of new sea ice marking the end of the summer season. 15)

- In September 2019, the German research icebreaker Polarstern set sail from Tromsø, Norway, to spend a year drifting through the Arctic Ocean – trapped in ice. After leaving the ice floe it had been sitting in for the previous ten months, the icebreaker travelled through the Fram Strait and along the northeast coast of Greenland – a region that is usually home to thick, multi-year ice.

- Using radar satellite imagery and sea-ice data, researchers onboard the vessel determined that the ice conditions this year were ‘lighter than usual’ and were able to complete their journey to the North Pole in just six days.


Figure 18: The MOSAIC expedition will make a major contribution to Arctic climate science. Spearheaded by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), it is the biggest polar expedition of all time. It involves the Polarstern German research icebreaker spending a year trapped in the sea ice so that scientists from around the world can study the Arctic as the epicenter of global warming and gain fundamental insights that are key to better understand global climate change – and ESA is contributing with a range of experiments (image credit: MOSAIC)

- Onboard, during the year-long experiment, around 600 researchers from 20 countries have been carrying out various experiments on the sea ice surrounding the ship in order to gain fundamental insights that are key to better understand global climate change.

- Tânia Casal, scientific campaign coordinator for MOSAiC, explains, “The vital importance of these measurements is related to the fact that they are made continuously and simultaneously throughout the full year. The data acquired will give the scientific community an exceptional dataset that will be studied for years to come.”

- One of ESA’s experiments includes the use of a new ground-based dual frequency radar which has been used to measure sea-ice of a different age and thickness and is also able to distinguish between the snow and ice among the first results.

- Tânia comments, “Even though the conditions on the ice have been quite challenging due to the unusual weather conditions faced this year, first results have already revealed that warming events and associated changes of the snow surface can lead to an underestimation of the ice concentration – a major variable when studying the Arctic conditions.”

- Understanding snow and measuring snow depth is very relevant also for ESA’s CryoSat and SMOS missions, as well as preparing for the next three Copernicus high priority candidate missions: CIMR, CRISTAL and ROSE-L.


Figure 19: This image shows the Arctic sea ice conditions north of Greenland captured by the Copernicus Sentinel-1 mission on 14 August 2020 (image credit: ESA, The image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)

- Now that the Polarstern has reached the North Pole, researchers have picked out a new ice floe to attach to in order to observe and study the re-freezing of melt ponds and the start of autumn freezing of sea ice.

- Normally, the North Pole is not usually covered by satellite data, and therefore leaves what is called a ‘pole hole’ visible in most Arctic maps. Ordinarily, vessels do not journey near the North Pole, so ice support services are not warranted or needed.

- This posed a challenge during the MOSAiC expedition when the Polarstern ship drifted north of the Copernicus Sentinel-1 routine coverage to continuously study the development of the sea ice. In order to get around this, the WMO Polar Space Task Group (PSTG), which comprises 13 Space Agencies, has undertaken a special tasking of satellites to obtain data of the seldom imaged North Pole region.

Figure 20: This animation shows the Arctic sea ice extent from 1 September 2019 until 31 August 2020. The circle in the middle indicates a lack of data, what is often referred to as a ‘pole hole’ and is visible in most Arctic maps (video credit: JAXA/University of Bremen/ESA)

- This involved obtaining observations from CSA RADARSAT-2 and RADARSAT Constellation Missions, DLR’s TerraSAR-X and ASI’s COSMO-SkyMed mission. ESA’s Mark Drinkwater says, “The Polar Space Task Group has made a very special effort in the name of MOSAiC and the Year of Polar Prediction science to collect data in a location where normally there is none.”

- Depending on ice and weather conditions, the Polarstern will follow the Transpolar Drift southwards, from its current position at 88° North. The Polarstern is expected to complete the final stage of the experiment and return to Bremerhaven, Germany, by mid-October.

• 31 July 2020: After exactly 300 days of drifting with the MOSAiC floe, the international team around Expedition Leader Markus Rex on Wednesday, 29 July 2020, started the dismantling of the research camp and evacuation of the floe. Just one day later the floe finally broke into several fragments. After accompanying the floe on its journey for ten months, the team will now shift its focus to the last remaining puzzle piece in the annual cycle of Arctic sea ice: the start of the ice formation process. 16)

- It came as expected: with a loud bang, on 30 July the MOSAiC floe broke into several fragments, which will drift out to the open ocean of Fram Strait within the next few days. Momentarily, the floe fragments are five kilometers apart from the ice edge. But the experts’ timing was flawless: they continued their work with the complete research camp until the very end, before efficiently dismantling it and bringing all their equipment back on board, all within a day. Thereby it was possible to also document the very last phase of the life of the MOSAiC floe as planned - an impressive success for the expedition.

- “We’ve successfully monitored the lifecycle of the MOSAiC floe from early October last year to its end. It carried us through the Arctic Ocean for a total of 1700 km, from the Laptev Sea, past the North Pole and all the way to Fram Strait. Here at the sea-ice edge its natural lifecycle comes to an end: the fragments will continue to grow thinner and be broken up by waves, until they ultimately melt and once again become part of the seawater, from which the floe was formed nearly two years ago off the Siberian coast. Accordingly, the concept for the expedition has been completely fulfilled,” says Expedition Leader Prof Markus Rex from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research. “Now we’ll focus on the last piece of the puzzle in the annual cycle: the start of freezing at the end of the summer. For this phase we’ll be heading farther north, where the ice formation will soon begin.”


Figure 21: Packing up instruments in Met City, which is situated directly next to a melt pond (photo credit: Lianna Nixon)

- Initially, however, the Polarstern will remain near the ice edge, until the Russian research icebreaker Akademik Tryoshnikov joins her in the near future. The latter ship will bring with her the research team for the last MOSAiC leg, new crewmembers, provisions and fuel, as well as consumables.

- On 4 October 2019, following a fairly brief but intensive search, the participants in the MOSAiC expedition allowed their ship to freeze to the floe where they would subsequently erect their research camp for the drift through the Arctic Ocean. Finding the right floe proved to be an enormous challenge, since, after the warmest Arctic summer to date, there were very few floes in the expedition’s starting region that were suitably thick. The one they ultimately chose was formed – as they subsequently discovered – near the New Siberian Islands in December 2018, and had already covered a distance of 2,222 km, following a zigzagging course. Above all, the team valued one exceptionally stable area of the floe, which proved to offer a good location for the research camp. At the same time, other parts of the floe were relatively thin and dynamic, making them good representatives of the ‘new Arctic’; it was precisely this combination that made the floe an outstanding candidate for the planned scientific projects. In the course of the year, storms repeatedly produced new leads and pressure ridges, which at times made the expedition participants’ work much harder. But generally speaking, the floe remained stable to the very end – even during the melting season, when neighboring ice sheets broke up, one after the other.

- “Last autumn we looked for, found, scouted, colonized and investigated our floe from every possible perspective. Ever since, it has been a steadfast, stable basis for our research camp. Over the many months the ice floe has become our home, and we’ll always remember it fondly. But now it becomes water again. The time has come to bid it farewell and head north for the final phase of the expedition,” says Markus Rex.

• 06 July 2020: The New Siberian Islands were the birthplace of the MOSAiC floe: the sea ice in which the research vessel Polarstern is now drifting through the Arctic was formed off the coast of the archipelago, which separates the East Siberian Sea and the Laptev Sea to the north of Siberia, in December 2018. Sediments, and even small pebbles and bivalves, were incorporated into the ice during the freezing process, which the on-going melting process has brought to light on the surface of the MOSAiC floe. This is an increasingly rare phenomenon as nowadays most of the “dirty ice” melts before it even arrives in the Central Arctic. These are among the main findings of a study that MOSAiC experts have published now in the journal The Cryosphere, and which will provide the basis for numerous upcoming scientific assessments. 17)


Figure 22: Ice Rafted Debris (IRD) in Sea ice found on the MOSAiC Floe Fortress (Photo: Lisa Grosfeld)

- At first glance, it looks like a group of people with dirty shoes had left tracks all over the snow. But in reality, they are sediments, and even small pebbles and bivalves, which the on-going melting process has brought to light on the surface of the MOSAiC floe. When the sea ice formed, they were frozen inside; accordingly, they hail from the nursery of sea ice along the Siberian Shelf, which the experts have now used a combination of model simulations and satellite data to describe in detail. 18)

- The MOSAiC floe had already drifted over 1200 nautical miles in a meandering course when the research icebreaker Polarstern moored to it on 4 October 2019, at the coordinates 85° North and 137° East, and began to drift with it through the Arctic Ocean. While the current expedition team is busy taking readings in the Arctic, their colleagues back at home are analyzing the data gathered. The precise analysis confirms the first impressions from the beginning of the expedition: “Our assessment shows that the entire region in which the two ships looked for suitable floes was characterized by unusually thin ice,” reports Dr Thomas Krumpen, a sea-ice physicist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). Last autumn, the first author of The Cryosphere study coordinated research activities on the Russian icebreaker Akademik Fedorov, which accompanied the flagship of the MOSAiC expedition, the Polarstern, for the first few weeks. The Akademik Fedorov was also instrumental in deploying monitoring stations at various locations across the MOSAiC floe – collectively referred to as the ‘Distributed Network’.

- “Our study shows that the floe we ultimately chose was formed in the shallow waters of the Russian shelf seas in December 2018,” Krumpen explains. Off the coast of Siberia, strong offshore winds drive the young ice out to sea after it forms. In the shallow water, sediments are churned up from the seafloor and become trapped in the ice. Ice formation can also produce pressure ridges, the undersides of which sometimes scrape along the seafloor. As a result, stones can also become embedded in the sea ice. Now that the summertime melting has begun, all of this material is being revealed at the ice’s surface: “At several points we’ve found entire mounds of pebbles measuring several centimeters in diameter, plus a number of bivalves,” reports MOSAiC expedition leader Prof Markus Rex directly from the Arctic.


Figure 23: IRD (Ice Rafted Debris) in Sea ice found on the MOSAiC Floe Fortress during Leg 4. Brownish patterns on ice show the abundance of the gravels (Photo: Lisa Grosfeld)

- Meanwhile, back home in Bremerhaven, Germany, Thomas Krumpen is thrilled to see that the now emerging ‘bivalve ice with pebbles’, as he has affectionately dubbed it, so clearly confirms the study’s findings. The team of authors led by the AWI expert used a combination of satellite imagery, reanalysis data and a newly developed coupled thermodynamics backtracking model to reconstruct the floe’s origins. Now Krumpen and his colleagues are devising a strategy for gathering samples of the sediments. The extent to which these ‘dirty’ and therefore darker patches accelerate melting on the floe is an important question, and answering it could enhance our understanding of the interactions between the ocean, ice and atmosphere, of biogeochemical cycles, and of life in the Arctic in general.

