Size,age and diet of polar cod,Boreogadus saida (Lepechin 1773), in ice covered waters

Summary Polar cod (Boreogadus saida) associated with drifting sea-ice were collected in the western Barents sea and north of Svalbard with dip-nets while SCUBA-diving in 1986 and 1987. Length-frequency measurements and otolith-readings suggested that the specimens were either one or two years old. The diet of fish from the western Barents sea (first-year ice) consisted mainly of copepods (Calanus finmarchicus, Calanus glacialis) and the hyperiid amphipod Parathemisto libellula. Fish collected north of the Svalbard archipelago (multi-year ice) had a more diverse diet, in which P. libellula and the sympagic amphipod Apherusa glacialis contributed more to the total diet biomass than copepods.     

Seasonal changes in zooplankton composition in the Barents Sea, with special attention to Calanus spp. (Copepoda)

The Barents Sea is an important area with respect to fisheriesresources (i.e. capelin and cod). In May, June and August 1981zooplankton biomass was measured along a transect at 30°E,from the ice border southwards. A maximum was recorded in Atlanticwater by the end of June (>100 g wet weight m^–2 InAugust the biomass values were relatively low south of the Polarfront and increased northwards into Arctic water (–50g m^–2 The species composition was influenced by the distributionof cold Arctic water and warmer Atlantic water. The zooplanktonwas dominated by the copepods Calanus finmarchicus and C. glacialis;the former is regarded as an Atlantic species and C. glacialisas an Arctic species.     

Mesozooplankton community structure and grazing impact in the Polar Frontal Zone of the south Indian Ocean during austral autumn 2002

Mesozooplankton community structure and grazing impact were investigated at 13 stations in the Polar Frontal Zone during the second Marion Offshore Variability Ecosystem Study (MOVES II), conducted during April 2002. Total integrated chl- a biomass ranged between 11.17 and 28.34 mg chl- a m^-2 and was always dominated by nano- and picophytoplankton (<20 µm). Throughout the study, small copepods, mainly Oithona similis and Ctenocalanus vanus, numerically dominated the mesozooplankton community, composing up to 85% (range 30-85%) of the total abundance. Grazing activity of the four most abundant copepods ( O. similis, C. vanus, Calanus simillimus and Clausocalanus spp.), constituting up to 93% of total mesozooplankton abundance, was investigated using the gut fluorescence technique. Results of gut fluorescence analyses indicated that Calanus simillimus and Clausocalanus spp. exhibited diel variability in gut pigments with maximum values recorded at night. In contrast, O. similis and Ctenocalanus vanus did not demonstrate diel variation in gut pigment contents. Ingestion rates of the four copepods ranged from 23.23 to 1462,02 ng(pigm.)ind^-1day^-1. The combined grazing impact of the four copepods ranged between 1 and 36% of the phytoplankton standing stock per day, with the highest daily impact occurring at stations occupied in the vicinity of the Antarctic Polar Front (~35.86% at station 23). Among the copepods, O. similis and Ctenocalanus vanus represented the most important consumers of phytoplankton biomass, collectively responsible for up to 89% (range 15-89%) of the total daily grazing impact. Carbon specific ingestion rates of the copepods varied between 42 and 320% body carbon per day.     

Zooplankton boom and ice amphipod bust below melting sea ice in the Amundsen Gulf, Arctic Canada

