(Table 1) Sympagic meiofauna and amphipods inhabiting the meltponds in the Central Arctic sampled during POLARSTERN cruise ARK-XXII/2

Meltponds on Arctic sea ice have previously been reported to be devoid of marine metazoans due to fresh-water conditions. The predominantly dark frequently also green and brownish meltponds observed in the Central Arctic in summer 2007 hinted to brackish conditions and considerable amounts of algae, possibly making the habitat suitable for marine metazoans. Environmental conditions in meltponds as well as sympagic meiofauna in new ice covering pond surfaces and in rotten ice on the bottom of ponds were studied, applying modified techniques from sea-ice and under-ice research. Due to the very porous structure of the rotten ice, the meltponds were usually brackish to saline, providing living conditions very similar to sub-ice water. The new ice cover on the surface had similar characteristics as the bottom layer of level ice. The ponds were thus accessible to and inhabitable by metazoans. The new ice cover and the rotten ice were inhabited by various sympagic meiofauna taxa, predominantly ciliates, rotifers, acoels, nematodes and foraminiferans. Also, sympagic amphipods were found on the bottom of meltponds. We suggest that, in consequence of global warming, brackish and saline meltponds are becoming more frequent in the Arctic, providing a new habitat to marine metazoans.

Stable carbon isotope composition of benthic foraminifera from sediments of the Skagerrak, North Sea

The sediment cores 225514 and 225510 were recovered from 420 and 285 m water depth, respectively. They were investigated for their benthic foraminiferal delta13C during the last 500 years. Both cores were recovered from the southern flank of the Skagerrak. The delta13C values of Uvigerina mediterranea and other shallow infaunal species in both cores indicate that organic matter rain rates to the seafloor varied around a mean value until approximately AD 1950 after which they increased. This increase might result from changes in the North Atlantic Current System and a co-occurring persistently high North Atlantic Oscillation index state in the 1980s to 1990s, rather than from anthropogenic eutrophication. Using delta13C mean values of multiple species, we reconstruct delta13C gradients of dissolved inorganic carbon (DIC) within pore waters for the time periods AD 1500 to 1950 and AD 1950 to 2000. The calculated delta13CDIC ranges, interpreted as indicating total organic matter remineralization due to respiration, are generally bigger in Core 225514 than in Core 225510. Since mean delta13C values of U. mediterranea suggest that organic matter rain rates were similar at both locations, differences in total organic matter remineralization are attributed to differing oxygen availability. However, oxygen concentrations in the overlying bottom water masses are not likely to have differed significantly. Thus, we suggest that organic matter remineralization was controlled by oxygen availability within the sediments, reflecting strong differences in sedimentation rates at the two investigated core sites. Based on the assumptions that tests of benthic foraminiferal species inhabiting the same microhabitat depth should show equal delta13C values unless they are affected by vital effects and that Globobulimina turgida records pore water delta13CDIC, we estimate microhabitat-corrected vital effects for several species with respect to G. turgida: >0.7 per mil for Cassidulina laevigata, >1.3 per mil for Hyalinea balthica, and >0.7 per mil for Melonis barleeanus. Melonis zaandami seems to closely record pore water delta13CDIC.

Geo-referenced photo-mosaics of the Menez Gwen Hydrothermal Vent (Mid-Atlantic Ridge)

The Menez Gwen hydrothermal vents, located on the flanks of a small young volcanic structure in the axial valley of the Menez Gwen seamount, are the shallowest known vent systems on the Mid-Atlantic Ridge that host chemosynthetic communities. Although visited several times by research cruises, very few images have been published of the active sites, and their spatial dimensions and morphologies remain difficult to comprehend. We visited the vents on the eastern flank of the small Menez Gwen volcano during cruises with RV Poseidon (POS402, 2010) and RV Meteor (M82/3, 2010), and used new bathymetry and imagery data to provide first detailed information on the extents, surface morphologies, spatial patterns of the hydrothermal discharge and the distribution of dominant megafauna of five active sites. The investigated sites were mostly covered by soft sediments and abundant white precipitates, and bordered by basaltic pillows. The hydrothermally-influenced areas of the sites ranged from 59 to 200 m**2. Geo-referenced photomosaics and video data revealed that the symbiotic mussel Bathymodiolus azoricus was the dominant species and present at all sites. Using literature data on average body sizes and biomasses of Menez Gwen B. azoricus, we estimated that the B. azoricus populations inhabiting the eastern flank sites of the small volcano range between 28,640 and 50,120 individuals with a total biomass of 50 to 380 kg wet weight. Based on modeled rates of chemical consumption by the symbionts, the annual methane and sulfide consumption by B. azoricus could reach 1760 mol CH4 yr**-1 and 11,060 mol H2S yr**-1. We propose that the chemical consumption by B. azoricus over at the Menez Gwen sites is low compared to the natural release of methane and sulfide via venting fluids.