- In addition to mineral components, the sea ice also transports a range of other biogeochemical substances and gases from the coast to the central Arctic Ocean. They are an important aspect of MOSAiC research on biogeochemical cycles, i.e., on the formation or release of methane and other climate-relevant trace gases throughout the year. However, as a result of the substantial loss of sea ice observed in the Arctic over the past several years, precisely this ice, which comes from the shallow shelves and contains sediments and gases, is now melting more intensively in the summer, causing this material transport flow to break down. In the 1990s, the Polarstern was often in the same waters where the MOSAiC expedition began its drift. Back then the ice was still ca. 1.6 meters thick at the beginning of winter, whereas it had shrunk to ca. 50 cm last year – which made the search for a sufficiently thick floe in the autumn of 2019 all the more difficult.


Figure 24: Aerial view of the MOSAiC ice floe during Leg 4, 30 June 2020 (Photo: Markus Rex)

- “We were fortunate enough to find a floe that had survived the summer and formed in the Russian shelf seas. This allows us to investigate transport processes from the ‘old Arctic’, which now only partly function, if at all,” says Krumpen. Particularly in the higher latitudes, global warming is causing temperatures to climb rapidly: in the summer of 2019, the last summer before the expedition, Russian meteorological stations reported record temperatures. These high temperatures sparked rapid melting and significantly warmed Russia’s marginal seas. As a result, many parts of the Northeast Passage were ice-free for a 93-day period (the longest duration since the beginning of satellite observation). The experts predict that if CO2 emissions remain unchecked – as they have in the past several years –the Central Arctic could be ice-free in summer by 2030.

• 26 June 2020: Overview of the MOSAiC Expedition, its current position as well as the entire course of the Expedition so far. 19)


Figure 25: Sea ice concentration 26 June 2020 (map credit: AWI, University of Bremen)

• 18 June 2020: After a month’s absence, on 17 June the German research icebreaker Polarstern rendezvoused with the MOSAiC floe at 82.2º North and 8.4º East, after having left it on 19 May 2020 to exchange personnel and bunker supplies near Svalbard. Full of energy, the research team for the fourth leg of the expedition, which consists of experts from 19 countries, is looking forward to continuing the one-year-long MOSAiC expedition and its research on the ocean, ice and atmosphere in the Arctic. Earlier this week, their predecessors from Leg 3 returned to Bremerhaven on board the research vessels Sonne and Maria S. Merian. 20)

- The location of Polarstern’s destination was never in doubt: autonomous monitoring stations transmit positioning data from the drifting floe at regular intervals. Far more importantly for research purposes, however, is the fact that the stations continued to gather a wealth of important data during Polarstern’s absence, e.g. on energy balances – energy transfers between the atmosphere, ice and ocean – and much more, ensuring that valuable time series on fundamental parameters could continue while the researchers were away. Needless to say, this is no substitute for on-site fieldwork; accordingly, the team for the Leg 4 is eager to get started.

- First impressions of the floe upon returning: “The thickest area of the floe, which we dubbed the fortress, has for the most part weathered the deformations in the spring quite well, and continues to offer a good basis for our research camp,” reports Prof Markus Rex, leader of the MOSAiC expedition, an atmospheric physicist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), and a professor at the University of Potsdam. “We’ll be able to continue working here well into the summer. But, with the extensive summertime melting that has now already begun, we’ll need to keep our instruments and installations highly mobile, and be ready to adapt to changing circumstances. Later in the summer, it may be necessary to relocate the camp – it all depends on how the ice conditions develop,” says Rex, who also led the first leg of the expedition, which began in September 2019. The lessons learned during the search for the ideal MOSAiC floe have now done him yeoman’s service: just like last autumn, the Polarstern dropped anchor just outside the research area, and sent teams out to scout the ice conditions. The ship will only maneuver into her final position a few days from now.

- Docking maneuvers are one of the many situations in which the captain’s experience and navigational skills are essential. After the latest crew exchange Thomas Wunderlich took over, relieving Stefan Schwarze. The two captains had – unlike all the other crewmembers – decided there would be only one exchange in the entire expedition. “What’s most important, just as it was back in the days of the early explorers, is to not just charge in, but to find the ideal position for entering the ice,” says Captain Wunderlich with regard to approaching the floe. “For the first few days, we made good and rapid progress, thanks to the prevailing winds and good visibility.” But from 82º North, the situation grew ‘tenser’: the ice dynamic increased, and the ice grew thicker. “As a result, on the weekend of 13/14 June, the pack ice slowed us to a standstill, forcing us to shut down the engines to conserve fuel. But coming to a dead stop like this also has the advantage of showing you: nothing about this venture is predictable or can be taken for granted – sometimes you just have to accept your circumstances,” Polarstern’s captain explains. His greatest wish: “... that we can stay with the floe as long as possible, so as to accompany it from birth through the end of its lifecycle – even though doing so will pose an enormous challenge for logistics and navigation.”


Figure 26: Autonomous Flux Station on broken MOSAiC floe. Photo taken from Helicopter two days before Polarstern arrived back at the floe after the exchange and supply off Svalbard (Photo: AWI, Markus Rex)

- “In the summer that’s just now beginning, we’ll investigate the processes at work in the Arctic climate during the melting season in unprecedented detail,” stresses Markus Rex. These include ocean eddies, which are produced below the ice by ocean currents; how the thickness and properties of sea ice influence climate processes; the role of snow cover on sea ice; and the nature of the interplay between the sea ice, atmosphere and clouds. The summertime melting has now begun, producing pools on the surface of the sea ice that alter its energy budget. When the ice ultimately breaks, the resultant leads and channels release water vapor and aerosols, which lead to cloud formation in the atmosphere. What the characteristics of these clouds are, and whether the cool or warm the lower atmospheric layers, are some of the other questions that the research team will explore before the Polarstern departs for her homeport in Bremerhaven, where the icebreaker is expected to arrive on 12 October, 2020.


Figure 27: Julia Regnery and Amy Macfarlane looking to MOSAiC Floe before they start their exploring tour on the MOSAiC Fortress. This was at the first day during Leg 4 when we reached the floe (Photo: AWI, Lisa Grosfeld)

- On 15 June 2020, the team from Leg 3 arrived in Bremerhaven on the research vessels Maria S. Merian and Sonne. They had departed for the expedition from the Norwegian port of Tromsø in late January, and had continued their fieldwork substantially longer than originally planned. Hopefully they enjoyed their return trip just as much as Thomas Wunderlich and his crew, who found themselves in the unaccustomed role of ‘passengers’ on board other research ships: “I’d like to take this opportunity to thank the crews of the Maria S. Merian and Sonne for their openness, friendliness and hospitality. It was a real pleasure, and we learned a thing or two. But I’m confident the feeling is mutual,” says Thomas Wunderlich of the journey to the Arctic.


Figure 28: The next MOSAiC milestone is reached. We just finished another 5 days to handover all our knowledge and experiences about our MOSAiC floe of the last couple of months to the team of Leg 4 (Photo: AWI, Christian R. Rohleder)

• 05 June 2020: For the first time on the MOSAiC expedition, the Polarstern Captain will be exchanged. After 260 days out at sea, Thomas Wunderlich will take over for Captain Stefan Schwarze for the remaining expedition. ”Originally, the Captain exchange was planned in April via an airplane. ”It's now a different challenge to take over the ship after Polarstern came out of the ice. We [the new team] have the advantage of being impartial [in continuing the work], but on the other hand, we have to newly establish the infrastructures on the floe. We have to be prepared to master challenges around dynamic ice such as thinner ice and the build-up of leads [...]. The challenge is now to continue with what is left behind,” said Polarstern Captain Thomas Wunderlich. 21)


Figure 29: Exchange of the Polarstern Captain at Svalbard for the continuation of the MOSAiC Expedition (image credit: AWI)

• 04 June 2020: It's done! 20 days ago, we left our MOSAiC floe. On the following transit to the ice edge, the ice did not really act in our favor. But on Tuesday (02 June), 23:10 ship's time, we finally passed the ice edge. An emotional moment that came in the end much faster than expected as the ice edge was rather sharp. Circumstances which were already implied by the satellite images of the area. Thus, already, a few minutes after passing the ice edge, we saw nothing else than a blue ocean in front of us. While the ice-covered ocean was a faithful companion for 119 days, we saw the mountains of Svalbard on the port side since yesterday morning. During the night, we met the supply vessels Maria S. Merian and Sonne in front of the entry of the fjord, in which we now started the bunkering operations as well as the handover procedures between the ships. Now, a couple of exciting days are ahead of us in which we , from leg 3, will recall our memories and experiences from the time in the ice to pass them over to the different teams of Leg 4. 22)

• 26 May 2020: Scientists and researchers from around the world spent five years planning the $155 million MOSAiC expedition during which the Polarstern research vessel would drift enclosed by sea ice across the Arctic Ocean for 13 months. Expedition leaders of the MOSAiC project, spearheaded by Germany’s AWI (Alfred Wegener Institute), planned for countless eventualities and challenges the Arctic Ocean may throw at them. Except for a global pandemic which presented seemingly-insurmountable logistical challenges. 23)

- How would the expedition ensure the timely resupply and exchange of crew and staff with borders closing and international travel grinding to a halt? Norway’s Svalbard archipelago, which was intended as a staging hub for flights ferrying scientists to and from the Polarstern, closed for international visitors.

- Expedition leaders had set a deadline of April 20 to come up with alternatives to resupply the Polarstern and conduct crew and staff exchanges. A number of backup options, including chartering icebreakers, resulted in dead ends. Even Russian and Chinese counterparts offered assistance, but their research icebreakers were already located in, or en route to, Antarctica.

- “Behind the scenes people (are) working really hard to come up with solutions, and the solutions just keep slipping away,” Matthew Shupe, climate scientists and co-coordinator of MOSAiC said at the time.

Bringing Polarstern out of the ice

- A solution came in the form of two German vessels — RV Sonne and RV Maria S. Merian. Usually the use of these research vessels has a two-year lead time, but during these extraordinary circumstances assistance came quickly and unbureaucratically.

- The two ships departed Bremerhaven, Germany last week and arrived near Svalbard this past weekend, ready to rendezvous with the Polarstern to conduct the resupply and exchange of crew. Originally the Polarstern was supposed to remain in the pack ice for a whole year, but the COVID-19 pandemic necessitated a change of plans.

- “We’re going to unfortunately have to bring the ship out, and this is not part of the original plan. But it’s the way logistics play out right now,” explained Shupe in a recent radio interview.

- Throughout the last month the Polarstern experienced a rapid southward drift resulting in a southerly location in April that it was not expected to reach until August. This drift path brought it relatively close to Svalbard making a resupply mission near archipelago feasible.

