Wind profiles from a Galion G4000 Doppler lidar for the international Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) project, derived from conical scans at 30 degree and 50 degree beam elevation angles. The University of Leeds participation in the project- MOSAiC Boundary Layer -was funded by the Natural Environment Research Council (NERC, grant: NE/S002472/1) and involved instrumentation from the Atmospheric Measurement and Observations Facility of the UK's National Centre for Atmospheric Science (NCAS AMOF). This was a year-long project on the German icebreaker Polarstern to study Arctic climate focused on measurements of atmospheric boundary layer dynamics and turbulent structure. The Galion wind profiler provides high resolution (~15m vertical and 5 minute temporal) measurements of wind profiles. Data are only available where sufficient particles are available to backscatter the laser light - in the clean arctic environment, this requires cloud or precipitation.

Particle number flux of airborne snow particles was measured near-continuously at 1-min resolution above the sea ice surface from October 2019 to July 2020 during the year-round MOSAiC expedition. Sensors where mounted at 0.08 m and 10 m on the mast in MetCity on the MOSAiC ice floe drifting during the measurement period within an area of 79.2 N to 88.6 N and 2.7 W to 133.6 E. The SPC measurements were part of the BAS measurement suite during MOSAiC to quantify sea salt aerosol production from blowing snow above sea ice and potential impacts on clouds and climate. Instrument and data quality checks during the year-round campaign were carried out by BAS scientists and the MOSAiC ATMOS team. Funding was provided by UKRI Natural Environment Research Council (NERC) project "Sea Salt Aerosol above Arctic Sea Ice - sources, processes and climate impacts" (SSAASI-CLIM) grant NE/S00257X/1. The project was part of the international Multi-disciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) with the tag MOSAiC20192020.

This dataset contains the floe size distribution (FSD) data derived from high-resolution satellite imagery data acquired at two fixed locations in the Arctic Ocean. Satellite imagery data include MEDEA images and WorldView images. These satellite images have a spatial resolution of 1 m or higher, thus providing the FSD information, especially for small floes. The derived data contain floe size (calliper diameter), shape factor, minor/major axis, perimeter and area of the floes. This dataset has been used to evaluate the sea ice models with the FSD parameterisations. The retrieval of the FSD data was done by the University of Huddersfield team. This work was funded by NERC standard grant NE/R000654/1 and NERC MOSAiC program NE/S002545/1.

20 Ice Trackers were deployed at the MOSAiC drifting site. The deployment of the trackers was made from the helicopter onboard RV Polarstern during Leg 5 of the expedition. The data contain the GPS positioning of the trackers (and the motion of the ice on which the trackers were deployed). The data record starts from early September 2020 and lasted until July 2021 for the longest-surviving trackers. The trackers started their drift near the North Pole and move to the south through the Fram Strait. The deployment of the trackers was done in collaboration with the MOSAiC ice team. This work was funded by NERC MOSAiC program NE/S002545/1.