Early summer in the Arctic with extensive ice melt and break-up represents a dramatic change for sympagic–pelagic fauna below seasonal sea ice. As part of the International Polar Year-Circumpolar Flaw Lead system study (IPY-CFL), this investigation quantified zooplankton in the meltwater layer below landfast ice and remaining ice fauna below melting ice during June (2008) in Franklin Bay and Darnley Bay, Amundsen Gulf, Canada. The ice was in a state of advanced melt, with fully developed melt ponds. Intense melting resulted in a 0.3- to 0.5-m-thick meltwater layer below the ice, with a strong halocline to the Arctic water below. Zooplankton under the ice, in and below the meltwater layer, was sampled by SCUBA divers. Dense concentrations (max. 1,400 ind. m⁻³) of Calanus glacialis were associated with the meltwater layer, with dominant copepodid stages CIV and CV and high abundance of nauplii. Less abundant species included Pseudocalanus spp., Oithona similis and C. hyperboreus. The copepods were likely feeding on phytoplankton (0.5–2.3 mg Chl-a m⁻³) in the meltwater layer. Ice amphipods were present at low abundance (<10 ind. m⁻²) and wet biomass (<0.2 g m⁻²). Onisimus glacialis and Apherusa glacialis made up 64 and 51% of the total ice faunal abundance in Darnley Bay and Franklin Bay, respectively. During early summer, the autochthonous ice fauna becomes gradually replaced by allochthonous zooplankton, with an abundance boom near the meltwater layer. The ice amphipod bust occurs during late stages of melting and break-up, when their sympagic habitat is diminished then lost.     

Increased intrusion of warming Atlantic water leads to rapid expansion of temperate phytoplankton in the Arctic

The Arctic Ocean and its surrounding shelf seas are warming much faster than the global average, which potentially opens up new distribution areas for temperate‐origin marine phytoplankton. Using over three decades of continuous satellite observations, we show that increased inflow and temperature of Atlantic waters in the Barents Sea resulted in a striking poleward shift in the distribution of blooms of Emiliania huxleyi, a marine calcifying phytoplankton species. This species' blooms are typically associated with temperate waters and have expanded north to 76°N, five degrees further north of its first bloom occurrence in 1989. E. huxleyi's blooms keep pace with the changing climate of the Barents Sea, namely ocean warming and shifts in the position of the Polar Front, resulting in an exceptionally rapid range shift compared to what is generally detected in the marine realm. We propose that as the Eurasian Basin of the Arctic Ocean further atlantifies and ocean temperatures continue to rise, E. huxleyi and other temperate‐origin phytoplankton could well become resident bloom formers in the Arctic Ocean.     

Size-fractionated Primary Production in the South Atlantic and Atlantic Sectors of the Southern Ocean

Results are presented from size fractionated chlorophyll a (Chla) and primary production studies along a transect between Antarcticaand southern Africa during the second South African AntarcticMarine Ecosystem Study (SAAMES II), conducted in late australsummer (January to February) 1993. Total integrated Chl a alongthe transect was highest in the vicinity of the Marginal IceZone (MIZ) and Antarctic Polar Front (APF). At these stations,integrated Chl a biomass was always >25 mg Chl a m^–2and was dominated by microphytoplankton. Although nominal increasesinChl a biomass were also associated with the Subantarctic Front(SAF) and Subtropical Convergence (STC), total Chl a biomassin these regions was dominated by nanophytoplankton. Withinthe inter-frontal regions, total integrated Chl a biomass waslower, generally <25 mg Chl a m^–2, and was always dominatedby nanophytoplankton. An exception was found in the AgulhasReturn Current (ARC) where picophytoplankton dominated. Totaldaily integrated production along the transect ranged between60 and 436 mg C m^–2 day^–1. Elevated production rateswere recorded at stations occupied in the vicinity of the MIZand at all the major oceanic frontal systems. The contributionsof the various size fractions to total daily production displayedthe same spatial pattern as integrated biomass, with microphytoplanktonbeing the most important contributor in areas characterizedby elevated phytoplankton biomass. Outside these regions, nanophytoplanktondominated the total phytoplankton production. Again, an exceptionwas found in the ARC north of the STC where picophytoplanktondominated total production. There, the lowest production alongthe entire transect was recorded, with total daily integratedproduction always <90 mg C m^–2 day^–1. The increasedproduction rates recorded in the MIZ appeared to result fromincreased water column stability as indicated by a shallow mixed-layerdepth. Within the inter-frontal regions, the existence of adeep mixed layer appeared to limit phytoplankton production.Low silicate concentrations in the waters north of the APF mayalso have limited the growth of large microphytoplankton.     