Slow progress in thick ice

- While RV Sonne and RV Maria S. Merian sailed from Germany to Svalbard in around a week, the Polarstern’s journey out of the ice has been more challenging due to thick ice conditions. The researchers packed up much of the science camp, except for some instruments left behind to continue recording data autonomously, and the ship departed from the ice floe on Saturday, May 16.

- It was expected to reach the waters of Svalbard the morning following Saturday, May 23. However, thick second-year ice represented a formidable challenge for the research icebreaker. At times the ship had to use back-and-forth ramming technique to push through the ice.

- “Indeed Polarstern’s progress is quite slow at the moment — but nothing completely unexpected, as ice and weather conditions in the Arctic can always slow down the ship’s speed,” explained Folke Mehrtens of the Alfred Wegener Institute to HNN (High North News).

- When ice conditions become too severe the ship’s experienced crew decided to turn off the engines and instead drift with the ice floe until they encountered less dense ice. This approach also reduced fuel consumption.

- “There is no extremely high fuel consumption as the experienced crew shuts down the engines when the ice conditions become too demanding,” elaborated Mehrtens.

- High fuel consumption had become an issue earlier this year when the Russian icebreaker Kapitan Dranitsyn traveled into the pack ice to resupply and exchange crew. Due to severe storms and numerous detours to get around impassable ice the vessel ran low on fuel when it finally reached the Polarstern on February 28. A third ship had to be dispatched to refuel the Kapitan Dranitsyn.

Thinner ice allows for progress

- After traveling just 70 nautical miles during the first week and with more than 130 nautical miles to go until the ice edge to the North of Svalbard, the ship finally found a lead in the ice allowing them to make steady progress. The vessel managed to travel more than 20 nautical miles in around eight hours Monday. The vessel is now expected off Svalbard by the weekend, the Alfred Wegener Institute confirmed to HNN.

- After the resupply and crew exchange the vessel will be racing back to the ice camp in the hope of returning in time to observe the beginning of the annual seasonal melt.

- With the southerly location of the ice camp it is unlikely that the ice floe will survive the summer melt season making it likely that the expedition will relocate further north during the next eight weeks to remain enclosed by ice throughout the summer.

• 06 May 2020: Hi there, from 39,000’. I’m Melinda Webster, a sea ice geophysicist at the University of Alaska Fairbanks’ Geophysical Institute. I’m on my way to the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) Expedition as the Ice Team Lead for Leg 4. Funded under NASA’s New Investigator Program, I’ll be using MOSAiC data as the ultimate blue print to evaluate and extend the seasonal capability of ICESat-2 data for sea-ice research. 24)

- About 1.5 months ago, I was packed, medically cleared, and ready to fly to the R/V Polarstern from Alaska via Svalbard for the MOSAiC expedition. About 1.4 months ago, COVID-19 was declared a pandemic. Plans set so carefully into place vaporized within a matter of days.

- After a false start, packing for a 4+ month expedition gets much easier. You have time to tie up loose ends, have more opportunities to talk with loved ones, and reluctantly finish off projects that were being procrastinated. And, in this case, enjoy the return of spring before heading into a world where the vibrant colors of budding trees and flowering plants are nowhere near. Instead, the Arctic sea-ice cover is a stunning realm with every blue and grey tone imaginable, and is certainly no less beautiful than springtime on land.


Figure 30: My travel itinerary: I got as far as Seattle in March. On April 29, I picked up my travel again and headed east to Bremerhaven. From Bremerhaven, we’ll travel to Svalbard via ships to meet the R/V Polarstern. It’s too bad there aren’t direct flights between Fairbanks and the Polarstern (image credit: Melinda Webster)

- The COVID-19 disruptions have also given the MOSAiC Project Board and funding agencies time to compose a logistical masterpiece centered on safely continuing the MOSAiC expedition during a pandemic. Part of this masterpiece ensures that MOSAiC participants travel as safely as possible to the ship to successfully rotate the crew and scientists. Through the NSF (National Science Foundation), each U.S. MOSAiC participant for Leg 4 received a care package of personal protective equipment: masks, gloves, hand sanitizer, disinfectant wipes, disposable thermometers, and more. So far, my flights have been at least 50% empty, leaving ample breathing room, and 99% of people have donned masks.


Figure 31: JFK (John F. Kennedy) airport in New York. There’s hardly anybody here and 98% of the shops and restaurants were closed (image credit: Melinda Webster)

- Upon our arrival in Hamburg, we’re to be transported to a hotel in Bremerhaven to start a 2-week quarantine and a series of COVID-19 tests. Once clearing quarantine, tests, and safety training, we’ll take two research vessels from Bremerhaven to Isfjord, the main fjord in Svalbard that leads to Longyearbyen. Although Norway is closed to visitors, we’ll meet the Polarstern in this fjord to carry out the rotation without needing to step foot on land. I anticipate the experience will be overwhelmingly joyful. Our colleagues who set out for a 2-month expedition in February were instead given a 5-month tour due to the pandemic. I’m looking forward to relieving them of their work and continuing the time-series that will make MOSAiC an invaluable expedition and improve our use of ICESat-2 data.


Figure 32: NSF sent us a wide variety of masks (N95, cloth, etc.), photo credit: Melinda Webster

• 05 May 2020: The Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) together with the German Federal Ministry of Education and Research (BMBF) is stepping in to support the MOSAiC expedition in the Arctic Ocean by sending the research vessels Sonne and Maria S. Merian to Spitsbergen (Svalbard). There they will rendezvous with the research icebreaker Polarstern and perform a complete changeover of approximately 100 personnel as well as exchanging cargo and supplies. "We are delighted to be able to support the MOSAiC expedition in this way," said DFG President Professor Dr. Katja Becker in Bonn. "We are preventing the premature termination of the project and therefore protecting research from the loss of extremely valuable data." 25)

- As the originally planned supply trips by Russian, Swedish or Chinese icebreakers cannot currently take place due to the coronavirus pandemic, and it is also impossible to change crews and science teams by aircraft via Spitsbergen or Greenland, an alternative plan was required. Within a matter of days, the responsible decision-making bodies at the DFG agreed to a plan worked out by the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI) and the German Research Fleet Coordination Center at Universität Hamburg.

- The two vessels, Sonne and Maria S. Merian, will depart from Bremerhaven on 18 May 2020 with around 100 passengers and various equipment and accommodation containers. A few days later, in a sheltered ice-free fjord in Spitsbergen, the ships will then rendezvous with the Polarstern, which is interrupting its measuring program for approximately three weeks to meet the other vessels. After the passengers and equipment have been transferred, the research icebreaker will return to its original position. Strict quarantine and testing measures will be observed for at least 14 days before the vessels depart to avoid, as far as possible, spreading SARS-CoV-2 to the Polarstern.

- The Maria S. Merian is jointly funded by the DFG and the BMBF as a central research facility. The DFG bears 70 percent of the operating costs for the vessel and the BMBF covers the remaining 30 percent. Due to the travel restrictions imposed in response to coronavirus, the Maria S. Merian cannot currently be used for any other scientific purposes and, like the BMBF-funded Sonne, was forced to halt its cruise program at the end of March 2020.

- The Polarstern, which is operated by the AWI, has been in the Arctic Ocean since September 2019 as part of the international project MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate). With a total budget of over €140 million, a duration of 390 days and a team of approximately 600 scientists from 20 nations, MOSAiC is the most ambitious polar expedition ever launched. For the first time, MOSAiC is enabling researchers to study the Arctic climate over a whole year, including the Arctic winter, with a wide range of measuring instruments. The Polarstern serves as the central research station and base camp. Securely anchored to a large ice floe, it is drifting southwards with the movement of the sea ice. Its current position is approximately midway between the North Pole and Spitsbergen.

• 28 April 2020: With aerial and icebreaker resupply missions scrapped, the Polarstern icebreaker will leave the ice camp and rendezvous with two German research vessels to transfer staff and provisions. 26)

- Project leaders of the year-long MOSAiC science expedition presented an innovative solution to overcoming the logistical challenges arising from ongoing travel bans in light of the Corona pandemic. Rather than having supply ships come to it, the Polarstern will exit from the ice and meet two research vessels off the coast of Svalbard to exchange 100 staff and restock provisions.

- The ship has been drifting across the Arctic Ocean enclosed by sea ice since last Fall. Originally the project organizers had planned to conduct five crew exchanges and resupply missions over the course of the 13 month project.

- While the first two crew exchanges at the end of 2019 and in late February happened as planned, an aerial transfer of staff and resupply out of Svalbard had to be canceled as Norwegian authorities have placed the archipelago on lockdown due to the pandemic.

No icebreakers available

- In early April project leaders had considered chartering an icebreaker or moving a planned resupply mission of the icebreaker Odin from mid-June to mid-May. However, none of these options turned out to be feasible in light of the travel restrictions.

- “The current situation also means [that] the international icebreakers that were originally meant to resupply the expedition are also prohibited from making any staff transfers,” explain officials from the Alfred-Wegener-Institute (AWI), the lead German government-funded research organization behind the expedition. “The massive restrictions on global travel hindered the third team exchange, which had been planned as an aerial transfer in early April, using the Spitsbergen archipelago as a base of operations.”

- The organizers now intend to bring the Polarstern out of the ice and rendezvous with two German research vessels, RV Sonne and RV Maria S. Merian, in calm waters off Svalbard to conduct a full swap of around 100 staff and researchers and provide a full resupply. Afterwards the Polarstern will return to the ice and continue its scientific work. Both RV Sonne and RV Maria S. Merian are currently docked in the north German port of Emden after having returned from South Africa and Uruguay, respectively.

Close to Svalbard already

- Fortunately the drift corridor of the Polarstern has already taken the vessel in the direction of Svalbard and it is currently located between the North Pole and Fram Strait. “For the upcoming logistical operation, this position is advantageous. Some instruments on the MOSAiC ice floe will continue recording autonomously until Polarstern returns, while others will be dismantled,” explains the AWI.

- The project leaders may also use the Polarstern’s departure from the ice as an opportunity to relocate the ice camp closer to the North Pole. This possibility has always been part of the planning scenarios in case the ship drifted faster than anticipated and will not have an impact on the scientific research being conducted. “If we drift too far south, we will set up the Ice Camp again farther north, and continue our observations in a region where the Central Arctic is still covered with ice in the summer. We’re thrilled with the tremendous amount of data we’ve been able to gather over the past seven months,” states expedition leader Prof Markus Rex from the AWI.

- “With this alternative plan, the AWI’s Logistics Team, together with our international partners, achieved a true masterstroke in the face of the enormous challenges posed by the coronavirus crisis,” continues Rex. “The pandemic forced us to devise a complex alternative scenario for wholly new, unforeseen and unprecedented circumstances.”

- With this unconventional solution the continuation of the expedition has been secured according to the AWI.


