Overview of the MOSAiC expedition: Physical oceanography

Arctic Ocean properties and processes are highly relevant to the regional and global coupled climate system, yet still scarcely observed, especially in winter. Team OCEAN conducted a full year of physical oceanography observations as part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), a drift with the Arctic sea ice from October 2019 to September 2020. An international team designed and implemented the program to characterize the Arctic Ocean system in unprecedented detail, from the seafloor to the air-sea ice-ocean interface, from sub-mesoscales to pan-Arctic. The oceanographic measurements were coordinated with the other teams to explore the ocean physics and linkages to the climate and ecosystem. This paper introduces the major components of the physical oceanography program and complements the other team overviews of the MOSAiC observational program. Team OCEAN’s sampling strategy was designed around hydrographic ship-, ice- and autonomous platform-based measurements to improve the understanding of regional circulation and mixing processes. Measurements were carried out both routinely, with a regular schedule, and in response to storms or opening leads. Here we present along-drift time series of hydrographic properties, allowing insights into the seasonal and regional evolution of the water column from winter in the Laptev Sea to early summer in Fram Strait: freshening of the surface, deepening of the mixed layer, increase in temperature and salinity of the Atlantic Water. We also highlight the presence of Canada Basin deep water intrusions and a surface meltwater layer in leads. MOSAiC most likely was the most comprehensive program ever conducted over the ice-covered Arctic Ocean. While data analysis and interpretation are ongoing, the acquired datasets will support a wide range of physical oceanography and multi-disciplinary research. They will provide a significant foundation for assessing and advancing modeling capabilities in the Arctic Ocean

Overview of the MOSAiC expedition: Physical oceanography

Arctic Ocean properties and processes are highly relevant to the regional and global coupled climate system, yet still scarcely observed, especially in winter. Team OCEAN conducted a full year of physical oceanography observations as part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), a drift with the Arctic sea ice from October 2019 to September 2020. An international team designed and implemented the program to characterize the Arctic Ocean system in unprecedented detail, from the seafloor to the air-sea ice-ocean interface, from sub-mesoscales to pan-Arctic. The oceanographic measurements were coordinated with the other teams to explore the ocean physics and linkages to the climate and ecosystem. This paper introduces the major components of the physical oceanography program and complements the other team overviews of the MOSAiC observational program. Team OCEAN’s sampling strategy was designed around hydrographic ship-, ice- and autonomous platform-based measurements to improve the understanding of regional circulation and mixing processes. Measurements were carried out both routinely, with a regular schedule, and in response to storms or opening leads. Here we present alongdrift time series of hydrographic properties, allowing insights into the seasonal and regional evolution of the water column from winter in the Laptev Sea to early summer in Fram Strait: freshening of the surface, deepening of the mixed layer, increase in temperature and salinity of the Atlantic Water. We also highlight the presence of Canada Basin deep water intrusions and a surface meltwater layer in leads. MOSAiC most likely was the most comprehensive program ever conducted over the ice-covered Arctic Ocean. While data analysis and interpretation are ongoing, the acquired datasets will support a wide range of physical oceanography and multi-disciplinary research. They will provide a significant foundation for assessing and advancing modeling capabilities in the Arctic Ocean

Expendable Conductive-Temperature-Depth (xCTD) data from MOSAiC leg 5 north of Greenland

Xctd (Expendable Conductive-Temperature-Depth) data were collected north of Greenland during MOSAiC leg5, when R/V Polarstern was relocated north between leg4 and leg5. The data were collected mid-August 2020. The data contained temperature, salinity and pressure from the surface to 500 m depth. The data are despiked and corrected from a salinity offest of 0.03. The data were collected by team OCEAN during leg 5 ( Zoe Koenig, Mario Hoppmann, Salar Karan and Jacob Allerholt) at the aft of the ship

Unprocessed seawater temperature, conductivity and salinity transmitted by CTD buoy 2020O10 in the Arctic Transpolar Drift in 2020/21 as part of the MOSAiC Leg 5 (PS122/5) buoy deployments

An ice-tethered buoy system (2020O10) carrying 5 CTDs was deployed by RV Polarstern in the central Arctic Ocean in August 2020 as part of MOSAiC Leg 5 (PS122/5). The buoy was equipped with 5 Seabird SBE37IMP Microcat CTDs mounted along an 100m long inductive modem tether at depths of 10, 20, 50, 75 and 100m. The buoy was installed close to the main buoy site in the central observatory of Leg 5, and co-located with multiple Snow Buoys, Ice Mass Balance Buoys and other, more complex instruments. The surface unit of the buoy prompted the instruments for a measurement of temperature, conductivity/salinity and pressure every 10 minutes. The data was then transmitted to a base station via iridium along with GPS position and time, as well as surface temperature. After a several months long drift through the central Arctic Ocean and Nordic Seas, the buoy was recovered in Húnaflói, Iceland in October 2022. This entry explicitly only includes the 10-minute data transmitted by the buoy itself. A processed and quality controlled version of this dataset, combined with the recovered 2-minute data from the individual CTDs, will be provided and linked to upon completion

