Description: Total lipid and fatty acid concentrations were studied in a late spring-early summer flagellate-dominated bloom in the Weddell Sea. These indicators were considered a good tool for assessing the quality of organic matter settling from surface to deep-water layers (epibenthic water layers). The results showed different patterns between the early (11-15 December 2003) and the late sampling period (18-27 December 2003) at all studied depths (5 m, 50 m and near-bottom water layers). Low phytoplankton biomass (mainly flagellates) in the first half of the study corresponded to low total lipid and fatty acid concentrations. In the second sampling period a spring bloom (mainly flagellates and diatoms) was detected, increasing the total lipid and fatty acid concentrations in the water column. The amount of settling organic matter from surface waters to the near-bottom water layers was high, especially in the late sampling period. Trophic markers showed evidence of a sink of available organic matter rich in quality and quantity, especially in terms of polyunsaturated fatty acids, for benthic organisms from surface layers to bottom layers in only a few days. The importance of studying short-time cycles in order to detect organic matter availability for benthic biota in view of the pulse-like dynamics of primary production in Antarctic waters is discussed.

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: Due to extreme pack ice, the Filchner Region in the southern Weddell Sea is one of the least studied regions on the planet. Here, we provide a detailed description of the benthic communities of this high-Antarctic ecosystem, and assess the relationship between environmental factors and benthic distribution patterns. Fieldwork was performed in the austral summers of 2013-14 and 2015-16 during the R/V ‘Polarstern’ cruises PS82 and PS96. Using a combination of multibox corer (MBC) and seabed image data from 37 stations (water depths 243-1217 m), we differentiated 6 station groups. While 1 of these groups was comprised of a single station, the other 5 groups represented distinct benthic communities. Three of these correspond to the previously described Eastern Shelf, Southern Shelf, and Southern Trench communities. However, we found distribution shifts and MBC abundance and biomass reductions when comparing our results with earlier studies. The other 2 groups have novel characteristics and are presented here as an Ice/Ice Shelf Water-related community and a Continental slope community. Water depth in combination with 2 or 3 other environmental variables (out of 7 available) explained 〈30% of the benthic distribution and composition. We found a tighter relationship between water mass circulation and spatial distribution of the communities; we suggest using water-mass-related characteristics (e.g. productivity regimes, water currents) to better explain benthic spatial distribution patterns.

Description: Trophic structure is among the most fundamental characteristics of an ecosystem since it is a useful way to determine the main energy flow at the ecosystem level. In the Magellan Strait, the local spatial heterogeneity at the shallow-waters ecosystems may have a great variety of potential food sources; however, knowledge about their biological communities and their structure is still unclear. We examined the trophic structure of shallow-water-mixed bottom communities at two sites in the sub-Antarctic Magellan Strait based on carbon (d13 C) and nitrogen (d15 N) stable isotope ratios. The benthic communities were composed of 46 species from 20 major taxa at Bahı´a Laredo (BL) and 55 species from 18 major taxa at Punta Santa Ana (PSA). Benthic macroalgae and organic matter associated with sediment are the major primary food sources at both sites. Although both sites are quite similar in their food sources and in their vertical trophic structure (C three trophic levels), the food web structure varied distinctly. Functionally, predators and grazers dominated both communities, but top predators were shorebirds, carnivore anemones and predatory nemerteans at BL, and sea stars, shorebirds, crabs and fishes at PSA. The distinct differences in the trophic structure at BL and PSA highlight the important variability of d15 N at the base of the benthic food web, the role of local environmental conditions and community dynamics in structuring shallow-water communities.