Figure 33: Location of the Polarstern on April 27, to the North of Svalbard (graphic: Courtesy of AWI)

Quarantine and testing for all staff

- In order to ensure the safety of all participants and keep COVID-19 off the Polarstern the relief crew and researchers heading to the Arctic will be undergoing a monitored quarantine phase starting in early May.

- This change of plans also means that there will only be four crew exchange and resupply missions as compared to the five originally planned. No details have yet been given on when and how the fourth and final transfer will be conducted. Originally, the last two exchanges were supposed to happen in mid-June and mid-August using the Swedish icebreaker Oden and the Chinese icebreaker Xue Long. The mission, which costs an estimated 130 million euros, is expected to end as planned in mid-October.

• 24 April 2020: Despite the current challenges, the MOSAiC expedition will continue. After many national borders were closed in response to the coronavirus pandemic, one team transfer had to be postponed. But thanks to new alternative plans supported by the German Federal Ministry of Education and Research, the German Research Foundation and the operators of the German research fleet as well as the dedicated work of the expedition team currently on board, MOSAiC will soon enter its next phase. An interim review of the project shows: the data to be gathered over the next several months will be indispensable for the scientific community. 27)

- After successfully completing the first half of its more-than-a-year-long drift through the Arctic Ocean, the international expedition MOSAiC suddenly faced unforeseen challenges, posed by the coronavirus pandemic. The massive restrictions on global travel hindered the third team exchange, which had been planned as an aerial transfer in early April, using the Spitsbergen archipelago (which Norwegian authorities have since placed off limits due to the pandemic) as a base of operations. Since the current situation also means the international icebreakers that were originally meant to resupply the expedition are also prohibited from making any staff transfers, in the span of just a few weeks the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), the MOSAiC Coordination Office and the funding bodies and operators of the German Research Fleet Coordination Centre at Hamburg University developed a completely new alternative plan:

- The upcoming transfer will be implemented with the aid of the German research vessels RV Sonne and RV Maria S. Merian. As a result of the pandemic-related measures, both ships have just returned to Germany. Polarstern will meet the two vessels in calm waters off Svalbard, in order to carry out a complete personnel transfer (ca. 100 people), and an exchange of cargo and provisions. Once the process is complete, Polarstern and her new team will return to the ice and continue their expedition in the Arctic Ocean.

- Expedition Leader Prof Markus Rex from the AWI: “With this alternative plan, the AWI’s Logistics Team, together with our international partners, achieved a true masterstroke in the face of the enormous challenges posed by the coronavirus crisis. With a host of alternative plans at the ready, the expedition was prepared for virtually every scenario imaginable. Yet the pandemic forced us to devise a complex alternative scenario for wholly new, unforeseen and unprecedented circumstances. We thank the operators of the German research fleet, the German Research Foundation and the Federal Ministry of Education and Research. Moreover it was only the team’s tremendous commitment and flexibility that allowed us to conduct climate research in the Arctic ice two months longer than planned, despite the current conditions. As a result, in spite of the extremely adverse conditions, the continuation of the expedition has been secured.”


Figure 34: RV MERIAN in the Ice (Photo: Universität Hamburg/LDF/K. v. Bröckel)

- The new staff exchange plan will be accompanied by extensive safety concepts developed in close collaboration with the respective health authorities. From early May, the participants in the next leg of the expedition living in Germany will enter a monitored quarantine phase, during which they will be regularly tested for the coronavirus. Due to the delayed exchange, there will only be a total of four, not five, transfers in the course of the expedition, but this will have no effect on its total duration: the planned end date is still 12 October 2020.

- Prof Torsten Kanzow from the AWI, the current chief scientist on board Polarstern, had the following to report: “Many of our people have families, and are of course doing everything they can to stay in close contact with their loved ones back home via satellite phone and email. As the expedition leader, I also note the hardships and concerns of the people on board, and pass them on to the Coordination Office and the AWI. This has helped us regain a bit of certainty in our planning efforts.” In addition, on 22 April seven participants, whose personal circumstances made it impossible to stay longer, were flown out with a Twin Otter. According to Kanzow, he’s happy to see that, despite the current challenges and concerns, the participants have continued to carry out their research duties in the ice with great enthusiasm – even though, since 31 March, they have had to do so in the never-ending sunlight of the Polar Day.


Figure 35: On 22 April 2020 seven MOSAiC participants were flown out with a Twin Otter. Their personal circumstances made it impossible for them to stay for the longer duration of leg 3 (Photo: Christian R. Rohleder)

- Over the past months, Polarstern has rapidly advanced along her projected drift corridor; as a result, she is already between the North Pole and Fram Strait, i.e., fairly far to the south. For the upcoming logistical operation, this position is advantageous. Some instruments on the MOSAiC floe will continue recording autonomously until Polarstern returns, while others will be dismantled.

- Depending on how the drift progresses, the Ice Camp may be relocated closer to the North Pole. The possibility of tearing down and relocating the camp was always part of the planning scenarios, in the event that the ship drifted faster than anticipated. This would have only minimal effects on the expedition timeline. As Markus Rex explains, “If we drift too far south, we will set up the Ice Camp again farther north, and continue our observations in a region where the Central Arctic is still covered with ice in the summer. We’re thrilled with the tremendous amount of data we’ve been able to gather over the past seven months. Despite the current adversities, we hope to continue the expedition for the remainder of the year-long cycle, and draw it to a close in October as planned.”

• 17 March 2020: Caught in the glare of Polarstern’s spotlights, a curious mother polar bear and her cub explore the MOSAiC ice camp – with this image Esther Horvath, a photographer and photo editor at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), won the World Press Photo Award for an individual picture in the category “Environment”, as the World Press Photo Foundation announced on the evening of 16 April. 28)


Figure 36: Polar bear mom and cub visit the ice floe (Photo: Esther Horvath)

- “For me as a photographer, winning a World Press Award is almost like taking home the Oscar in the film industry,” says Esther Horvath. “It’s always been one of my greatest dreams, and I’m delighted that I won it for my photographic coverage of the MOSAiC expedition.”

- The World Press Photo Award is the world’s premier competition for press photography. Every year, the jury of experts recognizes professional photographers for their outstanding individual photographs. To be eligible, the respective photo has to have been taken within the past twelve months. Esther Horvath’s award-winning shot documents one of the first polar bear sightings during the MOSAiC expedition, one of the sensational moments in its first few weeks. The photo was released on 22 November 2019 in an article on MOSAiC published in the New York Times. For the award, photographs can be submitted in one of eight categories: Contemporary Issues, Environment, General News, Long-Term Projects, Nature, Portraits, Sports, and Spot News. Normally the awards are presented at a festive ceremony in Amsterdam; this year, due to the corona virus crisis, there will be a videoconference instead. Afterwards, the winning photos will go on a one-year-long tour, covering 120 cities in 50 countries.

• 20 March 2020: In the last post, we took a brief tour of some of the sites that make up MOSAiC. In the days since, much has changed with the MOSAiC floe. Specifically, leads have formed in the ice pack that have altered our floe map and impacted our daily schedules drastically. 29)

- Put simply, a lead is just a crack in the ice. It’s never that simple, however. There are many complex processes that determine where and when leads form, how wide they can become, and whether or not they close back up or just re-freeze. Although leads are common features in sea ice and are vitally useful for satellite measurements of sea ice thickness, they still serve as a not-so-gentle reminder that the sea ice can be extremely dynamic, and that we have to be prepared for anything when working out on the ice.

- A few days ago, a small crack formed near the ship that was just a few inches wide when it was first noticed. We were still able to go out on the ice, but it was being monitored closely. About an hour later, everyone out on the ice got a radio call from the ship that it was time to return. The crack had grown to a few meters wide, and ran directly under the ship and out in both directions. It continued to widen for a few hours, but luckily this first crack didn’t form under any installations or sensitive instruments. This lead, however, was just the start.

- In the next hours and next days, many other leads formed off of that initial crack. Some stayed only 1 meter wide, while others grew to 10 meters or more. Almost all work on the ice has been limited, and the leads are monitored closely. The most critical lead formed between the Central Observatory and two important sites: Met City and the Remote Sensing Site. It shifted the sites a few dozen meters from their previous location, to the point where the power cables had to be disconnected before they snapped.


Figure 37: A lead running beneath Polarstern and through the MOSAiC floe, captured from a drone (image credit: Manuel Ernst/UFA)

- While the leads themselves pose threats to the instruments and infrastructure on the ice, they are only half of the concern. When (and if) the leads close again, there is a possibility that ridges could form when the two sheets of ice collide together again. Ridges can grow to several meters tall and would crush anything that was caught in the middle. For now, we are keeping an eye on everything that is on the ice in order to limit any impact that the leads or ridges may have. We also keep our fingers crossed that the ice stabilizes soon!


Figure 38: A large (about 3 m tall) ridge that formed in the vicinity of Polarstern. The unconsolidated nature of the ice blocks shows that this ridge formed relatively recently (image credit: Steven Fons)

• 16 March 2020: On Thursday 12 March, the Norwegian government announced comprehensive measures to combat the spread of the corona virus, effective immediately. As a result, all travellers to Norway from non-Nordic countries who do not have a residence permit will most likely have to immediately leave the country again or be placed in quarantine for 14 days. In response, and due to the highly dynamic development of the corona pandemic, on Friday 13 March the MOSAiC project management decided to temporarily suspend the aerial survey campaigns planned for this spring and based in the Svalbard archipelago, which is under Norwegian administration. There are currently three icebreakers underway in the Central Arctic for the MOSAiC expedition. 30)

- The survey flights, focusing on the atmosphere and sea ice, were to be carried out in four sub-campaigns from March to September. The two research planes Polar 5 and Polar 6 were originally scheduled to reach Svalbard on 11 March. After a participating researcher tested positive for corona last week, the start of the campaign had to be pushed back. In light of the current situation, the sub-campaigns planned for spring will no longer be possible.

- “The highly unusual situation at the moment leaves us no choice. We’d like to thank everyone who was involved in the months of preparation, and who did everything within their power, up to the last minute, to make the flight campaigns a reality,” says Dr Andreas Herber from the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI), and coordinator of the MOSAiC airborne campaigns. According to Herber, the AWI will closely monitor the situation over the next several weeks and explore alternative solutions, e.g. extending the two sub-campaigns scheduled for the summer.

- In the meantime, on board the icebreaker Polarstern, the MOSAiC expedition continues. The ship’s current coordinates are 87°7’ North and 16°59’ East. Those researchers and crew returning from the second leg of the expedition on board the Russian icebreaker Kapitan Dranitsyn have made good progress through the ice since departing from the MOSAiC floe on 6 March. On 14 March they rendezvoused as planned with another Russian icebreaker, Admiral Makarov, at 84°48’ North and 42°35’ East, to bunker additional fuel for the voyage home.