Biogeographic structure of the microphytoplankton assemblages of the south Atlantic and Southern Ocean during austral summer

Microphytoplankton distribution in the Atlantic sector of theSouthern Ocean was investigated along a transect during theSAAMES II cruise undertaken in late austral summer (January/February) 1993. Samples were collected at 60 km intervals between34 and 70°S for the analysis of mineral nutrients, and theidentification and enumeration of microphytoplankton. Peaksin microphytoplankton abundance were recorded in the neriticwaters of Africa and Antarctica, at all major oceanic fronts,and in the marginal ice zone (MIZ). Partial correlation analysisindicated that 45% of the total variance associated with microphytoplanktonabundance could be explained by silicate and phosphate concentrations,while temperature accounted for 65% (P<0.001). Cluster andordination analyses identified two major groups of stations,one north and one south of the Subantarctic Front (SAF). Thisdivision appears to be related to differences in temperatureand silicate concentrations. Each region comprised distinctmicrophytoplankton subgroups associated with specific watermasses or hydrological features. Indicator species could beidentified for some water masses. In the MIZ, microphytoplanktonspecies composition and succession were strongly affected bysea-ice throughout the summer.     

Pigment distribution in the Pacific region of the Southern Ocean (autumn 1995)

Phytoplankton distribution patterns are still largely unknown for the Pacific region of the Southern Ocean. Pigment distributions were determined by HPLC on 40-m samples collected from the mixed layer during the ANTXII/4 cruise in March–May 1995 aboard RV “Polarstern”. A transect was covered (90°W, from 51°S to 70°S), crossing the Subantarctic Front in the north, the Polar Front, and the Southern Polar Front in the south. Coinciding with high concentrations of silicate, diatoms dominated in the Antarctic waters south of the Polar Front. North of the Polar Front, silicate concentrations dropped to values less than 10 μM. In this area flagellates (Prymnesiophyceae and green algae) were the dominant phytoplankton group. Nutrient depletion of the surface waters near the Southern Polar Front indicated formerly enhanced productivity. These findings confirmed previous observations by the British Sterna expedition, which described locally elevated chlorophyll a biomass near the southern boundary of the Southern Polar Front. We propose a role for supply of bioavailable iron via the front, and emphasise the importance of frontal systems for phytoplankton productivity in the Southern Ocean. Received: 11 June 1997 / Accepted: 16 November 1997     

Composition and community structure of pelagic copepods in the Indian sector of the Antarctic Ocean during the end of the austral summer

The present paper describes latitudinal and vertical changes in the composition, abundance and diversity of copepods in the Indian sector of the Antarctic Ocean, during the end of austral summer along a transect on 66°30′E between 43 and 62°S, within three layers (600–0, 200–0, 100–0 m). Highest copepod densities were noted in the central part of the transect, between the Antarctic Divergence and the Antarctic Convergence, with a maximum in the Antarctic Divergence zone, particularly in the upper levels of the water column. A total number of 80 copepod species were identified over the entire survey area. The south end and the central part of the transect comprised a small number of species. North of the Antarctic Convergence, this number increased markedly with the progressive disappearence of those species characteristic of Antarctic waters and their replacement by temperate and subtropical species. Generally, small copepods, particularly Oithona similis, Oithona frigida and Ctenocalanus citer, dominated in numbers in both Antarctic and sub-Antarctic areas. The contribution of large species to total copepod numbers was much lower, with Calanus simillimus in the central part of the transect, Pleuromamma borealis in the subtropical zone and Calanus propinquus in the southern part. Correspondence analysis showed a marked latitudinal gradient in population structure with four groups of samples and species corresponding to four latitudinal zones. Community structure (species richness, relative dominance index, evenness, Shannon species diversity index) and species abundance patterns (as rank-frequency diagrams) suggested that the maturity and species richness increased gradually from south to north. A low diversity index and evenness were observed in the area of the Antarctic Divergence, whereas the convergence zone showed high diversity and evenness. Conversely, the frontal zone showed high diversity and evenness. Distribution appeared unrelated to chlorophyll concentrations and on the large scale was related to the hydrologic characteristics. Received: 8 May 1996 / Accepted: 27 August 1996     