Chlorophyll a content, protist biomass and experimental plankton growth and mortality in West Greenland water samples

We evaluated the role of microzooplankton (sensu latto, grazers <500 µm) in determining the fate of phytoplankton production (PP) along a glacier-to-open sea transect in the Greenland subarctic fjord, Godthabfjord. Based on the distribution of size fractionated chlorophyll a (chl a) concentrations we established 4 zones: (1) Fyllas Bank, characterized by deep chl a maxima (ca. 30 to 40 m) consisting of large cells, (2) the mouth and main branch of the fjord, where phytoplankton was relatively homogeneously distributed in the upper 30 m layer, (3) inner waters influenced by glacial melt water and upwelling, with high chl a concentrations (up to 12 µg/l) in the >10 µm fraction within a narrow (2 m) subsurface layer, and (4) the Kapisigdlit branch of the fjord, ice-free, and characterized with a thick and deep chl a maximum layer. Overall, microzooplankton grazing impact on primary production was variable and seldom significant in the Fyllas Bank and mouth of the fjord, quite intensive (up to >100% potential PP consumed daily) in the middle part of the main and Kapisigdlit branches of the fjord, and rather low and unable to control the fast growing phytoplankton population inhabiting the nutrient rich waters in the upwelling area in the vicinity of the glacier. Most of the grazing impact was on the <10 µm phytoplankton fraction, and the major grazers of the system seem to be >20 µm microzooplankton, as deducted from additional dilution experiments removing this size fraction. Overall, little or no export of phytoplankton out of the fjord to the Fyllas Bank can be determined from our data.

Fatty acids and intact polar lipids of laminated microbial sediments from St. Peter Ording, German Wadden Sea

Hidden for the untrained eye through a thin layer of sand, laminated microbial sediments occur in supratidal beaches along the North Sea coast. The inhabiting microbial communities organize themselves in response to vertical gradients of light, oxygen or sulfur compounds. We performed a fine-scale investigation on the vertical zonation of the microbial communities using a lipid biomarker approach, and assessed the biogeochemical processes using a combination of microsensor measurements and a 13C-labeling experiment. Lipid biomarker fingerprinting showed the overarching importance of cyanobacteria and diatoms in these systems, and heterocyst glycolipids revealed the presence of diazotrophic cyanobacteria even in 9 to 20 mm depth. High abundance of ornithine lipids (OL) throughout the system may derive from sulfate reducing bacteria, while a characteristic OL profile between 5 and 8 mm may indicate presence of purple non-sulfur bacteria. The fate of 13C-labeled bicarbonate was followed by experimentally investigating the uptake into microbial lipids, revealing an overarching importance of cyanobacteria for carbon fixation. However, in deeper layers, uptake into purple sulfur bacteria was evident, and a close microbial coupling could be shown by uptake of label into lipids of sulfate reducing bacteria in the deepest layer. Microsensor measurements in sediment cores collected at a later time point revealed the same general pattern as the biomarker analysis and the labeling experiments. Oxygen and pH-microsensor profiles showed active photosynthesis in the top layer. The sulfide that diffuses from deeper down and decreases just below the layer of active oxygenic photosynthesis indicates the presence of sulfur bacteria, like anoxygenic phototrophs that use sulfide instead of water for photosynthesis.

Fauna associated with Bathymodiolus azoricus mussel beds within hydrothermal fields of the Mid-Atlantic Ridge

Structure of assemblages associated with mussel aggregations of Bathymodiolus azoricus was investigated. Mussel beds were found on hydrothermal vent fields on the Mid-Atlantic Ridge (Menez Gwen, Lucky Strike, and Rainbow) at depths 850-2400 m. The community structure of the mussel bed assemblages varied between studied areas. Large number of species was unique to mussel beds of the Menez Gwen field; the most observed taxa were not specialized hydrothermal species. All other nonunique species were found within the Lucky Strike region. The lowest mussel assemblage structure evenness was observed in the shallowest Menez Gwen area (850 m depth). We assume that two types of mussel assemblages (nematode-dominated and copepod-dominated) exist within the Lucky Strike field. The assemblages of B. azoricus differ significantly from assemblages of B. thermophilus inhabiting Pacific hydrothermal vents.

