Description: Measuring temperature and salinity profiles in the world's oceans is crucial to understanding ocean dynamics and its influence on the heat budget, the water cycle, the marine environment and on our climate. Since 1983 the German research vessel and icebreaker Polarstern has been the platform of numerous CTD (conductivity, temperature, depth instrument) deployments in the Arctic and the Antarctic. We report on a unique data collection spanning 33 years of polar CTD data. In total 131 data sets (1 data set per cruise leg) containing data from 10 063 CTD casts are now freely available at doi:10.1594/PANGAEA.860066. During this long period five CTD types with different characteristics and accuracies have been used. Therefore the instruments and processing procedures (sensor calibration, data validation, etc.) are described in detail. This compilation is special not only with regard to the quantity but also the quality of the data – the latter indicated for each data set using defined quality codes. The complete data collection includes a number of repeated sections for which the quality code can be used to investigate and evaluate long-term changes. Beginning with 2010, the salinity measurements presented here are of the highest quality possible in this field owing to the introduction of the OPTIMARE Precision Salinometer.

Description: Glass sponges (Porifera, Hexactinellida) are important structuring components of the benthos in Antarctic shelf regions. They can grow up to 2 m in height and form extensive sponge beds in some areas, dominating the benthic biomass and providing habitat for a variety of other animals. However, much of their ecology is still unknown to date, including the factors determining their distribution and abundance. In the current study, we investigate glass sponge distribution and abundance in the south-eastern Weddell Sea in relation to environmental factors (water mass characteristics, currents, ice cover), as well as food availability and abundance of predators. During two recent expeditions with RV Polarstern in 2013/14 and 2015/16, we collected photos and videos of the ocean floor by using different gear equipped with HD cameras: an Ocean Floor Observation System (OFOS), a Remotely Operated Vehicle (ROV), and a multi grab (MG). For each of 28 stations, 30 images are selected and analysed for abundance and species composition of glass sponges and their predators, as well as substrate characteristics. In addition to that, we measured temperature, salinity, concentrations of dissolved and particulate silicon, and bacterial cell numbers. Furthermore, model and/or satellite data on current strength, mean annual ice cover and chlorophyll a concentration as a proxy for productivity will be included in the study. Glass sponge abundance will be analysed in relation to the environmental data and predator abundance in order to identify the factors determining the abundance and distribution of glass sponges in the south-eastern Weddell Sea. Our findings will provide an important baseline to assess how glass sponge communities might change in a changing Antarctic environment.

Description: Ice in its different forms affects benthic communities in Polar Regions directly and indirectly. In order to recognize effects of ice on benthic communities we analyzed benthos in four regions of the Weddell Sea: a) the southeastern Weddell Sea shelf (SEWSS); b) the Filchner-Rønne Outflow System (FROS); c) the Larsen A/B embayments; and d) the tip of the Antarctic Peninsula. These regions differ considerably in their ice regimes: The SEWSS is a typical high Antarctic habitat, influenced by seasonal sea ice coverage; the FROS is influenced by seasonal ice on its eastern edge, but under heavy year round ice conditions on its western edge; the Larsen A/B embayments were covered for hundreds of years by thick ice shelves, which recently disintegrated providing large areas for recolonization by benthos; and the shelf around the tip of the Antarctic Peninsula which can be considered as being unaffected by ice. Benthos in these four regions revealed distinct differences in abundance, biomass, and production values. Highest abundance values were found at the tip of the Antarctic Peninsula and along the SEWSS (2,767 and 2,535ind.m-2, respectively), whereas the lowest abundance corresponded to the Larsen A/B region (682ind.m-2). In terms of both, biomass and production, the southeastern Weddell Sea region showed the highest values (3,944.2g wet weight.m-2 and 10.3g C.y-1m-2, respectively), whereas the lowest values were found at Larsen A/B (71.08g.m-2 and 1.62g C.y-1.m-2) and FROS regions (71.08g.m-2 and 1.62 g C.y-1.m-2). A PERMANOVA showed the differences among regions to be significant in all three terms: abundance (Pseudo F=7.10; p=0.001), biomass (Pseudo F=6.01; p=0.001), and production (Pseudo F=6.28; p=0.001). These differences were mainly caused by sponges, ophiuroids and polychaetes. This study also shows pronounced differences in the structure, composition of the benthic communities in the four regions. We hypothesize that these differences are primarily due to the different sea-ice regimes in the regions.