Movement of oceanic fronts south of Australia during the last 10 ka: interpretation of calcareous nannoplankton in surface sediments from the Southern Ocean

Preservation of calcareous nannoplankton in surface sediment samples from the Southern Ocean south of Australia and adjacent to New Zealand record a single assemblage. The dominant species are Emiliania huxleyi, Gephyrocapsa muellerae, Calcidiscus leptoporus, Helicosphaera carteri and Coccolithus pelagicus. The assemblage varies little in abundance and diversity with minor correlation to present-day overlying surface water masses and oceanic fronts. Increase in abundance of H. carteri and C. pelagicus in the region of the Subtropical Front may reflect higher nutrients associated with this front. The assemblage, although altered by dissolution, represents a warmer climatic interval than present-day with the presence of preferentially dissolved, warm-water species preserved as far south as the Polar Front. The presence of warm-water species under sub-Antarctic waters at the Polar Front is interpreted as a relic population from the Holocene climatic optimum of 10–8 ka. The absence of coccoliths in sediments poleward of the Polar Front suggests an equatorward shift of this front following the climatic optimum, resulting in increased productivity of siliceous phytoplankton associated with the colder waters and increased dissolution of coccoliths. Movement of the Subtropical Front for the same interval is not recorded in the preserved coccoliths. The more heavily calcified form of E. huxleyi which dominates the living assemblage north of the Subtropical Front is subject to dissolution in this region and is poorly preserved in the sediment assemblage.     

Zonal distribution and seasonal vertical migration of copepod assemblages in the Scotia Sea

Large, biomass-dominant Southern Ocean copepod species have been much studied, but small and mesopelagic species also play major rôles in these ecosystems. However, little is known of some basic aspects of their ecology. To address this, the abundances of 23 copepod species and genera were analysed from 72 stations sampled during the Discovery Expeditions in the 1920s to 1950s. Stratified net samples, usually to a depth of 1000?m, provided year-round coverage in the Scotia Sea from the Subantarctic Front to the Weddell-Scotia Confluence. Small copepods (Microcalanus pygmaeus, Ctenocalanus spp., Oncaea spp. and Oithona spp.) formed ～75% of total copepod abundance in the top 1000?m across all major zones. Oithona spp. composed ～40% of copepod numbers in the Polar Front area and to its south: further north their importance declined. All mesopelagic taxa except for the warmer-water species Metridia lucens and Pleuromamma robusta, extended throughout the entire study area, with smaller regional differences than for the shallower-living species. The species showed a continuum of temperature ranges, and there was no evidence that the Polar Front was a major biogeographic boundary to their distribution. Indeed, several important species, including Oithona spp. (mainly Oithona similis), Ctenocalanus spp., Metridia lucens and Rhincalanus gigas reached maximum numbers in this area. Total copepod abundance was thus higher in the vicinity of the Polar Front than in any other region. Only two copepod families made pronounced seasonal vertical migrations: Eucalaniidae (Eucalanus longiceps and R. gigas) and Calaniidae (Neocalanus tonsus, Calanoides acutus, Calanus simillimus and Calanus propinquus). Some evidence for a winter descent was found for Ctenocalanus spp. and some deeper-living groups: Euchaeta spp. and the Metridiidae, although their migrations were not so great as for the eucalanids and calanids.     

Protist community composition in the Pacific sector of the Southern Ocean during austral summer 2010

Knowledge about the protist diversity of the Pacific sector of the Southern Ocean is scarce. We tested the hypothesis that distinct protist community assemblages characterize large-scale water masses. Therefore, we determined the composition and biogeography of late summer protist assemblages along a transect from the coast of New Zealand to the eastern Ross Sea. We used state of the art molecular approaches, such as automated ribosomal intergenic spacer analysis and 454-pyrosequencing, combined with high-performance liquid chromatography pigment analysis to study the protist assemblage. We found distinct biogeographic patterns defined by the environmental conditions in the particular region. Different water masses harbored different microbial communities. In contrast to the Arctic Ocean, picoeukaryotes had minor importance throughout the investigated transect and showed very low contribution south of the Polar Front. Dinoflagellates, Syndiniales, and small stramenopiles were dominating the sequence assemblage in the Subantarctic Zone, whereas the relative abundance of diatoms increased southwards, in the Polar Frontal Zone and Antarctic Zone. South of the Polar Front, most sequences belonged to haptophytes. This study delivers a comprehensive and taxon detailed overview of the protist composition in the investigated area during the austral summer 2010.     

