Description: During RV MS Merian expedition MSM75, an international, multidisciplinary team explored the Reykjanes Ridge from June to August 2018. The first area of study, Steinahóll (150–350 m depth), was chosen based on previous seismic data indicating hydrothermal activity. The sampling strategy included ship- and AUV-mounted multibeam surveys, Remotely Operated Vehicle (ROV), Epibenthic Sledge (EBS), and van Veen grab (vV) deployments. Upon returning to Steinahóll during the final days of MSM75, hydrothermal vent sites were discovered using the ROV Phoca (Kiel, GEOMAR). Here we describe and name three new, distinct hydrothermal vent site vulnerable marine ecosystems (VMEs); Hafgufa, Stökkull, Lyngbakr. The hydrothermal vent sites consisted of multiple anhydrite chimneys with large quantities of bacterial mats visible. The largest of the three sites (Hafgufa) was mapped, and reconstructed in 3D. In total 23,310 individual biological specimens were sampled comprising 41 higher taxa. Unique fauna located in the hydrothermally venting areas included two putative new species of harpacticoid copepod (Tisbe sp. nov. and Amphiascus sp. nov.), as well as the sponge Lycopodina cupressiformis (Carter, 1874). Capitellidae Grube, 1862 and Dorvilleidae Chamberlin, 1919 families dominated hydrothermally influenced samples for polychaetes. Around the hydrothermally influenced sites we observed a notable lack of megafauna, with only a few species being present. While we observed hydrothermal associations, the overall species composition is very similar to that seen at other shallow water vent sites in the north of Iceland, such as the Mohns Ridge vent fields, particularly with peracarid crustaceans. We therefore conclude the community overall reflects the usual “background” fauna of Iceland rather than consisting of “vent endemic” communities as is observed in deeper vent systems, with a few opportunistic species capable of utilizing this specialist environment.

Description: The Ægir Ridge System (ARS) is an ancient extinct spreading axis in the Nordic seas extending from the upper slope east of Iceland (∼550 m depth), as part of its Exclusive Economic Zone (EEZ), to a depth of ∼3,800 m in the Norwegian basin. Geomorphologically a rift valley, the ARS has a canyon-like structure that may promote increased diversity and faunal density. The main objective of this study was to characterize benthic habitats and related macro- and megabenthic communities along the ARS, and the influence of water mass variables and depth on them. During the IceAGE3 expedition (Icelandic marine Animals: Genetics and Ecology) on RV Sonne in June 2020, benthic communities of the ARS were surveyed by means of a remotely-operated vehicle (ROV) and epibenthic sledge (EBS). For this purpose, two working areas were selected, including abyssal stations in the northeast and bathyal stations in the southwest of the ARS. Video and still images of the seabed were usedtoqualitatively describebenthic habitats based on the presence of habitat-forming taxa and the physical environment. Patterns of diversity and community composition of the soft-sediment macrofauna, retrieved from the EBS, were analyzed in a semiquantitative manner. These biological data were complemented by producing high-resolution bathymetric maps using the vessel’s multi-beam echosounder system. As suspected, we were able to identify differences in species composition and number of macro- and megafaunal communities associated with a depth gradient. A biological canyon effect became evident in dense aggregates of megafaunal filter feeders and elevated macrofaunal densities. Analysis of videos and still images from the ROV transects also led to the discovery of a number ofVulnerable Marine Ecosystems (VMEs) dominated by sponges and soft corals characteristic of the Arctic region. Directions for future research encompass a more detailed, quantitative study of the megafauna and more coherent sampling over the entire depth range in order to fully capture the diversity of the habitats and biota of the region. The presence of sensitive biogenic habitats, alongside seemingly high biodiversity and naturalness are supportive of ongoing considerations of designating part of the ARS as an “Ecologically and Biologically Significant Area” (EBSA).

Description: Peracarid abundance and composition were studied in the Atlantic Sector of the Southern Ocean and the Weddell Sea at a depth range of 403-2021 m. Samples were collected using an epibenthic sledge (EBS) during expeditions on board the RRS James Clarke Ross in the Filchner Trough (JR275), the South Orkney Islands (JR15005), the Prince Gustav Channel (JR17003a) and on board the RV Polarstern in the Eastern Antarctic Peninsula (PS118). Expeditions took place in February-March 2012, 2016, 2018 and 2019 respectively. Since the trawling distance between stations was not always the same, in order to make data comparable between different stations, numbers of individuals were standardized to 1000 m haul distances. In total 64766 peracarids were found and sorted into five different orders (Amphipoda, Cumacea, Isopoda, Mysidacea and Tanaidacea). Amphipods were the most abundant group representing the 32% of the total abundances. The Filchner Trough had the highest abundance of peracarids, while the South Orkney Islands showed the lowest abundance compared to other areas.

Description: Multibeam data were collected during RRS James Clark Ross cruise JR17003a (2018-02-22 to 2018-03-12). Multibeam sonar system was Kongsberg EM122. Data are unprocessed and may contain outliers and blunders and should not be used for grid calculations and charting projects without further editing. The raw multibeam sonar data in Kongsberg multibeam processing format (*.all) were recorded with Kongsberg SIS software running on Windows operating system. Kongsberg data files can be processed using the software packages CARIS HIPS/SIPS or with the open source software package MB-System.

