Collection and preservation of open ocean water samples from stations along a transect in the Barents Sea over the course of a year from July 2017 - July 2018. Four cruises in total to cover seasonal changes, two on board the James Clark Ross (RRS) and two aboard the Helmer Hansen (RV). A standard CTD cast was deployed to collect the samples, the depths were selected to support Primary Production experiments on board the ship, with deep samples representing 1% PAR. Research assistants from SAMS (Scottish Association for Marine Science) were responsible for the sample collection and Elaine Mitchell of SAMS was responsible for the sample analysis and data processing. This work was funded by Arctic PRIZE - NERC Thematic grant - Changing Arctic Ocean (CAO) programme - NE/P006302/1.

Morphometric data were collected for 417 Calanus finmarchicus copepods (stage CV), swimming activity data were collected using locomotor activity monitors for 469 Calanus finmarchicus copepods (stage CV) and oxygen consumption activity data were collected using a Loligo microplate respirometry system for 40 Calanus finmarchicus copepods (stage CV). All data were collected in the Fram Strait, Arctic Ocean, from two stations (F7 and D6) in August 2019, coinciding with the timing of early diapause in this species. Photographs were taken and experiments were conducted onboard RRS James Clark Ross. The data are reported in detail in Grigor et al., Torpidity as an indicator of overwintering diapause in Calanus finmarchicus. Funding was provided by the CHASE project (NE/R012733/1), part of the Changing Arctic Ocean (CAO) programme, jointly funded by the UKRI Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF). Sampling and experiments were performed on the DIAPOD cruise to the Fram Strait in August 2019.

Collection and preservation of open ocean water samples from stations along a transect up the east coastline of Greenland and then across the Fram Strait to Svalbard during May 2018 & August 2019. Two cruises in total to cover annual changes, both on board the James Clark Ross (RRS). A standard CTD cast was deployed to collect the samples, depths were surface and the chlorophyll maximum, selected to support zooplankton net sampling and other on board experiments. Research assistants from SAMS (Scottish Association for Marine Science) were responsible for the sample collection on JR17-005, Dave Pond of Stirling University was responsible for collection on JR18-007. Elaine Mitchell of SAMS was responsible for the sample analysis and data processing. Funding was provided by the DIAPOD - NERC Thematic grant - Changing Arctic Ocean (CAO) programme - NE/P006213/1

Collection and preservation of open ocean water samples from stations along a transect up the east coastline of Greenland and then across the Fram Strait to Svalbard during May 2018. The cruise was to observe spring bloom conditions, on board the RRS James Clark Ross. A standard CTD cast was deployed to collect the samples, depths were surface, the chlorophyll maximum and a deep sample, selected to support zooplankton net sampling and other on-board experiments. Research assistants from SAMS (Scottish Association for Marine Science) were responsible for the sample collection on JR17005, Elaine Mitchell of SAMS was responsible for the sample analysis and data processing. Funding was provided from the DIAPOD - NERC thematic grant - Changing Arctic Ocean programme - NE/P006280/1.