Description: Complex marine-terrestrial interactions characterize Chilean fjords, where benthic communities influence the distribution of organic matter (OM). We examined spatial and seasonal changes in the hydrography, sediment conditions and soft-bottom macrobenthic, meiobenthic, and total microbial biomass in a glacial Patagonian fjord (Martinez Channel, Chile). The transport of a high load of glacial mineral and particulate OM to the fjord in the austral summer coincided with low total live benthic biomass. Multivariate analysis evidenced temporal-related macrofaunal groups influenced by the different environments produced by the advection of sediment transport and terrestrial OM from the Baker River, Chile. The relationships between density/biomass and respiration versus body size varied considerably with distance from major riverine inputs, but the slopes of density size spectra and normalized biomass size spectra were less negative in summer than in winter. Occasional large-scale advective processes in the water column affected sediment conditions and removed surface macrofauna, influencing the slope and intercept of the regression models. In the outer fjord, lateral advection and subsequent sedimentation of terrestrial OM contributed a significant fraction to total OM sediments (〈14.76%). Stable carbon isotopes measured in benthic organisms suggest that benthic communities in the inner fjord may assimilate a significant fraction of terrestrial OM via heterotrophic bacteria in contrast to the minor input of terrestrial OM in the outer fjord.

Description: The Filchner-Rønne Outflow System (FROS) in the southernmost Weddell Sea is unique, as sea ice persists longer there than in any other region in the Southern Ocean (SO), strongly determining the ecological processes in the water column and on the seabed. It consists of the deep Filchner Trough (〉 1000 m in depth), which conducts water into and from the Filchner-Rønne Ice Shelf and separates two high-Antarctic shelf regions east and west of it. As the system is situated in a remote high-latitude area rather difficult to access, which greatly hampers scientific studies in the region, the knowledge about ecological processes in the FROS was scarce. However, during two cruises of R/V Polarstern in 2013/14 and 2015/16 field campaigns were performed, which united a multidisciplinary community of scientists intensely collaborating with a common overarching approach to study the FROS. Novel data was gathered by means of corers (multi-corer and multi-grab) and seabed imagery to investigate both infaunal and epifaunal seabed assemblages. First analyses indicated that the macro- and megabenthos on the shelf west of the Filchner Trough was clearly poorer in both abundance and diversity than that at eastern stations. Based on this evidence, we hypothesize that the western and eastern Filchner shelf regions are contrasting ecological systems, characterized by pronouncedly different environmental conditions and distinct benthic communities. We hypothesize further that this difference is primarily due to the contrasting sea-ice regimes, with almost permanent ice cover in the western region vs. the formation of a recurrent summer polynya in the east. As a result, the western system lacks the typical high-Antarctic summer conditions, such as occurrence of wide open-water areas, enhanced light regime, upper water-column stratification triggering phytoplankton blooms, high primary production and particle fluxes, and, hence, strong pelagic-benthic coupling and enhanced food supply to the benthos. In addition, this east-west contrast in the general environmental setting is sustained by the isolating effect of the regional oceanographic current pattern, impeding advective exchange processes (organic matter, larvae, propagules) between the two shelf regions across the trough. As there was evidence from bathymetric as well as seabed imaging data that iceberg scouring likewise impacts both the eastern and western shelf, we further hypothesize that this process, which is generally of high ecological significance for SO shelf benthic systems, does not explain the striking difference in epibenthic community structures. However, as the available evidence is based on admittedly rather few point-type and snapshot-like data, further samples are required to rigorously test those hypotheses.

Description: Glass sponges (Porifera, Hexactinellida) are important structuring components of the benthos in Antarctic shelf regions. These sessile filter feeders 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, we collected photos and videos of the ocean floor by using different gear equipped with HD cameras: a multi grab (MG), an Ocean Floor Observation System (OFOS) and a Remotely Operated Vehicle (ROV). For each of 28 stations, 30 images are selected and analyzed for abundance and species composition of glass sponges and their predators, as well as substrate characteristics. In addition to that, we measured temperature, salinity, dissolved silicate, particulate silicate and bacterial cell numbers. Furthermore, model and/or satellite data on current strength and mean annual ice cover will be included in the study. Glass sponge abundance will be analyzed 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.