Description: Multibeam data were collected during RRS James Clark Ross cruise JR17003a (2018-02-18 to 2018-03-12). Multibeam sonar system was Kongsberg EM 122 multibeam echosounder. Data are processed with Caris HIPS, including sound velocity correction with SV data from CTDs and World Ocean Atlas 09, tidal correction with TPXO9_atlas_v5 (https://www.tpxo.net/global/tpxo9-atlas), and manual cleaning. The soundings are combined in daily files, the format is XYZ ASCII (〈Lon〉 〈Lat〉 〈Depth in meters, positive up, relative to mean sea level〉). Additional blockmedian grids have been computed with depth dependent cell size to visualize the data. These grids are not meant for scientific analysis or navigation, but for overview purposes only.

Description: This dataset provides metadata of Antarctic deep-water sponges (Demospongiae and Hexactinellida) and sediment collected for microbiome analysis during expeditions PS96 (RV Polarstern, 2015/16) and JR17003a (RRS James Clark Ross, 2018) in the Weddell Sea. It includes information on sampling locations, number of bacterial sequences and amplicon sequence variants (ASVs), NCBI accession numbers for raw sequencing data, and SMF collection numbers for the sponges archived in the collection of Senckenberg Museum, Frankfurt am Main, Germany.

Description: This dataset provides metadata of bottom water samples collected for microbiome analysis during expeditions PS96 (RV Polarstern, 2015/16) and JR17003a (RRS James Clark Ross, 2018) in the Weddell Sea, Antarctica, as well as environmental data of the respective stations. It includes information on sampling locations, number of bacterial sequences and amplicon sequence variants (ASVs), and NCBI accession numbers for raw sequencing data. Environmental data of PS96 stations were obtained from: Schröder, Michael; Ryan, Svenja; Wisotzki, Andreas (2016): Physical oceanography measured on water bottle samples during POLARSTERN cruise PS96 (ANT-XXXI/2 FROSN). Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, PANGAEA, https://doi.org/10.1594/PANGAEA.859035

Description: Sponges (Porifera) host diverse and species-specific communities of microbial symbionts with which they maintain tight interactions. However, knowledge on the microbiomes of sponges from deep waters and remote polar areas is still scarce, especially for the sponge class Hexactinellida. Therefore, our aim was to describe the community composition, richness and density of microbial symbionts of Antarctic deep-water sponges, including several species of hexactinellids, and relate the findings to host ultrastructure and histology. During the Antarctic expeditions PS96 (RV Polarstern, 2015/16, eastern Weddell Sea) and JR17003a (RRS James Clark Ross, 2018, western Weddell Sea), 28 sponge specimens, bottom water and sediment were sampled for molecular analysis of microbial communities. The sponges were collected from deep habitats of 290-845 m by Bottom Trawl or Agassiz Trawl and comprised 19 hexactinellids and 9 demosponges. Bottom water was collected with a CTD rosette sampler which also measured environmental data (temperature, salinity, oxygen) close to the start or end point of the trawls and at four additional stations. Sediment was collected from the Agassiz trawl together with sponge samples during JR17003a. The molecular microbiome analysis targeted bacteria and was based on 16S rRNA gene sequencing of the V3-V4 variable regions. Sequences were processed using the QIIME2 environment. Amplicon sequence variants (ASVs) were generated with the DADA2 algorithm and classified based on the Silva 132 99% OTUs 16S database. Eight sponge specimens collected during JR17003a were further investigated microscopically for microbial symbionts, sponge histology and ultrastructure. Histological sections of 7-30 µm were stained in either Masson's trichrome or Hematoxylin/Eosin and images captured on a Zeiss Axioskop 2 plus with a QiCam camera using Northern Eclipse software. Ultrastructural sections of 60 nm were stained in uranyl acetate and lead citrate and then viewed and photographed with a Philips Morgagni transmission electron microscope equipped with a Gatan CCD camera. This Data Collection includes sampling information, environmental data, NCBI accession numbers and photographs of the analyzed sponges, data on the microbial symbiont communities (amplicon sequence variants and microbial phyla) of sponges, seawater and sediment, as well as micrographs of sponge histology and ultrastructure.

Description: The marine-based West Antarctic Ice Sheet (WAIS) is considered vulnerable to irreversible collapse under future climate trajectories, and its tipping point may lie within the mitigated warming scenarios of 1.5° to 2°C of the United Nations Paris Agreement. Knowledge of ice loss during similarly warm past climates could resolve this uncertainty, including the Last Interglacial when global sea levels were 5 to 10 meters higher than today and global average temperatures were 0.5° to 1.5°C warmer than preindustrial levels. Using a panel of genome-wide, single-nucleotide polymorphisms of a circum-Antarctic octopus, we show persistent, historic signals of gene flow only possible with complete WAIS collapse. Our results provide the first empirical evidence that the tipping point of WAIS loss could be reached even under stringent climate mitigation scenarios.