Breaking the ice: large-scale distribution of mesozooplankton after a decade of Arctic and transpolar cruises

Mesozooplankton collected during five summer expeditions to the Arctic Ocean between 1987 and 1991 was analysed for regional patterns in biomass and species distribution, distinguishing between an epipelagic (0–100 m) and a deeper (0–500 m) layer. A total of 58 stations was sampled mainly in the Nansen, Amundsen and Makarov Basins of the central Arctic Ocean and in areas of the Greenland Sea, West Spitsbergen Current and Barents Sea. Results from the different expeditions were combined to create a transect extending from the Fram Strait across the Eurasian Basin into the Makarov Basin. Mesozooplankton dry mass in the upper 500 m decreased from 8.4 g m⁻² in the West Spitsbergen Current to less than 2 g m⁻² in the high-Arctic deep-sea basins. In the central Arctic Ocean, biomass was concentrated in the upper 100 m and was dominated by the large copepods Calanus hyperboreus and C. glacialis. In contrast, the mesozooplankton in the West Spitsbergen Current was more evenly distributed throughout the upper 500 m, with C. finmarchicus as the prevailing species. The distribution of abundant mesopelagic species reflected the hydrographic regime: the calanoid copepod Gaetanus tenuispinus and the hyperiid amphipod Themisto abyssorum were most abundant in the Atlantic inflow, while Scaphocalanus magnus was a typical component of the high-Arctic fauna. The relatively high mesozooplankton biomass and the occurrence of boreal-Atlantic species in the central Arctic Ocean are indicators for the import of organic material from allochthonous sources, especially from the northern North Atlantic. Hence, in spite of its enclosure by land masses, the Arctic Ocean is characterized by an exchange of water masses and organisms with the North Atlantic, and advection processes strongly influence the distribution of plankton species in this high-latitude ecosystem. Received: 18 December 1997 / Accepted: 11 April 1998     

Regional and temporal variation of Oithona spp. biomass, stage structure and productivity in the Irminger Sea, North Atlantic

Oithona spp. standing stock and production is considered relativelystable in space and time as a result of continuous breeding,low metabolism, reduced predation mortality and the abilityof these small cyclopoids to exploit microbial food webs moreefficiently than larger copepods. However, through a reviewof the published literature, we show that Oithona spp. biomasscan vary widely both over the year and with latitude. Thus,the present study set out to investigate the basin scale variabilityin biomass, stage structure and reproduction of Oithona spp.in relation to changes in hydrographic, physico-chemical andbiological parameters encountered during three cruises conductedbetween April and November 2002 in the Irminger Sea, North Atlantic.Here we found that Oithona spp. biomass varied significantlywith temperature and with dinoflagellates biomass concentration.On the other hand, Oithona similis egg production rates increasedwith both ciliates and dinoflagellates concentrations, ratherthan with temperature. The inverse relationship we found betweenOithona spp. naupliar recruitment with Calanus spp. and fishlarvae abundance suggests that predation pressure may contributeto control the spatial variation in the stage structure andbiomass of Oithona spp. and that the nauplii of this genus mayserve as a food source for other planktonic organisms priorto the spring phytoplankton bloom.     