Biomass of seston in the benthic layer of the Southwestern Indian Ocean

At stations to 1530 m depth in the Mozambique Channel and on the Saya-de-Malha and Walters banks seston biomass 2 m above the bottom was lower than at 30 m. Above the Walters shoal this difference was 13.2 mg/m**3 and was not equal to zero for P < 0.001. These results contradict previous ideas of biomass increase in benthic layers. The most likely cause of the observed impoverishment of plankton may be predominant consumption of living zooplankton component of seston by bottom and near-bottom predators. In the area of the Walters shoal this consumption is estimated as being about 300 mg/m**2 per day. Animals inhabiting this area live mainly on plankton brought in by horizontal advection, so that existence of faunal assemblages even on shallow-water submarine elevations is supported not mainly by local photosynthesis, but by primary production of surrounding waters.

(Table 2) Distribution of alkenone unsaturation index UK37 of the eastern North Atlantic

This paper reports the concentrations and within-class distributions of long-chain alkenones and alkyl alkenoates in the surface waters (0-50 m) of the eastern North Atlantic, and correlates their abundance and distribution with those of source organisms and with water temperature and other environmental variables. We collected these samples of >0.8 µm particulate material from the euphotic zone along the JGOFS 20°W longitude transect, from 61°N to 24°N, during seven cruises of the UK-JGOFS Biogeochemical Ocean Flux Study (BOFS) in 1989-1991; the biogeographical range of our 53 samples extends from the cold (<10°C), nutrient-rich and highly productive subarctic waters of the Iceland Basin to the warm (>25°C) oligotrophic subtropical waters off Africa. Surface water concentrations of total alkenone and alkenoates ranged from <50 ng/l in oligotrophic waters below 40°N to 2000-4500 ng/l in high latitude E. huxleyi blooms, and were well correlated with E. huxleyi cell densities, supporting the assumption that E. huxleyi is the predominant source of these compounds in the present day North Atlantic. The within-class distribution of the C37 and C38 alkenones and C36 alkenoates varied strongly as a function of temperature, and was largely unaffected by nutrient concentration, bloom status and other surface water properties. The biosynthetic response of the source organisms to growth temperature differed between the cold (<16°C) waters above 47°N and the warmer waters to the south. In cold (<16°C) waters above 47°N, the relative amounts of alkenoates and C38 alkenones synthesized was a strong function of growth temperature, while the unsaturation ratio of the alkenones (C37 and C38) was uncorrelated with temperature. Conversely, in warm (>16°C) waters below 47°N, the relative proportions of alkenoates and alkenones synthesized remained constant with increasing temperature while the unsaturation ratios of the C37 and C38 methyl alkenones (Uk37 and Uk38Me, respectively) increased linearly. The fitted regressions of Uk37 and Uk38Me versus temperature for waters >16°C were both highly significant (r**2 > 0.96) and had identical slopes (0.057) that were 50% higher than the slope (0.034) of the temperature calibration of Uk37 reported by Prahl and Wakeham (1987; doi:10.1038/330367a0) over the same temperature range. These observations suggest either a physiological adjustment in biochemical response to growth temperature above a 16-17°C threshold and/or variation between different E. huxleyi strains and/or related species inhabiting the cold and warm water regions of the eastern North Atlantic. Using our North Atlantic data set, we have produced multivariate temperature calibrations incorporating all major features of the alkenone and alkenoate data set. Predicted temperatures using multivariate calibrations are largely unbiased, with a standard error of approximately ±1°C over the entire data range. In contrast, simpler calibration models cannot adequately incorporate regional diversity and nonlinear trends with temperature. Our results indicate that calibrations based upon single variables, such as Uk37, can be strongly biased by unknown systematic errors arising from natural variability in the biosynthetic response of the source organisms to growth temperature. Multivariate temperature calibration can be expected to give more precise estimates of Integrated Production Temperatures (IPT) in the sedimentary record over a wider range of paleoenvironmental conditions, when derived using a calibration data set incorporating a similar range of natural variability in biosynthetic response.

