Faecal pellets and eggs of Antarctic silverfish have been collected over the seasons using a sediment trap deployed on 1998 in Terra Nova Bay, Ross Sea, Antarctica in the frame of the National Italian Antarctic Research project (PNRA). Antarctic silverfish (ASF) accounts for over 90% of the local fish communities in the Southern Ocean costal area. Samples have been investigated in order to quantify the contribution of fish faecal pellets and eggs to the export of carbon. Funding: CLIMA project (Climatic Long-term Interactions for the Mass Balance in Antarctica) of the Italian National Program for Research in Antarctica.

Zooplankton faecal pellet abundance, volume and flux were determined from samples collected at three stations in the Scotia Sea, Southern Ocean during cruise JR304. Samples were collected at six depths within the 0 - 400 m epi- to upper mesopelagic using Niskin bottles attached to a CTD unit and were preserved in a formalin-based solution. Fluorescence data were collected during the same deployments. Sampling was performed by C. Liszka and G. Tarling on board RRS James Clark Ross. Sample analysis was performed by C. Liszka at British Antarctic Survey in Cambridge.

Piston core PS1506, a repeat of core PS1387, was collected from a midslope bench on the continental margin on the southern limb of the Weddell Gyre in the vicinity of cores PS1388 and PS1389. At these core sites in the Weddell Sea, polynyas enabled continuous primary productivity and benthic life during glacial periods. PS1506 is situated at 2426 m water depth. The core is beneath the depth of the average modern saturation horizon based on the carbonate chemistry of eastern Weddell Sea waters but above the local CCD (carbonate compensation depth).

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)

Results of sediment trap analysis conducted by British Antarctic Survey, University of Edinburgh and University of Bristol. Particulate fluxes and isotopic compositions of particulate organic carbon, nitrogen and biogenic silica are presented. Data from two sediment traps deployed in the Scotia Sea, Southern Ocean, are presented (shallow=400 m, and deep = 2000 m), with 14 samples for each spread across the year 2018 to capture the seasonal cycle from January to December. Each sample was split into multiple fractions for these multiple analyses. Data facilitate the understanding of the magnitude and drivers of particulate fluxes in the Scotia Sea, Southern Ocean. Work funded by NC-ALI funding to the British Antarctic Survey Ecosystems programme. Sian Henley supported by: NE/K010034/1.