Ice algal assemblages and vertical export of organic matter from sea ice in the Barents Sea and Nansen Basin (Arctic Ocean)

Algal communities and export of organic matter from sea ice were studied in the offshore marginal ice zone (MIZ) of the northern Barents Sea and Nansen Basin of the Arctic Ocean north of Svalbard by means of ice cores and short-term deployed sediment traps. The observations cover a total of ten stations within the drifting pack ice, visited over a period of 3 years during the period of ice melt in May and July. Maximum flux of particulate organic carbon and chlorophyll a from the ice at 1 m depth (1,537 mg C m⁻² per day and 20 mg Chl a m⁻² per day) exceeded the flux at 30 m by a factor of 2 during spring, a pattern that was reversed later in the season. Although diatoms dominated the ice-associated algal biomass, flagellates at times revealed similarly high biomass and typically dominated the exported algal carbon. Importance of flagellates to the vertical flux increased as melting progressed, whereas diatoms made the highest contribution during the early melting stage. High export of ice-derived organic matter and phytoplankton took place simultaneously in the offshore MIZ, likely as a consequence of ice drift dynamics and the mosaic structure of ice-covered and open water characteristic of this region.     

Plankton dynamics in the marginal ice zone of the central Barents Sea during spring: carbon flow and structure of the grazer food chain

Plankton community structure was analysed during spring at four stations along a transect from the polar ice into open waters of the Barents Sea. The transect mimicks a time span of months in the biological succession during the Arctic summer. The significance of the microbial food web vs the more classical food web was evaluated using carbon budget models. The standing stocks of diatom-dominated phytoplankton and bacteria were generally high especially in connection to ice. The biomass of microzooplankton, dominated by heterotrophic dinoflagellates was significantly high, with specific growth rates following the in situ temperature. The mean ± SE specific growth rate was 0.40±0.12 d^?1 for ciliates and 0.24 ± 0.05 d^?1 for heterotrophic dinoflagellates, indicating no food limitation. The estimated total carbon requirement for microzooplankton was, at the ice-covered station, approximately 100% of the daily primary production, decreasing to 25% in the open water. Carbon-specific secondary production of the copepodsCalanus finmarchicus (Gunnerus),C. glacialis (Jaschnov),C. hyperboreus (Krøyer) andMetridia longa (Lubbock) were analysed by egg production.C. finmarchicus andM. longa were productive at all stations, including the ice-covered locations, with a maximum at 0.08 d^?1 and 0.035 d^?1, respectively. The other, more Arctic-related,Calanus spp. were virtually outspawned. The standing stock of copepods was only 10–20% of the total microbial grazer biomass. The community growth and grazing by copepods showed significantly less quantitative importance for the pelagic carbon flow than the microbial processes.     

Phytoplankton composition in the Weddell-Scotia Confluence area during austral spring in relation to hydrography

During the EPOS leg 2 cruise of the RV Polarstern, carried out in late austral spring of 1988–1989, the composition of phytoplankton in relation to the distribution of hydrographic parameters was studied in four successive transects carried out along 49°W and 47°W, across the Weddell-Scotia Confluence (WSC) and the marginal ice zone (which overlapped in part). In all transects, a maximum of phytoplankton biomass was found in the WSC, in surface waters stabilized by ice melting. Different phytoplankton assemblages could be distinguished. North of the Scotia Front (the northern limit of the WSC) diatoms with Chaetoceros neglectus, Nitzschia spp. and (Thalassiosira gravida) dominated the phytoplankton community. This assemblage appeared to have seeded a biomass maximum which occupied, during the first transect, an area of the WSC, south of the Scotia Front. The southernmost stations of the first transect and all the stations to the south of the Scotia Front in the other transects were populated by a flagellate assemblage (with a cryptomonad, Pyramimonas spp. and Phaeocystis sp.) and an assemblage of diatoms (Corethron criophilum and Tropidoneis vanheurkii among others) associated to the presence of ice. During the last three transects, the flagellate assemblage formed a bloom in the low salinity surface layers of the WSC zone. The bulk of the biomass maximum was formed by the cryptomonad which reached concentrations up to 4×10⁶ cells l^–1 towards the end of the cruise. Multivariate analysis is used to summarize phytoplankton composition variation. The relationships between the distribution of the different assemblages and the hydrographic conditions indicate that the change of dominance from diatoms to flagellates in the WSC zone was related to the presence of water masses from different origin.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Impact of warm water advection on the winter zooplankton community in an Arctic fjord