- Moreover, the planned crew exchange by airplane in early April should – barring unforeseen developments – still be possible. Nevertheless, both the project management and participants are preparing for the additional challenges the pandemic may entail. For example, Norway’s quarantine policy will most likely remain in effect in April, which means participating researchers will need to allow a great deal of time prior to the fourth leg of the expedition. All participants have been requested to use the utmost caution to avoid infection. Before being allowed on board the ship, they will be tested for corona twice: once before leaving their point of origin, to avoid spreading the virus by travel, and once more at the expedition’s point of departure, to minimize the risk of introducing the virus among the expedition team. Further, Polarstern is equipped with a quarantine ward, in the event that, despite all precautions, there is an infection on board.


Figure 39: The MOSAiC aerial survey campaigns with Polar5 and Polar6 are temporarily suspended (photo credit: Alfred-Wegener-Institute)

- “We’ve rapidly responded to the pandemic with a comprehensive safety concept and strict medical-diagnostic profile, in order to reduce the risks for all expedition participants to a minimum. The spreading wave of infections poses an immense challenge for this international expedition. Our safety concept represents a commensurate response to the current situation. That being said, no one can predict how that situation will change over the next few months; therefore, we will continually reassess and update the concept as needed. For the time being, we have to ‘navigate by sight’ and focus on finding the safest and most sensible course for the logistical operations at hand,” says MOSAiC Expedition Leader Prof Markus Rex from the AWI. In this regard, the expedition closely collaborates with the health authorities of the countries involved, he adds, focusing on the health and safety of all expedition participants as the highest priority.


Figure 40: MOSAiC participants watch the arrival of the Admiral Makarov on the bridge of Kapitan Dranitsyn (photo credit: Benjamin Rabe)

• 16 March 2020: Central to the entire MOSAiC Expedition is the MOSAiC Floe: a large sheet of sea ice that was carefully selected back in October as the ideal place to anchor Polarstern for an entire year. It was chosen due to its size, structure (a mix of thick multiyear sea ice and thinner first year sea ice), and forecasted drift trajectory. Over the past five months, it has become a second home for many scientists. Here’s a brief tour of our workplace: 31)

The Central Observatory (CO):

- Nearest to Polarstern, the CO, is the primary place where measurements are taken, both from continuously operating instruments and from sampling trips off of Polarstern. It houses many installations, from small stakes just a few inches tall, to larger huts and tents that can comfortably fit a few people inside, to 25-meter-tall towers with dozens of instruments installed. Most installations are grouped into ‘cities’ by scientific discipline. There is MET (meteorology) City, Ocean City, Balloon Town (for weather balloons – not clowns), the Remote Sensing Site, and the ROV (Remote Operated Vehicle) Site, to name a few. There are also clean areas dedicated to the sampling of snow, measuring ice strength, and studying biogeochemical processes.

- Throughout the CO, there are carefully placed roads that lead from Polarstern through the Logistics area (where snowmobiles and other gear are parked) and to the different cities. Perhaps most importantly, there is also a ‘trip wire’ alarm around the CO that is able to send up a signal flare if a polar bear walks into it, providing an additional safety measure when out on the ice.


Figure 41: A map of the MOSAiC Floe, focused on the Central Observatory (image credit: AWI)

Area II:

- Outside of the CO is known as Area II. This mainly houses the “Dark Site” – a place where sea ice cores are taken each week. The Dark Site consists of two different locations from which cores are drilled: a first year ice site and a second year ice site. This area is located far from the lights of Polarstern and kept as dark as possible, so as not to disturb some of the ecological work that is going on. During the winter darkness, anyone visiting the Dark Site had to use a red headlamp, which has been proven to have the least impact on the organisms living below the ice. Due to the distance away from the CO and Polarstern, visiting Area II requires additional preparation and safety gear. My main task on MOSAiC is drilling sea ice cores, so I will venture to Area II at least once per week during leg 3.

The Distributed Network (DN):

- Furthest from Polarstern is the Distributed Network, which is home to exclusively autonomous instrumentation. The DN sites are not part of the MOSAiC Floe, but instead range from around 5 kilometers to over 30 kilometers away from Polarstern. Almost all sites require a helicopter to visit, usually these visits consist of fixing broken instruments or changing batteries. The purpose of the DN is to have measurements far from Polarstern, in order to determine the representativeness of the MOSAiC floe with respect to the ice in the rest of the Central Arctic.

- Together, these areas make up the field sites of MOSAiC. It’s a pretty cool place to work!

• 13 March 2020: The MOSAiC Leg 3 team is officially on board Polarstern, and science activities have quickly begun. 32)

- The first few days on board were filled with handover activities from the previous leg of the expedition. Leg 3 scientists met with members from leg 2 to get a general introduction to the instruments, experiments, and life on the MOSAiC ice floe. Given that leg 2 was on Polarstern since late December, they truly are experts in the scientific activities occurring out on the ice.

- During the handover, I met with members of the leg 2 ice team and visited different sites around the floe where most of my work will take place. Since it is my first time on Polarstern, I was also shown where different labs and workspaces are located, where to find tools and instruments to take out into the field, and, perhaps most importantly, where the coffee machine is! These days were invaluable for preparing the leg 3 members for work, and even more important to ensure that MOSAiC continues to run smoothly with a new team at the helm.

- After the handover, it was time to say farewell to leg 2. We sent them off in true ‘Arctic expedition’ style with a gathering out on the sea ice between the two ships. All members from the science teams as well as the crews from both the Polarstern and the Kapitan Dranitsyn were invited for bonfires, hot tea, and group photos. The next morning, Kapitan Dranitsyn left on its return voyage to Tromsø, and leg 3 was left alone on Polarstern.

- It didn’t take long for us to get started. The morning of the Dranitsyn departure, some teams already set out onto the ice to take measurements. I was working with another member of the ice team to construct a radiation station that we deployed on the ice a few days later. This type of station holds a few instruments that detect the amount of solar radiation both above and below the sea ice. It was necessary to deploy these instruments early in the leg, so that they would be operational for the first sunrise of the year. So far, we have been in a state of constant twilight – a red-orange sky for most of the day. In a few days, the sun will rise above the horizon for the first time in 2020. With this new station (Figure 43), we will now be able to measure the amount of solar energy that reaches (and penetrates through) the sea ice.

- It has been extremely busy since leg 2 departed, but everyone is excited to be working on the ice. Here’s to a successful leg 3!


Figure 42: Scientists from MOSAiC Leg 3 walk from the Kapitan Dranitsyn to their new home on Polarstern (photo credit: NASA, Steven Fons)


Figure 43: Alexey (left) and Steven (right) deploying the radiation station (photo credit: Philipp Anhaus/AWI)

• 02 March 2020: For days, fast sea ice had slowed the progress of the resupply icebreaker Kapitan Dranitsyn; bound for the North Pole, her mission was to support the second exchange of researchers and crew in the MOSAiC expedition. Nevertheless, she steadily drew closer to her destination, and finally, at 12:20 pm (CET) on Friday, 28 February, dropped anchor 970 meters from Polarstern, moored to the same floe. While the handover is in full swing on the MOSAiC floe, in Russia another icebreaker will soon leave port in order to supply Kapitan Dranitsyn with additional fuel on her return trip. 33)

- This past week there were not one, but two new records in the history of polar research, as the University of Cambridge’s Scott Polar Research Institute has reported: on 24 February Polarstern’s drift took her to 88°36’ North, just 156 kilometers from the North Pole. Never before had a ship ventured so far north during the Arctic winter. And two days later, the Russian icebreaker Kapitan Dranitsyn, shortly before her rendezvous with Polarstern at 88°28’ North, reached the northernmost position on her mission, marking the first time a ship had made it so far north under her own power, so early in the year.

- “These records represent milestones in the MOSAiC expedition. They demonstrate the success of the logistical concept, and provide the basis for the unprecedented scientific data that is being gathered during the expedition,” says Prof Markus Rex from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Potsdam, Leader of the MOSAiC expedition. “My hat goes off to Captain Alexandr Erpulev for successfully navigating the icebreaker Kapitan Dranitsyn through the Arctic winter and virtually to the North Pole,” adds Polarstern Captain Stefan Schwarze, underscoring this nautical achievement. “Given the current sea-ice situation, the delay is absolutely in keeping with what had to be expected,” Rex emphasizes. Following the first few months of the expedition, Rex returned from the Arctic on board Kapitan Dranitsyn and will return to Polarstern in April.

- Together with the Logistics Division of the Alfred Wegener Institute, he’s spent the past several days working out how to provide the resupply icebreaker with additional fuel. Since the fast sea ice forced Kapitan Dranitsyn to consume more fuel than originally planned, the icebreaker Admiral Makarov is expected to depart from Murmansk on 3 March and follow an intercept course with Kapitan Dranitsyn, so as to refuel the latter in the Arctic sea ice.

- The exchange of staff and equipment is taking place on foot, with snowmobiles and with snowcats hauling heavily laden sledges. On board Polarstern and in the Ice Camp, the new expedition members are being instructed on various tasks by their predecessors. Extreme caution is the prime rule, especially when working on the ice, where the wind-chill temperature can now reach 58 degrees below zero Celsius. Thanks to these extreme temperatures, only a day after her arrival, the channel of open water left behind by Kapitan Dranitsyn had refrozen so rapidly and intensively that the researchers could walk on it. The temperatures also pose a problem when it comes to transferring provisions; for example, fresh produce has to be transported in heated containers. It’s still too soon to say how long the transfer of crew and equipment will take to complete, partly because the two ships’ cranes only work very slowly in the frigid conditions.


Figure 44: The icebreakers Kapitan Dranitysn and Polarstern in the Arctic ice (photo: AWI, Ernst Stürmer)

- Shortly before beginning the journey home, Prof Christian Haas from the Alfred Wegener Institute, Chief Scientist for the second leg, took stock of the situation. According to the sea-ice expert, “Over the past few months, we’ve been able to observe winter at the North Pole more consistently and precisely than ever before. The ice thickness has doubled to an average of 160 cm since December, which corresponds to a growth rate of roughly ten centimeters per week.”

- In addition, with the aid of helicopter laser-scanner readings, Polarstern’s radar system, and buoys, the researchers were able to observe how the ice deformed, and channels opened and closed again. Thanks to the warming of the Arctic Ocean, smaller and thinner ice floes are becoming more common. Driven by the wind, they can collide and overlap, producing pack ice hummocks up to four meters tall. Since a great deal of their mass lies underwater, some hummocks are 20 to 30 meters thick – a phenomenon that now represents a challenge for the resupply icebreakers.