Concentrations of dissolved and atmospheric nitrous oxide, N2O, were measured in the austral spring of 1992 in the Drake Passage and Bellingshausen Sea as part of the United Kingdom Joint Global Ocean Flux Study expedition to the Southern Ocean. The measured atmospheric mixing ratio was 313 +/- 5 parts per billion by volume, in agreement with the hemispherically corrected global mean. In the Drake Passage, surface N2O saturations were generally very close to atmospheric equilibrium, 99.7 +/- 3%, although several anomalous points were associated with the presence of frontal and eddy-like features within the Antarctic Polar Frontal Zone and at the Continental Water Boundary. Further to the south, a series of oceanographic stations and two surface transects along the 85 degrees W meridian between 65.28 degrees S and 70.32 degrees S revealed a transition from undersaturated conditions in open water to oversaturated conditions in the marginal ice zone, in the upper mixed layer (75-100 m). These observations reflect upwelling of Circumpolar Deep Water at approximately 70 degrees S, resulting in the accumulation of N2O under the winter sea ice and its subsequent release to the atmosphere following the ice retreat. Sea-air N2O fluxes were estimated from the product of the surface N2O anomaly and the modelled gas transfer coefficients of Liss and Merlivat [1986] and Wanninkhof [1992] to find a maximum rate of +3.1 micromole N2O m-2 d -1. North of the upwelling region, Antarctic Surface Water formed from the mixing of surface waters and ice melt was moderately depleted in N2O with respect to the atmosphere, a minimum 90% of saturation. This sink area was estimated to extend between 65.28 degrees S and 69.57 degrees S with a mean sea-air flux of between -0.6 +/- 0.4 and -0.9 +/- 0.7 micromole N2O m-2 d-1. The region studied at 85 degrees W (65.28 degrees S to 70.32 degrees S) revealed source and sink areas which were largely determined by the changing physical hydrography, so that overall there was a small net negative flux of between -0.06 +/- 0.9 and -0.09 +/- 1.4 micromole N2O m-2 d-1. Funding: The work was supported by NERC funding to the Plymouth Marine Laboratory, the British Antarctic Survey and from the U.K. Biogeochemical Flux Study (BOFS).

Bulk elemental (carbon and nitrogen) and stable isotope (delta 13C and delta 15N) data produced from 491 samples collected between 2016-2021 from terrestrial (soil, peat, living biomass, dead biomass), intertidal (saltmarsh vegetation, saltmarsh roots, seagrass biomass, mudflat, faecal matter) and marine (macroalgae, microalgae zooplankton, finfish aquaculture waste) environments across the UK. These samples alongside analytical standard derived from natural materials (lignin, humic acid, cellulose, glucose, protein) were analysed to determine their bulk elemental (organic carbon and nitrogen) and stable isotope (delta 13C org and delta 15N) composition. These values are envisioned to be used to constrain organic carbon sources (terrestrial vs marine) in the natural environment when used alongside isotope mixing models. The work was carried out under the NERC programme - Carbon Storage in Intertidal Environment (C-SIDE), NERC grant reference NE/R010846/1. Full details about this dataset can be found at https://doi.org/10.5285/a445a7a8-528d-4e0b-9094-28cbcd449367

To further our understanding of Antarctic predator growth and seasonal physiology, field growth rates were measured for two soft-bodied Antarctic anemone benthic predators, Isotealia antarctica and Urticinopsis antarctica, using in situ sampling of anemones on uniquely marked tiles from Rothera Research Station from 2020-2023. Ex situ measurements of oxygen consumption and seven-day faecal output were obtained from recently collected specimens in aquaria and compared between summer and winter. Winter physiological data for Antarctic species are rare, and we tested the hypothesis that generalist feeders or predators continue to feed during the winter. There is a dearth of basic life history and physiological data from Southern Ocean species, particularly from benthic sessile predators. This is an important data gap because species inhabiting the Southern Ocean live in a more temperature stable but seasonally varying environment than temperate and tropical counterparts. This work was supported by core funding from the NERC, UKRI, UK to the British Antarctic Survey.

Mesozooplankton were collected with a MOCNESS net system during the oceanographic cruise JR17005 (May and June 2018) and JR18007 (August 2019). The MOCNESS comprised 9 separate nets which opened in sequence such that the closing of one net opened the next; net 1 was open during the descent of the net to its maximum depth (about 1000 m) while the remaining 8 depths opened at regular intervals during the reascent to the surface. Catches were immediately preserved in 4 percent buffered formaldehyde after division by a Folsom splitter into either 0.5 or 0.25 fractions. Identification of taxa was performed by Continuous Plankton Recorder survey analysts at the Marine Biological Association UK, led by Marianne Wootton. Specimens were categorised to the lowest possible taxonomic level, which, in some cases, encompassed developmental stages but, in other cases, was limited to higher order taxa. Each taxa was enumerated to determine abundance with the preserved fraction of the catch. These were scaled up to the whole catch and divided by the volume filtered of the respective net to determine abundance in units of individuals m-3. These values were also multiplied by the sampled depth interval to derive the alternative unit of individuals m-2. The samples from three net deployments were analysed from both JR17005 and JR18005 in approximately matching locations between Greenland and Svalbard, encompassing the Fram Strait. The dataset allows examination of the distribution and abundance of these species across the region in two separate years, with the first year covering early summer and the second year, late summer. Financial support for was provided by Changing Arctic Ocean (CAO) Programme DIAPOD, funded by UKRI Natural Environment Research Council (NERC; NE/P006213/1, NE/P006353/1, NE/P006302/1, NE/P006183/1,and NE/P005985/1, amongst others), and by CAO Project CHASE, jointly funded by NERC (NE/R012733/1) and the German Federal Ministry of Education and Research (BMBF; 03F0803A).

