Raw (calibrated as per Demer et al., 2015) Simrad EK60 echosounder data (18, 38 and 120 kHz; Kongsberg Maritime, Norway) collected annually in August and September between 2011 and 2016 as part of the Barents Sea Ecosystem Survey (Eriksen et al., 2018) were obtained from the Norwegian Marine Data Centre (Institute of Marine Research, Norway). The data were used to evaluate the StrathE2EPolar (an end-to-end food web model incorporating ice-dependencies to simulate climate-fisheries interactions in the Barents Sea) model. Echosounder data were calibrated and processed (noise removed). Nautical-area-scattering coefficient (NASC, m2 nmi-2: average received echo energy over a given depth range scaled up to a square nautical mile) values were computed between 15 m (maximum vessel draft plus echosounder near-field for all surveys, vessels and frequencies) and 400 m (lower extent of StrathE2EPolar model domain). NASC values at 18 kHz were used as a proxy for fish biomass. NASC values at 120 kHz and where NASC 120 kHz > 38 kHz > 18 kHz were used as a proxy for macro-zooplankton biomass. NASC values were binned into a 0.5 by 0.5-degree grid and averaged to map the spatial distribution of fish and macro-zooplankton. Funded by NERC project Microbes to Megafauna Modelling of Arctic Seas (MiMeMo), NE/R012571/1 (lead), and NE/R012679/1.

The data include size, sex, location and morphological measurements and of Muraenolepis specimens included in Fitzcharles et al. (2021). The morphometric data were primarily collected from fish captured during South Georgia Groundfish Surveys in 2003, 2004 and 2005, with additional data obtained from type specimens and extracted from published descriptions of Muraenolepididae. For genetic studies, tissue samples from the South Georgia specimens were supplemented by additional tissue samples from Muraenolepis in other parts of the Southern Ocean. Source, location and depth of capture are included for all specimens that were sequenced, together with sequence Accession Numbers (to the DNA Database of Japan) for Cox 1 and 16S rRNA sequences. The work was primarily funded by the Government of South Georgia & the South Sandwich Islands and was a component part of Elaine Fitzcharles'' PhD (University of St Andrews).

Acoustic backscatter data were collected on board the RRS James Clark Ross during cruise JR19001 on 10/12/2019 in Stromness Harbour and South Georgia. Data were collected using a Simrad EK60 echosounder at 38, 70, 120 and 200 kHz. The EK60 was calibrated on 09/12/2019 in Stromness Harbour, South Georgia. More information about the calibration can be found in the Cruise Report for JR19001. This work was carried in the frame of the Polar Ocean Ecosystem TimeSeries - Western Core Box (POETS-WCB) project.

Temperature data were collected from a tidepool at Rothera Point, Antarctica every two minutes from February 1999 to May 2000, with the aim of documenting tidal, diurnal and seasonal variability.

This data set represents the model results plotted in the figures in Bett et al. (2024), produced using the MITgcm/WAVI ice/ocean coupled model. The model domain is the Amundsen Sea sector, where the simulations start in approximately the year 2015 and run for 180 years. Simulations are forced using idealised ocean boundary conditions which represent cold and warm conditions, along with a third extreme case where no ice shelf melting is applied. These simulations were produced in order to examine the ice/ocean processes that occur during future evolution of the region. For full descriptions of the results plotted in each figure see Bett et al. (2024). Funding was provided by NERC Grant NE/S010475/1, ITGC THWAITES MELT (NE/S006656/1), ITGC THWAITES PROPHET (NE/S006796/1) and the European Union''s Horizon 2020 grant PROTECT (869304).

Acoustic backscatter data were collected on board the RRS Sir David Attenborough during polar science trials 2023 (cruise SD025) on 25/02/2023 in Admiralty Bay, King George Island, Antarctica. Data were collected using a Simrad EK80 echosounder at 18, 38, 70, 120, 200 and 333 kHz. The EK80 was calibrated on 10/03/2023 in the Weddell Sea. This work was supported by NERC core funding to BAS.

Acoustic backscatter data were collected on board the RRS James Clark Ross during cruise JR17002 on 20/01/2018 in Bransfield Strait and the caldera of Deception Island. Data were collected using a Simrad EK60 echosounder at 38, 70, 120 and 200 kHz. The EK60 was calibrated on 07/01/2018 in Stromness Harbour, South Georgia. More information about the calibration can be found in the Cruise Report for JR17002. This work was carried in the frame of the Polar Ocean Ecosystem TimeSeries - Western Core Box (POETS-WCB) project.

Marine debris washed up on beaches on Goudier Island has been recorded since 2014. Surveys are conducted on a monthly basis when the station is occupied during the summer season. This data contributes to the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) Marine Debris programme.

Macrozooplankton and nekton were collected with a Rectangular Midwater Trawl 25 (RMT25) over several visits to the sustained observation location P3 (52.70 S, 40.26 W) in the northern Scotia Sea during November and December 2017. The work was carried out as part of the NERC Large Grant, COMICS (Controls on Mesopelagic Interior Carbon) on board the RRS Discovery (cruise DY086). The RMT25 net hauls sampled between 10 and 500 m depth, with the water column divided into 2 depth intervals (10-250 m and 250-500 m). A total of 6 hauls were obtained during 3 separate visits to station P3, each visit comprising a pair of hauls, of which one was carried out in nominal daytime and the other in nominal nighttime. Catches were immediately sorted on board and identified to the lowest taxonomic level feasible. Subsamples of the catches were retained, principally for subsequent biochemical and physiological analyses. In total, 777 fish were caught, belonging to at least 23 species, with catches dominated by the myctophids Krefftichthys anderssoni, Gymnoscopelus braueri, Electrona antarctica and Protomyctophum tenesoni. The water column below 250m was dominated by Bathylagus spp. Temperate myctophid species, such as Protomyctophum parallelum and Protomyctophum andreyeshevi were also caught in small numbers. With regards macrozooplankton, the 250m-500m depth interval was dominated by the jellyfish, Atolla and Periphylla. The tunicate Salpa thompsoni and the euphausiids Euphausia triacantha and Thysanoessa spp. were also relatively abundant. Jellyfish still dominated catches in shallower waters (250m-10m), closely followed by euphausiids and Salpa thompsoni and chaetognaths. Themisto gaudichaudii and Parandania boecki were the most numerous amphipod species caught. Decapods were only caught in the deeper depth interval, both day and night.

An opportunistic marine mammal survey through the Atlantic Ocean between the UK and Antarctica was undertaken in November and December 2020. The RRS James Clark Ross, was used to transfer cargo and personnel for the British Antarctic Survey (BAS) from the UK to Rothera Research Station, Antarctica for the start of the 2020/2021 summer season. The transit and station relief included stops at King Edward Point and Bird Island, South Georgia, Falkland Islands and Signy Research Station, South Orkney Islands. The journey took a total of 48 days. Two JNCC marine mammal observers were on-board as well as other dedicated observers. Marine mammal observations were made as opportunistic sightings and recorded along with geographical position and other metadata. This transit and subsequent survey was unique in its passage as few vessels journey down the centre of the North and South Atlantic and continue on down the Western Antarctic Peninsula. British Antarctic Survey will continue to make this journey twice a year and it could provide a platform for an annual marine mammal survey of the entire Atlantic Ocean.