- In contrast, readings taken on the ice, on board ship, and with weather balloons revealed that the air temperature just above the ice was far lower than at a height of 20 meters. In the lowermost ten meters there can be temperature differences of more than 4 degrees Celsius, which has a major influence e.g. on the increase in ice thickness. Lastly, ROV dives showed how life under the ice goes on, even in the long Polar Night. “We’ve never had the opportunity to study the zooplankton and polar cod up here so extensively at this time of year. In February we even repeatedly saw a seal under the ice, which is apparently finding sufficient food, despite being practically at the North Pole. And on the surface, we sighted a polar bear and several Arctic foxes,” says Christian Haas, summarizing recent observations.

- Sometime in the next few days Prof Torsten Kanzow from the Alfred Wegener Institute, who arrived on Polarstern by helicopter last Wednesday, will take over as Chief Scientist for the third leg of the journey. This phase of the expedition will in part be characterized by the return of daylight. Even now, there is a perceptible several-hour-long phase of twilight each day, which also makes the cargo transfer a bit easier to manage. Over the next few weeks the sea ice will become even denser, which is why the next exchange, in April, will most likely be done by plane. For this purpose, the snowcats were used to prepare a 900 m long airstrip on the ice. In addition to the flights for exchanging staff and crewmembers, the third leg will also include scientific missions with the research airplanes Polar 5 and Polar 6, which will then be based in Svalbard and are slated to make flights to the still drifting Polarstern.

The expedition in numbers

- From 13 December 2019 to 27 February 2020, the Transpolar Drift carried Polarstern a total distance of 672 km; however, given the meandering course of the drift, the ship only covered a linear distance of 406 km.

- In the same period, the top drift speed, 1.7 km/hour, was reached on 1 February 2020.

- The expedition came within 156 km of the North Pole.

- Using snowcats, engineers created a 900 m long airstrip on the ice.

- On 1 February the air temperature plummeted from an unseasonably warm minus 11.4 degrees to minus 38.2 degrees Celsius, the most intense cold snap observed during this leg of the expedition.

- During the second leg of the journey, the expedition members and crew consumed 8,100 eggs, 1,360 kg of potatoes, and 86 jars of Nutella. Needless to say, that’s not all they ate.

- The longest excursion was a ski tour to an automated monitoring station roughly 10 km from Polarstern. The entire tour was completed in total darkness.

- Only 1 polar bear was sighted during this leg – at night, by an automated camera that just happened to snap a photo while the bear was sniffing the instruments at the remote sensing station.

- Due to fog and a major snowstorm, there were 3 days on which work out on the ice had to be suspended.

- The experts gathered 34.3 terabytes of data.

• 24 February 2020: Four months into the MOSAiC drift campaign, the North Pole is less than 160 km away. Current predictions by international forecast centers and researchers, collected and evaluated by the Sea Ice Drift Forecast Experiment (SIDFEx), suggest that there is a chance that the drift will take the expedition even further North. However, the tight grip of the westward Transpolar Driftstream makes it unlikely that the ship will pass the North Pole in the direction of North America. There is other good news: The probability to get pushed into the open ocean before October 2020 is still not more than 10-15%. 34)

- On Sunday, February 23rd 2020, the MOSAiC expedition onboard the icebreaker RV Polarstern reached 88.5987°N, besting the northernmost point of Fridjof Nansen’s expedition 125 years ago by more than two degrees. While Nansen’s goal was to reach the North Pole, MOSAiCs science plan has no specific interest in this target. Nevertheless, being so close, the question how close to the pole MOSAiC will get is on the mind of participants and observers. Is the camp destined for a continuation of its straight course toward the Fram Strait, named after Nansen’s ship, or could the expedition still pass the pole on the “other side”, across the date line?

Drift forecasts are essential for the planning of expeditions

- When planning the route for his 1893 expedition to reach the North Pole, Nansen had little to go by other than a few pieces of debris from the shipwrecked Jaennette that had been found off the south-west coast of Greenland. After more than a century of research and innovation, planning and execution of science missions such as MOSAiC can now draw on millions of Earth observations and complex weather and climate models running on supercomputers that simulate the evolution of our environment based on the laws of physics. The planning for the MOSAiC drift, in particular where and when to start, relied on satellite observations of Arctic sea ice drift from the previous two decades. This historical information provided a sense of what one might expect for 2019/20. Many months before a planned mission, such climatological information so far remains the best planning tool. This is because modern forecast systems that simulate the ice motion have difficulty adding much skill beyond several weeks forecast lead time. The chaotic nature of the atmosphere makes the winds that drive the ice motion largely unpredictable beyond some point.

- However, when it comes to the drift over the next days to weeks, real-time information from modern forecast systems can sharpen the prediction significantly. These forecasts are useful for mission planning and for applications such as the ordering of high-resolution satellite images of targets moving with the ice. Assessing how well these systems work, how to improve them, and how to best integrate them with historical information to generate seamless forecasts from days to months, is the main motivation for the Sea Ice Drift Forecast Experiment (SIDFEx), an initiative of the Year of Polar Prediction (YOPP). Instead of providing forecasts based on a single system, SIDFEx is bringing together forecasts from more than a dozen systems from many countries, to increase accuracy and to characterize forecast uncertainty.

Sea Ice TickerNr. 23 of 28 February 2020 35)

- Many people following the drift of the MOSAiC expedition are on the edge of their seats; they can’t wait to see just how far north the drift will continue! Careful planning prior to the expedition helped predict how the drift would progress, and which course the MOSAiC camp would follow. This was only possible thanks to numerous drift-route calculations, based on satellite observations, meteorological and climate data from the past 20 years. Yet even with the advanced climate models and supercomputers available today, there’s no 100% guarantee. MOSAiC’s projected drift corridor included potential routes that could take the camp either to the west or east of the North Pole, or ideally right across it.

- During their drift 125 years ago, Fridtjof Nansen and his crew crossed the northernmost parallel at 85° 57’ North on 17th November 1895, roughly 450 km from the North Pole. On 24 February 2020, RV Polarstern reached her northernmost point to date (88° 35’ North), putting her only ca. 150 km from the Pole and significantly closer to Nansen’s goal. However, the latest forecasts indicate that the westward drift will now increasingly be influenced by a southward component, as a result of which the Transpolar Drift will slowly begin taking the MOSAiC camp further from the North Pole and toward Fram Strait. Drifting across the North Pole was never the expedition’s declared goal; rather, it was to improve our understanding of the Arctic climate system and arrive at more accurate reflections of it in global climate models.


Figure 45: MOSAiC is just a a stone’s throw away from the North Pole (image credit: MOSAiC Expedition)

• 16 December 2019: Spare a thought this Christmas for researchers hunkered down on their Polarstern icebreaker, adrift in the frozen Arctic Ocean. Subjected to temperatures as low as –45°C and the perpetual darkness of the polar winter, they are willing participants in MOSAiC – the world’s largest and longest polar research expedition. Despite the darkness, however, the researchers and crew remain aware of what is happening close by. How? With the help of radar imaging satellites. 36)

- After entering the Arctic Ocean in October, the Polarstern has been drifting across the central Arctic at about 7 km per day with the wind and currents expected to carry it close to the geographic North Pole before exiting next spring or summer.


Figure 46: Polarstern shrouded in darkness. The MOSAiC expedition of AWI will make a major contribution to Arctic climate science. During the polar winter, researchers are subjected to temperatures as low as –45°C and the perpetual darkness (image credit: Alfred-Wegener-Institute/Esther Horvath , CC BY-SA 3.0 IGO)

- On board, the scientists are carrying out multiple experiments on the sea ice around the ship to better understand the impact of climate change on sea ice and the Arctic environment. The team has now established hundreds of instruments on the sea ice surrounding the ship within a distance of 50 km.

Figure 47: This animation shows Polarstern’s route and drift as well as the growth of the winter sea ice (image credit: MOSAiC team/US National Snow & Ice Data Center for sea-ice extent) 37)

- Despite the darkness currently enveloping the ship as it drifts through the frozen sea, the researchers and crew are not blind and remain aware of what is happening thanks to radar imaging satellites of Europe’s Copernicus program, Canada, Germany and Japan.

- The crew and scientists monitor the sea ice and generate remarkable maps of the sea-ice floes surrounding the ship. These radar satellites cross the Arctic on a daily basis and carry with them their own source of illumination, which allows them to pierce through the Arctic winter darkness, continuously sensing and mapping the sea-ice conditions below.

- Suman Singha, from the German Aerospace Center’s Remote Sensing Technology Institute, helps coordinate the acquisition of images from different satellites and is responsible for relaying the precious information further to the ship.

- “This information is very much needed at Polarstern, especially at the beginning of the expedition, when the challenge was to find the right kind of ice floe able to harbor both the Polarstern and the deployment of all the scientific instruments on the ice around the ice breaker,” says Dr Singha.

- “Here we made use of high-resolution radar images from the German TerraSAR-X satellite to help locate the best-possible floe, which has since been given the name Fortress. Monitoring the safety of the floe thus remains a constant challenge.”


Figure 48: Radar image from Japan’s ALOS-2 satellite of the sea ice near the Polarstern icebreaker. Polarstern is drifting in the Arctic sea ice for a year for the MOSAiC polar research expedition. During the polar winter, the researchers use radar satellite images such as this to monitor the sea ice in the surrounding area. In this false-color image, which was acquired on 19 November 2019, dark blue cracks show open water leads or thin ice between the ice floes. The white filament-like structures are typically sea-ice ridges or other deformed sea ice (image credit: JAXA)

- Also contributing to the international mapping effort are Europe’s Copernicus Sentinel-1 satellites which provide continual wide-area coverage of the site, helping to follow and predict the ever-changing drift of the sea ice up to 300 km away from the ship.

Figure 49: This video is based on data acquisitions from the Copernicus Sentinel-1 mission between 3 October and 31 October 2019. It remains constantly centered on the Polarstern (bright dot starting at the center of the grid). Polarstern is a German research icebreaker spending a year trapped and drifting in the Arctic sea ice so that scientists from around the world can study the Arctic as the epicenter of global warming and gain fundamental insights that are key to better understand global climate change. The video shows how the initial grid distorts over time by the uneven ice drift over time within the grid array. This results in opening (ice divergence) and closing (ice compression and ridging), shear and vorticity. This shear caused a massive crack to form through the experiment ice floe, disrupting the experiments and forcing movement of some of the instrumentation [video credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by R. Kwok (JPL)]

- The Japanese ALOS-2 satellite with its PalSAR-2 sensor uses a much longer wavelength than both Copernicus Sentinel-1 and TerraSAR-X to map sea-ice floes and conditions below.

- ESA’s Malcolm Davidson said, “Wavelength matters when it comes to radar satellites as a particular wavelength greatly influences the information provided by the satellite.

- “In Europe we are very interested in the additional information that ALOS-2 can provide on sea-ice conditions especially now that we are developing our own long-wavelength radar satellite called the L-band Synthetic Aperture mission, ROSE-L – which is one of the six Copernicus high-priority candidate missions.