Calanus hyperboreus dominates the copepod biomass in the high Arctic. It forms an important intermediate trophic level in the Central Arctic food web, grazing on algae and protists and serving as prey for a large range of other zooplankton, fish and seabirds. Their unique lipids (20:1, 22:1 fatty acids and fatty alcohols) can be traced within the Arctic megafauna from seals to whales and polar bears, as these energy-rich lipids are crucial body reserves for the dark season. During the MOSAiC expedition in the Central Arctic Ocean (CAO, 2019-2020), C. hyperboreus adult females (AF) and subadult copepodites stages (CV) were sampled weekly to fortnightly. A range of nets were used to sample either horizontally underneath the sea ice or vertically from maximum 2000 m through the water column. Onboard, ~10 AF and ~20 CV of C. hyperboreus were sorted from each catch, photographed, rinsed with freshwater to remove salt and frozen at -80C for subsequent analysis of their total dry mass (DM), lipid content and a suite of trophic markers, including bulk stable isotopes (BSI), phytosterols (PS), total fatty acids (TFA), total fatty alcohols (TFAlc), and highly-branched isoprenoids (HBI). During the time of their seasonal descent at the end of summer, vertical sampling of C. hyperboreus was intensified and additional parameters were analysed, e.g. the FA and FAlc composition of their storage lipids (neutral lipids, NLFA, NLFAlc) and membrane lipids (polar lipids, PLFA, PLFAlc), the carbon isotopic composition of key FA and FAlc (CSIA-FA; CSIA-FAlc), and the tissue density. By combining this array of trophic markers, valuable information about the body conditions and feeding history of these copepods can be linked to their life cycle and vertical distribution. The initial separation of the various trophic markers was carried out at the University of Plymouth. After estimating the total DM, subsamples for BSI were sent to the Littoral, Environment and Societies Joint Research Unit stable isotope facility (CNRS - University of La Rochelle, France) for analysis. Three internal standards were added to the samples used for lipid analysis to quantify the TFA, TFAlc, PS and HBI content. As a first step, the total lipid content of the animals was extracted in dichloromethane : methanol. The lipid samples were split into two equal subsamples, one was sent to the Alfred-Wegener-Institute (AWI) in Bremerhaven/Germany for FA and FAlc analyses and the second was used for PS and HBI analyses in Plymouth. This dataset is linked to a manuscript that compares the trophic marker composition of C. hyperboreus from the surface vs. deep ocean to understand drivers, benefits, and risks of their seasonal migration in the CAO. The manuscript focusses mainly on the copepod descent in late summer and the changes in body conditions and trophic marker composition over the winter months. Contributions by KS were funded by the UK's Natural Environment Research Council MOSAiC Thematic project SYM-PEL: "Quantifying the contribution of sympagic versus pelagic diatoms to Arctic food webs and biogeochemical fluxes: application of source-specific highly branched isoprenoid biomarkers" (NE/S002502/1). CJA, RGC, CEG, KMS and RJ were funded by the US National Science Foundation Office of Polar Programs (OPP-1824447 and OPP-1824414).

This dataset contains the floe size distribution (FSD) data derived from multi-satellite imagery data acquired across the Arctic Ocean. Satellite imagery data includes high-resolution visible images from the USGS Global Fiducials Library (MEDEA), TerraSAR-X/TanDEM-X and Worldview-3 (WV3). The derived data contain floe size (calliper diameter), shape factor, minor/major axis, perimeter and area of the floes. This data set has been used to investigate the characteristics of the FSD during major seasonal evaluation stages of Arctic sea ice floes. The retrieval of the FSD data was done by the University of Huddersfield team. This work was funded by NERC MOSAiC program NE/S002545/1.

During the MOSAiC expedition in the Central Arctic Ocean (CAO, 2019-2020), POM was sampled weekly to fortnightly from surface waters and the Chlorophyll a maximum layer (Chl a max) via CTD casts and from bottom sea ice of the floe via ice coring (first- and second-year ice, two layers nearest to the water-ice interface). The POM was filtered onboard (GF/F filters) and deep frozen for the subsequent analysis of a suite of lipid biomarkers, including IP25 and other highly-branched isoprenoids (HBI), fatty acids (FA) and sterols. These biomarkers can provide valuable information about the nutritional value, the taxonomic composition (e.g. diatoms vs flagellates), and the origin of the POM that represents the basis of the Central Arctic food web. This dataset comprises the results from the HBI analysis only, while the FA dataset is already published and the sterol data will be submitted shortly. The separation of the various lipid biomarkers was carried out at the University of Plymouth. After addition of internal standards for each of the 3 components, the filters were saponified with KOH. Thereafter, non-saponifiable lipids (HBI and sterols) were extracted with hexane and purified by open column chromatography (SiO2). Fatty acids were obtained by adding concentrated HCl to the saponified solution and re-extracted with hexane. The analysis of IP25 was carried out using an Agilent 7890A gas chromatograph (GC), coupled to an Agilent 5975 mass selective detector (mass spectrometry, MS), fitted with an Agilent HP-5ms column with auto-splitless injection and helium carrier gas. Identification of IP25 and other HBIs was achieved by comparison of their individual GC retention indices and mass spectra with those obtained from purified standards. IP25 was quantified by, first, integrating individual ion responses in selected-ion monitoring mode (m/z 350.3), second, normalising these to the corresponding peak area of the internal standard and, third, applying an instrumental response factor obtained from a purified standard. These IP25 quantities per filter can be normalised to the volume of filtered seawater or melted ice core water. Contributions by KS were funded by the UK's Natural Environment Research Council MOSAiC Thematic project SYM-PEL: ''Quantifying the contribution of sympagic versus pelagic diatoms to Arctic food webs and biogeochemical fluxes: application of source-specific highly branched isoprenoid biomarkers''/ (NE/S002502/1)