A seasonal cycle of the FA composition of particulate organic matter from surface waters, Chlorophyll-a maximum layer and bottom sea ice, sampled during the MOSAiC expedition in the Central Arctic Ocean (2019-2020), suggests the importance of phylogenetic and environmental drivers. To improve our understanding of these different drivers, we conducted culture experiments with 32 cold-water algal strains where temperature, light intensity, and nutrient supply were manipulated individually or in combination. The culture experiments were carried out at the Culture Collection of Algae and Protozoa (CCAP; Oban, Scotland), the Roscoff Culture Collection (RCC; Roscoff, France) and the Alfred-Wegener-Institute-Helmholtz-Centre for Polar and Marine Research (AWI; Bremerhaven, Germany). The strains were part of the culture collections, had been isolated in the Arctic (25 strains), Southern Ocean (2 strains) or North Atlantic (5 strains), and included diatoms, chlorophytes, haptophytes, cryptophytes, chrysophytes, dinoflagellates and cyanobacteria. Some of the species are Arctic sea ice diatoms (e.g. Nitzschia frigida, Attheya spp.) or pelagic diatoms (e.g. Thalassiosira gravida), while others are non-diatom species that are becoming increasingly prominent in the Arctic, e.g. the coccolithophore Emiliania huxleyi (synonym Gephyrocapsa huxleyi), the prymnesiophyte Phaeocystis pouchetii, the chlorophyte Micromonas spp. and the cyanobacterium Synechococcus spp.. The experiments can be divided into three groups: First, those that tested a low light-low temperature setting, second, those that tested a low light-low temperature and a higher light-higher temperature setting and, third, those that tested the effect of nutrient (nitrate, phosphate and silicate) shortage in combination with low and high light intensity. The first set of experiments was conducted with all 32 strains, the second set with all strains grown at CCAP and AWI, and the third set focuses on the keystone under-ice diatom Melosira arctica. The experiments were run for 4-7 weeks to accumulate sufficient biomass for biomarker extractions (FA and sterols), C:N analysis and light-microscopy of cell size and cell concentration. At the end of the experiments, the algae were filtered onto GF/F filters and deep frozen until analysis. After addition of internal standards for FA and sterols, the filters were saponified with KOH. Thereafter, non-saponifiable lipids (sterols) were extracted with hexane and purified by open column chromatography on silica gel. FA were obtained by adding concentrated HCl to the saponified solution and re-extracted with hexane. Samples were converted into fatty acid methyl esters (FAME) and analysed using an Agilent 6890N gas chromatograph with FID detector. The Clarity chromatography software system (DataApex, Czech Republic) was used for chromatogram data evaluation. FAME were quantified via the internal standard, Tricosanoic acid methyl ester (23:0) (Supelco, Germany) to provide the total amount of FA (TFA) per filter. These FA datasets of cultured algae are presented in a manuscript together with the FA pattern seen in sea ice- and water column POM in the CAO during the MOSAiC expedition and in previously published data from Arctic shelf regions. The manuscript focusses mainly on two important long-chain omega-3 FA (eicosapentaenoic acid and docosahexaenoic acid) that are considered essential for the nutrition of higher trophic levels, including humans, and their production to decline with global temperature rise. 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). CRM was funded by the NERC National Capability Services and Facilities Programme (NE/R017050/1).