- For instance, detecting sea-ice ridges is critical for safe navigation in the Arctic and these are much easier to identify with ALOS-2 than with the existing European satellites.”

- While Polarstern now drifts through the frozen and dark ocean for the coming months, the radar eyes in the sky will continue to monitor its progress through the Arctic and accompany the researchers through the rest of this remarkable expedition.


Figure 50: The researchers participating in the MOSAiC expedition not only have to keep an eye on the ever-changing sea ice, but also on visitors. These polar bears seem to be enjoying playing with the marker flags. Spearheaded by AWI, MOSAiC is the biggest shipborne polar expedition of all time. It involves the Polarstern German research icebreaker spending a year trapped and drifting in the sea ice so that scientists from around the world can study the Arctic as the epicenter of global warming and gain fundamental insights that are key to better understand global climate change (image credit: AWI, Esther Horvath, CC BY-SA 3.0 IGO)

• 18 November 2019: The MOSAiC mission involves 600 people from 19 countries. From a ship trapped in the sea ice, scientists are taking a diverse range of measurements that could help to transform climate models. Carbon Brief’s science writer Daisy Dunne joined the expedition for its first six weeks in the autumn of 2019. This is the first of four articles focused on MOSAiC research. 38)

- Landing a 12-ton helicopter on floating sea ice in the Arctic Ocean is no easy task. But the Russian research crew on this 14-seater Mi-8 have a surprisingly simple trick to make the job easier. As the helicopter approaches the ice, a crew member throws open the door and kicks out an old car tire.

- The crew watch as the tire falls to the ice below. The black of the tire stands in contrast to the grey and bluish tones of the sea ice and the sky above, giving depth to the seemingly flat landscape. This reference point helps the pilots to work out how far they are from the ice surface.

- As the helicopter approaches the ice and hovers just above its surface, Dr Tomasz Petrovsky, a sea-ice specialist from the Arctic and Antarctic Research Institute (AARI) in St Petersburg, jumps out onto the ice and uses a hand drill to burrow through to the ocean below.

- The rest of the research team look on intently. The amount of time it takes to drill through the ice is a good indicator of how thick it is. Petrovsky gives a thumbs up, signalling that the ice is thick enough for the research team to safely get out on the ice and start collecting data.

- In the -6ºC chill, a team of six researchers pile out onto the ice and begin to take more thickness measurements as the helicopter waits nearby. No human has set foot on this chunk of ice before, meaning each step forward poses a potential risk. The ice surface is covered by several centimeters of snow, which could be concealing cracks or stretches of thin ice.

- To navigate the ice safely, the research team keep a close eye on their surroundings. The presence of jagged, tall structures sticking up from the ice surface help the researchers to identify areas of thick ice known as “pressure ridges”. The color of the ice, too, can give an indication of its thickness. Thin ice tends to appear darker in color because it is more translucent and, therefore, shows more of the murky ocean below.

- “Did you see the bear tracks?” Jakob Belter, a sea ice PhD student at the Alfred Wegener Institute (AWI) in Germany, shouts above the whirring of the helicopter blades. Only a couple of meters away, a set of large round paw prints have been left in the snow. Polar bears are widely considered to be one of the largest threats to the safety of scientists on the sea ice. Up ahead, an armed polar bear guard keeps watch of the horizon.


Figure 51: Jan Rohde and Jakob Belter take ice thickness measurements in front of an Mi-8 helicopter in the Central Arctic Ocean (image credit: Daisy Dunne for Carbon Brief)

- The researchers are trying to find chunks of sea ice, known as ice floes, that could be large and thick enough to support a vast array of scientific equipment for an entire year. The chosen ice floes will act as the scaffolding for a network of floating research stations. These stations will play a key role in MOSAiC, one of the largest and most complex Arctic research expeditions ever attempted.

• 16 October 2019: One central task during the first phase of MOSAiC has been completed. Supported by the highly experienced crew and the not less experienced pilots of the MI-8 helicopters, an international team of scientists onboard Akademik Fedorov successfully deployed the so-called Distributed Network. This is the complex system of buoys and measurement instruments that is now drifting in the environs of the central observatory Polarstern in a distance of up to 50 kilometers. 39)

- The larger and smaller sites were partially deployed from aboard the ship, with scientists using the gangway to get access to the ice. In part, they were also deployed on smaller ice floes using helicopters. However, the deployment of the complicated instruments of the Distributed Network on thin and fragile ice presented quite a challenge – a challenge the scientists were also able to take on owing to the wealth of experience and knowledge of the Russian team of AARI sea ice experts.


Figure 52: The international team of scientists onboard Akademik Fedorov successfully deployed the so-called Distributed Network (photo credit: AWI, Mario Hoppmann)

• 04 October 2019: MOSAiC expedition begins its ice drift on a floe at 85 degrees north and 137 degrees east. — After only a few days of searching, experts from the MOSAiC expedition have now found a suitable ice floe, where they will set up the research camp for their one-year-long drift through the Arctic Ocean. Consequently, one of the most important milestones in the expedition has been reached ahead of schedule, and before the Polar Night falls. Nevertheless, the search, which involved satellite imagery, two icebreakers, helicopter flights and scouting missions on the surface of the ice, was an enormous challenge – partly because, after the warm summer, there were very few sufficiently thick floes in the expedition’s start region. 40)

- The die is cast: The MOSAiC team has now selected the floe that will serve as the base of operations for their one-year-long ice drift around the North Pole with the German research icebreaker Polarstern. This was preceded by an intensive search combining satellite imagery and helicopter flights over the target area in the Central Arctic, which were supported by the icebreaker Akademik Fedorov, operated by Russia’s Arctic and Antarctic Research Institute (AARI). The participating researchers closely examined 16 floes that, on the basis of satellite imagery, were potentially large enough to accommodate the ice camp. They subsequently met on board Polarstern to compare their findings, ultimately agreeing that the ice drift should be prepared for on a floe measuring roughly 2.5 by 3.5 km, and located at 85 degrees north and 137 degrees east. The floe, which Polarstern will allow herself to become frozen to, is currently drifting in alternating directions, at up to 10 km/day.

- “After a brief but intensive search, we’ve found our home for the months to come. The ice floe is characterized by an unusually stable area, which we are confident can serve as a good basis and point of departure for establishing a complex research camp. Other parts of the floe are typical of the new Arctic, which is home to thinner, less stable ice. And precisely this combination makes it very well suited to our scientific projects. After carefully reviewing all relevant data, including that from our Russian partners, we came to the conclusion: it may not be the perfect floe, but it’s the best one in this part of the Arctic, and offers better working conditions than we could have expected after a warm Arctic summer,” explains MOSAiC expedition leader Markus Rex of AWI. “We’ll have to wait and see if it’s also stable enough to withstand the autumnal storms that are now brewing. But we’re prepared for all scenarios,” he adds.


Figure 53: Polarstern arrives at a potent ice floe. After comprehensive measurements, the involved scientists decided it to be the MOSAiC ice floe, with the location 85ºN 137ºE on 30 September 2019 (photo credit: AWI, Esther Horvath)

- On 28 September the first researchers from Polarstern set foot on the floe, which had long been a preferred candidate thanks to the promising analyses of the satellite data. On the radar images produced by the satellites, the dark, nearly oval floe stood out thanks to a large, bright region in its northern section. This clearly set it apart from all of the other potential floes, which were consistently dark in the radar images. In the meantime, the experts have dubbed this region ‘the fortress’: made up of highly compressed, several-meter-thick ice, it offers higher stability and a solid basis for the ice camp, which will be erected far above it. In contrast, the darker regions, which are riddled with frozen-over meltwater pools and thin, porous and less stable ice, are typical representatives of the ice conditions in the new Arctic. Here the ice thickness is ca. 30 cm near the freshly frozen-over pools, and between 60 and 150 cm in the older ice between them, although here, too, the bottommost 30 to 40 cm of the ice are extremely porous and less stable.


Figure 54: Polarstern (left) and Akademik Fedorov (right) dock next to each other(photo credit: AWI, Esther Horvath)

- The researchers were unable to determine the floe’s makeup using satellite imagery alone; it took several days and nights of intensive work on the floe itself to gather the requisite data for making a sound choice. In this context, they used an electromagnetic sensor, which they hauled over the ice on foot or with a Skidoo, to map the ice thickness. Ice core samples also yielded data to help assess the ice’s structure. Working in the dark, and in unfamiliar territory, posed a serious challenge. These efforts were coordinated and monitored with infrared cameras from Polarstern’s bridge. Further, members of the expedition’s polar bear patrol accompanied the researchers on the ice to ensure their safety.

- In a final step, a helicopter-mounted laser scanner was used to create a three-dimensional model of the floe’s surface. This map, created during the scouting phase, will help the experts plan the next step: setting up the ice camp. Time won’t be on their side: starting today, the sun will no longer rise over the horizon, and there will only be a few more days with partial light at noon.

- The MOSAiC expedition, spearheaded by AWI, entails a number of unprecedented challenges. The project has an overall budget of ~ 140 million euros. In the course of the one-year-long drift, ~300 experts hailing from 17 countries will be on board. Their common goal: to investigate for the first time the entire climate system in the Central Arctic. To do so, they will gather data on five major aspects – Atmosphere, Sea Ice, Ocean, Ecosystem and Biogeochemistry – in an effort to better understand the interactions that shape the Arctic climate and life in the Arctic Ocean.


Figure 55: First group of scientists lands on an ice floe. Gunnar Spreen (left) and Matthew Shupe (right) examine a potential ice floe for MOSAiC on 30 September 2019, (photo credit: AWI, Esther Horvath)

•21 September 2019: The most ambitious research expedition ever to target the central Arctic got underway as the German icebreaker RV Polarstern pulled out of Tromsø on 20 September 2019, destined for an ice floe where it will serve as a drifting base for hundreds of scientists during the next 13 months. 41)

- More than 10 years after NOAA/CIRES scientist Matthew Shupe of the NOAA ESRL/PSD (Earth System Research Laboratory/Physical Science Division) conceived of the idea, the Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC) has become a $150 million voyage of discovery led by the Alfred Wegener Institute, with significant funding by the US. Department of Energy and other US agencies. More than 400 scientists from 19 countries, including some of the world’s top Arctic researchers, will participate.

- The expedition is led by Germany’s Alfred Wegener Institute (AWI), with key support from the U.S.’s CIRES (Cooperative Institute for Research in Environmental Sciences) at the University of Colorado Boulder and NOAA ERSL/PSD (Earth System Research Laboratory/ Physical Science Division). Overall, 17 nations are involved; the U.S. represents the second largest national contribution with funding support from NOAA, NSF, DOE, and NASA. 42)

- PSD and CIRES scientists have been heavily involved in MOSAiC since the beginning, including developing the initial concept for a year-long, multi-disciplinary project in the Arctic sea ice; playing the chief editorial role for the MOSAiC Science Plan; serving in many leadership roles; implementing multiple science projects; and engaging in outreach and communications activities.