This dataset contains the post-processed GNSS/INS buoy data for a kinematic correction of a moving base station. The GNSS/INS buoys were deployed on sea ice during the 2019-20 MOSAiC expedition. These buoys recorded raw GNSS/INS data at a sampling rate of 10 Hz. For the kinematic correction, two buoys (with overlapping measurements of each other) were selected, and one of the buoys was used as a moving "base" and the other as the "rover". The post-processed dataset contains kinematically corrected latitude, longitude and velocity of the rover, as well as the baseline distance between the rover and base. The main objective of the kinematic correction is to create high-precision and high-frequency data to measure ice dynamics at a few centimetre accuracies. The buoys were assembled by the University of Huddersfield team and the deployment was done by the MOSAiC ice team throughout the expedition. This work was funded by NERC MOSAiC program NE/S002545/1.

This dataset contains the raw data from GNSS/INS (Global Navigation Satellite System/Inertial Navigation System) buoys deployed during the 2019-2020 MOSAiC expedition. These buoys recorded the data from GNSS and Sensors. The raw GNSS data contain time, latitude, longitude, velocity, and fix type. The raw Sensors data contain time, acceleration, gyroscope, magnetometer, and temperature. These data were sampled at 10 Hz. The original data was in ANPP format (see advancednavigation.com), which have been converted to structured ASCII formats (such as RINEX, CSV) using Spatial Manager software. The buoys were assembled by the University of Huddersfield team and the deployment was done by the MOSAiC ice team throughout the expedition. This work was funded by NERC MOSAiC program NE/S002545/1.

This data set provides processed Ku- and Ka-band fully-polarimetric backscatter and derived polarimetric parameters from hourly scans, acquired using the KuKa radar, during Legs 1, 2, 4 and 5 of the 2019-2020 MOSAiC International Arctic Drift Expedition. Scans were acquired during winter (Legs 1 and 2), advanced melt (leg 4) and freeze-up (Leg 5) seasons, from various Remote Sensing (RS) sites, located in the MOSAiC ice floe. The first deployment of the KuKa radar was on 18 October 2019 at RS1 site and the radar was retreated (due to ice break up) on 18th November. The radar was redeployed on 29th November at RS2 site until 13th December when cracks were observed at the site and the instrument was turned off and moved to a safe location. The radar was redeployed at RS3 site and started measuring again on 21st December 2019 until 31st January 2020, after which the radar was taken off the RS site to conduct maintenance. The radar was not operational during Leg 3. During Leg 4, the radar was operational between 25th June and 19th July 2020, and later retreated back to the ship, for deployment in Leg 5. The radar was deployed on 24th August 2020 and operational until the end of the MOSAiC expedition. The dataset was collected by MOSAiC Team ICE participants and processed by Vishnu Nandan at the University of Manitoba, Canada. This work was funded in part through NERC grant NE/S002510/1, the Canada 150 Chair Program and the European Space Agency PO 5001027396. The authors thank Marine Environmental Observation, Prediction and Response Network (MEOPAR) Postdoctoral Fellowship grant to Vishnu Nandan. The authors also thank the crew of R/V Polarstern and all scientific members of the MOSAiC expedition for their support in field logistics and field data collection. ***** PLEASE BE ADVISED TO USE VERSION 2.0 DATA ***** The VERSION 2.0 data set (see 'Related Data Set Metadata' link below) has been corrected for a bug that was found in the original KuKa radar processing chain.