Physiological and biochemical characteristics of Calanoides carinatus in waters off the coast of Namibia

Biochemical composition, feeding and oxygen uptake rate of mass planktic copepod Calanoides carinatus were studied off the coast of Namibia in January 1986. Population of this species in the area had two parts: the surface group inhabiting the 0-100 m layer and the deep part inhabiting depths greater than 200 m. Individuals in the surface and deep parts of the population differed in food content of guts, lipid content of bodies, oxygen uptake rate and behavior. Differences in biochemical composition and rate of physiological processes indicate that individuals in the deep part of the population are in diapause. Nature of changes in biochemical composition of C. carinatus in surface and deep waters in relation to life cycle characteristics in upwelling waters are discussed.

Abiotic characteristics and diatom abundance and biomass in different sectors of the Argentinien Shelf and antartic waters

A large spatial scale study of the diatom species inhabiting waters from the subantarctic (Argentine shelf) to antarctic was made for the first time in order to understand the relationships between these two regions with regard to the fluctuations in diatom abundances in relation with environmental features, their floristic associations and the effect of the Polar Front as a biogeographic barrier. Species-specific diatom abundance, nutrient and chlorophyll-a concentration were assessed from 64 subsurface oceanographic stations carried out during the austral summer 2002, a period characterized by an anomalous sea-ice coverage corresponding to a ''warm year". Significant relationships of both diatom density and biomass with chlorophyll-a (positive) and water temperature (negative) were found for the study area as a whole. Within the Subantarctic region, diatom density and biomass values were more uniform and significantly (in average: 35 and 11 times) lower than those of the Antarctic region, and did not correlate with chlorophyll-a. In antarctic waters, instead, biomass was directly related with chlorophyll-a, thus confirming the important contribution of diatoms to the Antarctic phytoplanktonic stock. A total of 167 taxa were recorded for the entire study area, with Chaetoceros and Thalassiosira being the best represented genera. Species richness was maximum in subantarctic waters (46; Argentine shelf) and minimum in the Antarctic region (21; Antarctic Peninsula), and showed a significant decrease with latitude. Floristic associations were examined both qualitatively (Jaccard Index) and quantitatively (correlation) by cluster analyses and results allowed differentiating a similar number of associations (12 vs. 13, respectively) and two main groups of stations. In the Drake Passage, the former revealed that the main floristic change was found at the Polar Front, while the latter reflected the Southern ACC Front as a main boundary, and yielded a higher number of isolated sites, most of them located next to different Antarctic islands. Such differences are attributed to the high relative density of Fragilariopsis kerguelensis in Argentine shelf and Drake Passage waters and of Porosira glacialis and species of Chaetoceros and Thalasiosira in the Weddell Sea and near the Antarctic Peninsula. From a total of 84 taxa recorded in antarctic waters, only 17 were found exclusively in this region, and the great majority (67) was also present in subantarctic waters but in extremely low (< 1 cell/l) concentrations, probably as a result of expatriation processes via the ACC-Malvinas Current system. The present results were compared with those of previous studies on the Antarctic region with respect to both diatom associations in regular vs. atypically warm years, and the distribution and abundance of some selected planktonic species reported for surface sediments.

Impacts of ocean warming and acidification on the larval development of the barnacle Amphibalanus improvisus

The world's oceans are warming and becoming more acidic. Both stressors, singly or in combination, impact marine species, and ensuing effects might be particularly serious for early life stages. To date most studies have focused on ocean acidification (OA) effects in fully marine environments, while little attention has been devoted to more variable coastal ecosystems, such as the Western Baltic Sea. Since natural spatial and temporal variability of environmental conditions such as salinity, temperature or pCO2 impose more complex stresses upon organisms inhabiting these habitats, species can be expected to be more tolerant to OA (or warming) than fully marine taxa. We present data on the variability of salinity, temperature and pH within the Kiel Fjord and on the responses of the barnacle Amphibalanus improvisus from this habitat to simulated warming and OA during its early development. Nauplii and cyprids were exposed to different temperature (12, 20 and 27°C) and pCO2 (nominally 400, 1250 and 3250 µatm) treatments for 8 and 4 weeks, respectively. Survival, larval duration and settlement success were monitored. Warming affected larval responses more strongly than OA. Increased temperatures favored survival and development of nauplii but decreased survival of cyprids. OA had no effect upon survival of nauplii but enhanced their development at low (12°C) and high (27°C) temperatures. In contrast, at the intermediate temperature (20°C), nauplii were not affected even by 3250 µatm pCO2. None of the treatments significantly affected settlement success of cyprids. These experiments show a remarkable tolerance of A. improvisus larvae to 1250 µatm pCO2, the level of OA predicted for the end of the century.