Years of planning help ease a hectic departure

- This is the first time a modern research icebreaker will operate in the direct vicinity of the North Pole year-round, including the nearly six-month long polar night during winter. In terms of the logistical challenges involved, the total number of participants, the number of participating countries, and the available budget, MOSAiC represents the largest Arctic expedition in history. “It’s really amazing to see all the composure here during a really stressful time,” said Shupe, the U.S co-lead on the massive expedition, as dozens of scientists worked to install equipment on board just hours before Polarstern’s departure. “I am really energized by all these people and energy moving in the same direction. I see this around every corner of the ship.”

- Researchers will be conducting experiments and collecting data from the atmosphere, ice and ocean with instruments on board the Polarstern, and from locations up to several miles away, to explore the physical, chemical, and biological processes that drive the Arctic atmosphere, sea ice, ocean, and ecosystem. Results from the mission will help scientists improve models and forecasts of local, regional, and global weather and climate.


Figure 56: Some of the PSD team in Tromsø, Norway, (L-R) Chris Cox, Matt Shupe, Byron Blomquist, Sara Morris (Photo credit: Sara Morris, CIRES)

First challenge: Where do you park an icebreaker?

- After departing Tromsø, 350 miles north of the Arctic Circle, the ship will position itself so that it freezes into drifting ice as the polar night descends. Research during the roughly six months of darkness will present challenges on top of those delivered by the frigid Arctic winter. Special lights, night-vision goggles to watch for polar bears, and activities designed to maintain a healthy daily schedule in the close confines of the ship are some of the adaptations scientists will have to make.


Figure 57: The German icebreaker Polarstern will serve as the hub of a floating base camp for hundreds of scientists studying the Arctic during the year-long expedition. To learn more about the logistics of the mission, visit: (image credit: AWI). The expedition will be resupplied by four icebreakers from Sweden, Russia and China.

- As soon as the Polarstern has dropped anchor at an ice floe, a small city appears on the surface of the ice. Though the MOSAiC researchers don’t live there, it is where they conduct much of their research.

- And they do so using a carefully planned structure: just as blacksmiths, potters and other artisans each had their own district back in the Middle Ages, in the ‘Ice Camp’ meteorologists and climate researchers, marine biologists and specialists for snow, sea ice and other disciplines work together in smaller camps of their own, which are also home to the specific equipment they need.

What happens in the Arctic doesn’t stay in the Arctic

- For the Alfred Wegener Institute’s Markus Rex, leader of the MOSAiC expedition, the Arctic is the “kitchen” for weather in the northern hemisphere. Extreme weather conditions like outbreaks of cold Arctic air in winter, or heat waves in summer, are linked to the changes in the Arctic, he said. Given that Arctic change is likely to have a global impact, research to improve climate models is of utmost importance.

- “There aren’t any reliable prognoses of how the Arctic climate will develop further or what that will mean for our weather,” said Rex. “Our mission is to change that.”

• 20 September 2019: After a decade of preparations, it’s finally time: this evening at 8:30 p.m. the German icebreaker Polarstern will depart from the Norwegian port of Tromsø. Escorted by the Russian icebreaker Akademik Fedorov, she will set sail for the Central Arctic. On board researchers will investigate a region that is virtually inaccessible in winter, and which is crucial for the global climate. They will gather urgently needed data on the interactions between the atmosphere, ocean and sea ice, as well as on the ecosystem. Thanks to the collaboration between international experts, the one-year-long ice drift past the North Pole will take climate research to a completely new level. 43)

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10) Rabe, B, Heuzé, C, Regnery, J, Aksenov, Y, Allerholt, J, Athanase, M, Bai, Y, Basque, C, Bauch, D, Baumann, TM, Chen, D, Cole, ST, Craw, L, Davies, A, Damm, E, Dethloff, K, Divine, DV, Doglioni, F, Ebert, F, Fang, Y-C, Fer, I, Fong, AA, Gradinger, R, Granskog, MA, Graupner, R, Haas, C, He, H, He, Y, Hoppmann, M, Janout, M, Kadko, D, Kanzow, T, Karam, S, Kawaguchi, Y, Koenig, Z, Kong, B, Krishfield, RA, Krumpen, T, Kuhlmey, D, Kuznetsov, I, Lan, M, Laukert, G. Lei, R, Li, T, Torres-Valde s, S, Lin, L, Lin, L, Liu, H, Liu, N, Loose, B, Ma, X, MacKay, R, Mallet, M, Mallett, RDC, Maslowski, W, Mertens, C, Mohrholz, V, Muilwijk, M, Nicolaus, M, O’Brien, JK, Perovich, D, Ren, J, Rex, M, Ribeiro, N, Rinke, A, Schaffer, J, Schuffenhauer, I, Schulz, K, Shupe, MD, Shaw, W, Sokolov, V, Sommerfeld, A, Spreen, G, Stanton, T, Stephens, M, Su, J, Sukhikh, N, Sundfjord, A, Thomisch, K, Tippenhauer, S, Toole, JM, Vredenborg, M, Walter, M, Wang, H, Wang, L, Wang, Y, Wendisch, M, Zhao, J, Zhou, M, Zhu, J., ” Overview of the MOSAiC expedition: Physical oceanography,” Elementa: Science of the Anthropocene 10(1) 2022,

11) ”Climate Change makes Arctic Ozone Loss Worse,” AWI, 23 June 2021, URL:

12) Peter von der Gathen, Rigel Kivi, Ingo Wohltmann, Ross J. Salawitch & Markus Rex, ”Climate change favours large seasonal loss of Arctic ozone,” Nature Communications, Volume 12, 3886 (2021), Published online: 23 June 2021,,


14) Michael Wenger, ”The Polarstern returns home and MOSAiC with it,” Polar Journal, 13 October 2020, URL:

15) ”MOSAiC Arctic expedition reaches North Pole,” ESA Applications, 09 September 2020, URL:

16) ”Time to Say Goodbye —T he MOSAiC floe’s days are numbered, but Polarstern will continue the expedition further north,” AWI, 31 July 2020, URL:

17) ”The latest findings on the MOSAiC floe,” AWI Press Release, 06 July 2020, URL:

18) Thomas Krumpen, Florent Birrien, Frank Kauker, Thomas Rackow, Luisa von Albedyll,Michael Angelopoulos, H. Jakob Belter, Vladimir Bessonov, Ellen Damm, Klaus Dethloff, Jari Haapala,Christian Haas, Carolynn Harris, Stefan Hendricks, Jens Hoelemann, Mario Hoppmann, Lars Kaleschke,Michael Karcher, Nikolai Kolabutin, Ruibo Lei, Josefine Lenz, Anne Morgenstern, Marcel Nicolaus,Uwe Nixdorf, Tomash Petrovsky, Benjamin Rabe, Lasse Rabenstein, Markus Rex, Robert Ricker, Jan Rohde,Egor Shimanchuk, Suman Singha, Vasily Smolyanitsky, Vladimir Sokolov, Tim Stanton, Anna Timofeeva,Michel Tsamados, and Daniel Watkins, ”The MOSAiC ice floe: sediment-laden survivor from the Siberian shelf,” The Cryosphere, Volume 14, pp: 2173–2187, 2020,, Published: 06 Jul 2020, URL:

19) K. Grosfeld, R. Treffeisen, J. Bartsch, et al.,”Map of the MOSAiC Expedition,” AWI Meereisportal, 26 June 2020, URL:

20) ”Polarstern returns to MOSAiC floe — New team continues fieldwork in the Arctic,” AWI Press Release, 18 June 2020, URL:

21) Lisa Grosfeld, ”MOSAiC,” 5 June 2020, URL:

22) Manuel Ernst, ”MOSAiC,” 4 June 2020, URL:

23) ”MOSAiC expedition relief ships arrive in Svalbard to await the Polarstern,” Arctic Today, 26 May 2020, URL:

24) Melinda Webster, ”Notes from the Field,” NASA Earth Observatory, 6 May 2020, URL:

25) ”DFG Supports MOSAiC Expedition in Arctic Ocean During Coronavirus Pandemic,” DFG Press Release No 13, 27 April 2020, URL:

26) Malte Humpert, ”Arctic MOSAiC Expedition Overcomes Logistical Challenges from COVID-19,” High North News, 28 April 2020, URL:

27) ”Alternative resupply plan for Polarstern now in place — Thanks to the support of the German research vessels Merian and Sonne, the MOSAiC expedition will continue, despite the coronavirus pandemic. The new MOSAiC team will start in May,” AWI, 24 April 2020, URL:

28) ”World Press Photo Award for AWI Photographer,” AWI, 17 April 2020, URL:

29) Steven Fons, ”Leads Everywhere,” NASA/GSFC, 20 March 2020, URL:

30) ”MOSAiC aerial survey campaigns for the atmosphere and sea ice temporarily suspended,” AWI Press Release, 16 March 2020, URL:

31) Steven Fons, ”The MOSAiC Floe,” NASA/GSFC, 16 March 2020, URL:

32) Steven Fons, ”Notes from the Field — Farewell to Leg 2—Now Our Work Begins,” NASA/GSFC, 13 March 2020, URL:

33) ”Two New Records at the North Pole. Despite adverse ice conditions, resupply icebreaker reaches the MOSAiC expedition,” AWI, 02 March 2020, URL:

34) Helge Goessling (AWI), Axel Schweiger (Univ. Washington), Thomas Krumpen (AWI), and the SIDFEx Team, ”A Stone’s Throw Away from the North Pole,” MOSAiC, 24 February 2020, URL:

35) ”Sea Ice Ticker Nr. 23: 28 February 2020 MOSAiC now just a stone’s throw away from the North Pole,” MOSAiC, 28 February 2020, URL:

36) ”Shedding light in the dark: radar satellites lead the way,” ESA / Applications / Observing the Earth, 16 December 2019, URL:

37) ”Polarstern route and ice drift,” ESA, 16 December 2019, URL:

38) Daisy Dunne, ”Inside MOSAiC: How a year-long Arctic expedition is helping climate science,” Carbon Brief, 18 November 2019, URL:

39) ”Distributed Network successfully deployed,” AWI Press Release, 16 October 2019, URL:

40) ”A fortress of ice and snow,” AWI Press Release, 4 October 2019, URL:

41) ”A Year Locked in Ice: Unprecedented international expedition to explore the central Arctic gets underway,” 21 September 2019, ERSL/PSD, URL:


43) ”This Evening Sees the Start of MOSAiC – the Greatest Arctic Research Expedition of All Time,” AWI Press Release, 20 September 2019, URL:

The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (

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