Physical oceanography measurements from a hand-held CTD during Leg 4 and 5 of POLARSTERN cruise PS122 – MOSAiC

This dataset contains hydrographic data collected with a small hand-held conductivity, temperature, depth sensor (CTD, a Sea&Sun CTD48M) – mostly operated from the ice – during Leg 4 and Leg 5 of the Multidisciplinary drifting observatory for the study of Arctic climate (MOSAiC). In total, 24 profiles were obtained, 12 from each leg. The data collected was processed manually. Conductivity readings below 0.5 mS/cm and temperature readings below the surface freezing temperature were removed. A pressure offset was then subtracted to start the profile at 0 dbar. The data was then binned in steps of 0.1 dbar from the surface to 5 dbar, in steps of 0.25 dbar to 20 dbar, and in steps of 0.5 dbar below. Large density inversions were manually removed and linearly interpolated over. Absolute Salinity (SA) and Conservative Temperature (CT) were derived using the TEOS-10 GSW toolbox (McDougall & Barker, 2011). This work was carried out as part of the international Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) with the tag MOSAiC20192020. We thank all persons involved in the expedition of the Research Vessel Polarstern during MOSAiC in 2019-2020 (AWI_PS122_00) as listed in Nixdorf et al. (2021)

Videos and extracted frames from Blueye ROV camera during MOSAiC Leg 4 (PS122/4) and Leg 5 (PS122/5)

Videos and extracted frames from Blueye ROV camera during MOSAiC Leg 4 (PS122/4) and Leg 5 (PS122/2). During Leg 4, images were taken in a lead and under level ice on 07.07.2020 when the ice floe was located in the western Fram Strait (81 37N, 4 17E). The footage shows an algae layer at the interface between the freshwater lens, originating from meltwater at the surface, and the more saline ocean water below. During leg 5, images were taken in a lead and under level ice on 12.09.2020 in the Amundsen Basin (88 46N, 100 24E). These images show platelet ice at the base of the ice

Overview of the MOSAiC expedition: Physical oceanography

Arctic Ocean properties and processes are highly relevant to the regional and global coupled climate system, yet still scarcely observed, especially in winter. Team OCEAN conducted a full year of physical oceanography observations as part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), a drift with the Arctic sea ice from October 2019 to September 2020. An international team designed and implemented the program to characterize the Arctic Ocean system in unprecedented detail, from the seafloor to the air-sea ice-ocean interface, from sub-mesoscales to pan-Arctic. The oceanographic measurements were coordinated with the other teams to explore the ocean physics and linkages to the climate and ecosystem. This paper introduces the major components of the physical oceanography program and complements the other team overviews of the MOSAiC observational program. Team OCEAN’s sampling strategy was designed around hydrographic ship-, ice- and autonomous platform-based measurements to improve the understanding of regional circulation and mixing processes. Measurements were carried out both routinely, with a regular schedule, and in response to storms or opening leads. Here we present along-drift time series of hydrographic properties, allowing insights into the seasonal and regional evolution of the water column from winter in the Laptev Sea to early summer in Fram Strait: freshening of the surface, deepening of the mixed layer, increase in temperature and salinity of the Atlantic Water. We also highlight the presence of Canada Basin deep water intrusions and a surface meltwater layer in leads. MOSAiC most likely was the most comprehensive program ever conducted over the ice-covered Arctic Ocean. While data analysis and interpretation are ongoing, the acquired datasets will support a wide range of physical oceanography and multi-disciplinary research. They will provide a significant foundation for assessing and advancing modeling capabilities in the Arctic Ocean

Raw data files recorded by CTD buoy 2020O10 in the Arctic Transpolar Drift in 2020/21 as part of the MOSAiC Leg 5 (PS122/5) buoy deployments

