MOSAiC Expedition
The Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition was a one-year-long expedition into the Central Arctic. For the first time a modern research icebreaker was able to operate in the direct vicinity of the North Pole year round, including the nearly half year 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.
During its one-year-long journey, the central expedition ship, the research icebreaker Polarstern from Germany's Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, was supported and resupplied by the icebreakers and research vessels Akademik Fedorov and Kapitan Dranitsyn, Sonne and Maria S. Merian and Akademik Tryoshnikov. In addition, extensive operations involving helicopters and other aircraft were planned. In total, during the various phases of the expedition, more than 600 people were working in the Central Arctic. The international expedition, which involved more than 80 institutions from 20 countries, was conducted by the AWI and was led by the polar and climate researcher Markus Rex and co-led by the atmospheric researcher Matthew Shupe from the University of Colorado Boulder. MOSAiC's main goals were to investigate the complex and still only poorly understood climate processes at work in the Central Arctic, to improve the representation of these processes in global climate models, and to contribute to more reliable climate projections.
The expedition cost 140 million euros ; half of the budget was provided by the German Federal Ministry of Education and Research. U.S. participation was primarily supported by the National Science Foundation, which contributed roughly $24 million to the project, among the largest Arctic research initiatives the agency has ever mounted. The U.S. Department of Energy was also highly invested in the mission, funding nearly $10 million and providing the largest suite of atmospheric instruments.
The MOSAiC expedition
In the half-year-long Arctic winter, the sea ice is too thick for research icebreakers to penetrate. Consequently, data from the Central Arctic is virtually non-existent, particularly during winter. For reaching the Central Arctic in winter, the MOSAiC expedition followed in the footstep of Fridtjof Nansen's famous expedition with the wooden sailing ship Fram in the years 1893–1896, over 125 years ago. His daring voyage showed that it was possible to let a ship drift across the polar cap, from Siberia to the Atlantic, stuck in the thick sea ice and solely driven by the forces of the natural drift of the ice. Though Nansen has demonstrated the fundamental feasibility of such an endeavour, the scientific measurements possible in his days were still quite rudimentary. During MOSAiC, for the first time the FramThe heart of MOSAiC was the Polarstern
After delivering one last load of fuel, at the end of October Akademik Fedorov returned to Tromsø. From this point on, the natural drift carried Polarstern and its network of research stations across the North Pole region. On 24 February 2020, the Polarstern has broken a record: during the drift she reaches 88°36' North, just 156 kilometres from the North Pole. In summer 2020, the ship reached the Fram Strait. On 13 August, after a last big refueling and personnel rotation, Polarstern started steaming towards the Central Arctic to study the onset and early freezing phase of the sea ice. On 19 August, the ship reached the North Pole. The journey from the northern Fram Strait to the Pole only took six days to complete. After a short search, the MOSAiC team found a new ice floe. The so-called MOSAiC floe 2.0 was discovered eleven nautical miles from the route that the original floe took in January 2020. Polarstern left the MOSAiC floe 2.0 on 20 September 2020, one year after the start of the expedition. On 12 October 2020, the Polarstern returned to her homeport in Bremerhaven.
During the period August/September 2020, the German research aircraft Polar 5 and Polar 6 took off from Spitsbergen to conduct aerial surveys of the sea ice and atmosphere over the Arctic Ocean, supplementing the MOSAiC expedition's research programme.
Fuel depots set up on islands off the coast of Siberia specifically for the expedition supported potential emergency operations by long range helicopters, which were able to reach Polarstern in the event of an emergency at least during the early and late phases of the expedition.
Research focus areas
The primary goal of the MOSAiC project is to understanding the coupled climate processes in the Central Arctic, so that they can be more accurately integrated into regional and global climate models. The findings will contribute to more reliable climate projections for the Arctic and globally, to improved weather forecasts and better Arctic sea ice forecasts.In addition, the outcomes of the MOSAiC mission will help to understand the regional and global effects of Arctic climate change and the loss of sea ice. They will improve the preparedness of communities in the Arctic and northern mid-latitudes, provide the scientific basis for the development of policies for a sustainable development of the Arctic and support fact based decision-making in the areas of mitigation of and adaptation to global climate change.
Atmosphere
The comprehensive and complex atmospheric measurements carried out during MOSAiC provide a physical basis for understanding local and vertical interactions in the atmosphere and the interactions between the atmosphere, the sea ice, and the ocean. The characterization of processes in clouds, in the atmospheric boundary layer, surface layer, and surface energy flux will lead to a better understanding of the lower troposphere, which interacts with the surface in the Arctic. Performed heat flux measurements allowed for an accurate estimate of the surface skin temperature, which showed a substantial bias of those measurements in comparison with uncoupled atmospheric reanalyses. One of the greatest challenges was carrying out these measurements consistently throughout the sea ice's entire annual cycle, especially at the beginning of the freezing period, so as to monitor the transition from open water to a very thin ice layer. Readings taken at higher altitudes provided insights into the characteristics of the middle and upper troposphere and the interaction with the stratosphere. To improve our understanding of aerosols and aerosol-cloud interactions over the Central Arctic, especially in winter, measurements were taken on the composition of the particles, their physical properties, their direct and indirect radiation effects, and their interactions with cloud properties. Routine radiosonde observations in combination with tethered balloon measurements provided high-resolution profiles of the atmospheric conditions in the column of air above the MOSAiC site. In addition, radar measurements were used to determine the vertical profile of wind speed and direction as well as key cloud properties, including ice and liquid water content. Key thermodynamic parameters, as well as the kinematic structures of the atmosphere, were investigated with the aid of microwave and infrared radiometers, Raman and Doppler lidar.Snow and sea ice
The sea-ice observations covered the broad range from the physical and mechanical characteristics of Arctic sea ice, to its morphology, optical properties and mass balance. The emphasis was on characterising snow cover and ice cover, and on arriving at a better understanding of the processes that determine their properties. Snow trenches and ice cores helped the researchers gather this valuable data. Further aspects of the sea ice observation included determining the mass budget by measuring the depth of snow cover and ice thickness, as well as measuring the diffusion of sunlight in the ice, the ice's spectral albedo, and its transmission. In addition, various types of ice were monitored throughout the entire annual cycle in order to determine the spatial variability and development of ice cover in the Arctic over time.Ridge observations revealed that the most of first-year ridge consolidation occurred during the spring season before the melt onset, and was initiated by warm air intrusions and transfer of snow into leads, which was also confirmed by 6%–11% snow mass fraction in ridges. It was also shown, that bottom melt rates for pressure ridges were approximately four times larger than for level ice, while ridge shape also influenced its melt, with higher melt for deeper, steeper, and narrower ridges. The observations included measurements of snow density, mechanical resistance, and microstructure, which allowed to compute snow thermal conductivity. Ice mass balance observations included the installation of buoys measuring sea ice temperature, as well as ablation stakes, measuring the evolution of sea ice surface and bottom interfaces. Additionally, sea ice thickness was measured using ground-based electromagnetic sounding, while snow and sea ice freeboard were measured using helicopter-based laser scanner. Additionally, underwater sea ice topography and other physical parameters were measured using observations from remotely operated vehicle, as well as biophysical characterization of algae habitats. Winter observations were characterized by the presence of platelet ice due to the presence of supercooled water, while summer melt was characterized by meltwater stratification and formation of false bottoms which covered around 20% of sea-ice area. Aerial observations of surface temperature revealed a strong 41% preconditioning of surface melt ponds, which form in the areas of warm surface temperature anomalies in winter, typical for thin ice and snow.