The west coast of Spitsbergen is influenced by water masses of Atlantic and Arctic origin. During the winter of January–April 2006, water temperatures on the West Spitsbergen Shelf were ∼3°C warmer than typical winter conditions, leading to a coastal sea ice cover of reduced thickness, extent and duration. A sediment trap deployed from September 2005 to May 2006 in the outer basin of Kongsfjorden (NW Spitsbergen) at a depth of 115 m has provided a continuous winter time-series of zooplankton during a period of rapid increase in water temperatures. Prior to an anomalous and prolonged influx of warm Atlantic water (AW) starting at the end of January, the trap samples were dominated by the boreo-Arctic copepod Metridia longa. Species that increased in abundance during the influx included late stages of Calanus finmarchicus, C. glacialis, C. hyperboreus and Paraeuchaeta norvegica. The early introduction of shelf populations into the fjord, and thus increased copepod biomass relative to typical winter conditions with little advection, has implications for the marine pelagic food web and pelagic-benthic coupling.     

Phytoplankton dynamics in relation to hydrography, nutrients and zooplankton at the onset of sea ice formation in the eastern Weddell Sea (Antarctica)

The quantitative and qualitative distribution of phytoplankton was investigated along five North–South transects in the eastern Weddell Sea during the transition from late autumn to winter. Relationships with the regional hydrography, progressing sea ice coverage, nutrient distribution and zooplankton are discussed and compared with data from other seasons. To the north of the Antarctic Slope Front (ASF) a remnant temperature minimum layer was found above the primary pycnocline throughout summer. Surface waters had not entirely acquired typical winter characteristics. While temperature was already in the winter range, this was not the case for salinity. Highest biomass of phytoplankton, with the exception of the first transect, was found in the region adjoining the ASF to the north. Absolute chlorophyll a (Chl a) concentrations dropped from 0.35 to 0.19 g l^–1 . Nutrient pools exhibited a replenishing tendency. Ammonium concentrations were high (0.75–2 mol l^–1), indicating extensive heterotrophic activity. The phytoplankton in the ASF region was dominated by nanoflagellates, particularly Phaeocystis spp.. North of the ASF the abundance of diatoms increased, with Fragilariopsis spp., F. cylindrus and Thalassiosira spp. dominating. Community structure varied both due to hydrographical conditions and the advancing ice edge. The phytoplankton assemblage formed during late autumn were very similar to the ones found in early spring. A POC/PON ratio close to Redfield, decreasing POC concentration and a high phaeophytin/Chl a ratio, as well as a high abundance of mesozooplankton indicated that a strong grazing pressure was exerted on the phytoplankton community. A comparison between primary production (PP) in the water column and the sea ice showed a shift of the major portion of PP into the ice during the period of investigation.     

A major feeding ground for cetaceans and seabirds in the south-western Greenland Sea

In the frame of our long-term study of the distribution of seabirds and marine mammals in polar seas, observers from this team participated in the European Arctic expeditions of icebreaking RV Polarstern during summer 2008. The main aims were to obtain more information on the mechanisms underlying the at-sea distribution of the ??higher trophic levels?? and to detect possible temporal and spatial changes in numbers, especially in function of climatic changes and decreasing ice coverage in the Arctic. In total, 1,175 half-an-hour transect counts were devoted to seabird and marine mammal distribution in the Greenland and Norwegian Seas, from 14 June to 15 August, 2008. A major feeding ground for cetaceans and seabirds was detected in the south-western Greenland Sea and the Denmark Strait in the Polar Front between Polar and Arctic Water masses. For the main cetacean and seabird species, almost all individuals recorded during the whole expedition were encountered in this limited zone of 33 counts: 135 humpback whales Megaptera novaeangliae and 1,940 common guillemots Uria aalge. Moreover, 4,400 fulmars Fulmarus glacialis light morph were observed in this zone, i.e. close to half of the total. All were actively feeding, making this zone the major feeding ground for the higher trophic levels in the European Arctic Seas and so confirming the great importance of fronts (upwellings) for the biological productivity of the oceans. Such data are essential for a successful conservation and management of the Denmark Strait and adjacent areas.