An ice-tethered buoy system (2020O10) carrying 5 CTDs was deployed by RV Polarstern in the central Arctic Ocean in August 2020 as part of MOSAiC Leg 5 (PS122/5). The buoy was equipped with 5 Seabird SBE37IMP Microcat CTDs mounted along an 100m long inductive modem tether at depths of 10, 20, 50, 75 and 100m. The buoy was installed close to the main buoy site in the central observatory of Leg 5, and co-located with multiple Snow Buoys, Ice Mass Balance Buoys and other, more complex instruments. The individual instruments were programmed to record oceanographic data internally at 2-minute intervals. The surface unit of the buoy prompted the instruments for an additional measurement every 10 minutes, which was then transmitted to a base station via iridium along with GPS position and time, as well as surface temperature. After a several months long drift through the central Arctic Ocean and Nordic Seas, the buoy was recovered in Húnaflói, Iceland in October 2022. As a result, the internally recorded 2-minute data from the CTDs could also be secured. The attached zip archive comprises the unprocessed 10-minute data transmitted by the buoy, the 2-minute data downloaded and converted from the 5 individual CTDs after their recovery, as well as selected auxiliary information. A processed and quality controlled version of this dataset will be provided and linked to upon completion

Raw data of GPS position and sea-surface temperature recorded by 44 Southtek NOMAD drifting buoys in the marginal ice zone north of Svalbard in 2022

44 Southtek Iridium GPS drifters of types Offshore NOMAD-T V3 (33) and Offshore NOMAD V2 (11) were deployed in the marginal ice zone northwest of Svalbard as part of RV Polarstern expedition PS131 (ATWAICE) in July-August 2022. In addition to GPS position and time, the 33 NOMAD-T buoys also measured sea-surface temperatures. The 44 buoys were used for a total of 48 individual deployments, including 4 redeployments of recovered instruments, to either mark and track non-iridium instruments (6), to mark important sites (2), to track individual ice floes (1), or to elucidate the surface ocean currents as a complement to measurements obtained by the towed Triaxus system (31) or the ship-based CTD (8). The buoys were either thrown over board into open water, placed on sea ice, or attached to instruments. The measurement and transmission intervals were between 1 hour and 15 minutes, and were also partly reconfigured during operation. The drifter data were downloaded directly on board and displayed in the ship's Mapviewer software in near-real time, to facilitate navigation and to support the scientific program in decision-making. The attached .zip archive contains the original data files obtained from the Southtek server, which were partially modified to account for the 4 redeployments (indicated by "redeployed" in the filename), and to fill a data gap caused by an iridium data provider issue (indicated by "merged" in the filename). The files still include the deck test data, which needs to be removed according to the attached table with deployment metadata (including deployment time and position)

Raw and converted full-resolution data from ocean microstructure measurements using an MSS profiler during the Polarstern PS131 cruise, ATWAICE

Ocean microstructure profiles were collected using an MSS (Microstructure Sensor Profiler, Sea&Sun Technology, Germany) profiler during the Polarstern PS131 cruise, ATWAICE (28 June – 17 August 2022), from ice floes and from the ship. This dataset includes 1) the raw binary data in the instrument-specific MRD files and 2) the full-resolution time series from each channel converted into physical units with no further data processing applied (NetCDF, NC files). A set of two files (MRD and NC) is supplied per profile. The converted data are prepared following the SCOR Working Group ATOMIX guidelines and convention, corresponding to their Level 1. In total, 196 raw data files (cast004 to 199) are submitted. Casts 1 to 3 were from another profiler which flooded and the data are not useful. Out of 196 profiles, 16 were collected from the ship and 180 from sea ice. Of the 196 profile attempts, 10 were aborted, but all files are delivered for completeness. Please see the detailed log spreadsheet for stations and comments in the NC files. Throughout the cruise, the instrument functioned well, except the vibration sensor did not work and the fast thermistor channel produced a cut-off at low end, probably for output that exceeded the range of the A/D converter of the probe. In the later part of the cruise, episodic data transmission errors were encountered. The profiler used was MSS90L (SN 097), a loosely-tethered free-fall instrument equipped with two airfoil probes aligned parallel to each other, a fast-tip thermistor (FP07), an acceleration sensor (for body vibration measurements), conventional CTD sensors for precision measurements, a Turner Design Cyclops-7 in Vivo Chlorophyll/Blue sensor for ChlA fluorescence and a SST-DO, fast optical dissolved oxygen sensor. All channels were sampled at 512 Hz. The instrument was ballasted for a typical fall speed of 0.5 m s-1. The shear probes used were type PNS6, serial numbers C6258 (sensitivity 3.54e-04 at 21C, SHE1) and C6259 (sensitivity 3.99e-4 at 21C, SHE2). A temperature correction for the sensitivity was applied using the average in situ temperature, TM, as (1-0.011*(TC-TM)), where TC=21C. The same sensors were used throughout the cruise and the sensors point downward when the instrument profiles vertically. The deployment of the MSS from the ship was done from the starboard side. Because of the keel of the ship, the upper 15 m of dissipation rate profiles from the ship should be excluded in post-processing. The deployment from sea ice was typically by using a Nansen sled, through a hole, located approximately 100 -250 m away from the ship. The upper 2 m of the dissipation profiles from ice should be excluded in post-processing