Mesozooplankton assemblages in the shallow Arctic Laptev Sea in summer 1993 and autumn 1995

Mesozooplankton distribution and composition in the very shallow part of the Siberian Laptev Sea shelf were studied during the German-Russian expeditions “Transdrift I” (August/September 1993) and “Transdrift III” (October 1995). Maximum abundances were found close to the outflow of the Lena River (7,965 ind. m⁻³) and in the Yana river mouth (38,163 ind. m⁻³). Lowest abundances occurred in the northeast and west of the Laptev Sea (64–95 ind. m⁻³). Highest biomass values (104–146 mg DM m⁻³) were determined in the northern and northeastern part of the shallow Laptev Sea, as well as close to the river outflows, with a record biomass maximum in the Yana river mouth (270 mg DM m⁻³). Biomass minima were situated north of the Lena Delta and in the western part of the shallow Laptev Sea (0.3–1.0 mg DM m⁻³). Copepods dominated in terms of abundance and biomass. Cluster analyses separated four mesozooplankton assemblages: the assemblage “Lena/Yana” in the southern part, “Eastern-central” in the centre, “Kotelnyy” in the eastern part and “Taimyr” in the western part of the shallow Laptev Sea. The small-sized neritic and brackish-water copepods Drepanopus bungei, Limnocalanus grimaldii and Pseudocalanus major occurred in enormous numbers and made up the bulk of zooplankton abundance and biomass in the very shallow part of the Laptev Sea close to the rivers Lena and Yana. In the more northern and northeastern areas, Calanus glacialis, P. minutus and P. major were dominant copepod species, whereas Oithona similis and Acartia sp. became important in the western Laptev Sea. Appendicularians, as well as hydromedusae and the chaetognath Sagitta sp., contributed significantly to abundance and biomass, respectively, but not over the entire area studied. One can identify taxon-specific distribution patterns (e.g. Sagitta predominated the biomass in a zone between the area heavily influenced by Lena/Yana and the offshore area to the north), which differ from the patterns revealed by cluster analysis. Hydrographic features, especially the enormous freshwater inflow, apparently determine the occurrence and formation of zooplankton aggregations. Extremely high numbers of small-sized neritic and brackish-water copepods occurred locally, which were probably also supported by excellent feeding conditions.     

Reproduction of Calanus glacialis in the Laptev Sea, Arctic Ocean

Abundance and reproductive biology (gonad maturation and egg production) of the Arctic copepod Calanus glacialis were studied in the Laptev Sea and adjacent Arctic Ocean in September 1993 and from July to September 1995. Both abundance and reproductive activity were subject to strong spatial and seasonal variability, which was related to the ice cover, feeding conditions and circulation pattern. Maximum abundance of the C. glacialis population was generally confined to the outer shelf and slope with depths between 50 and 1000 m. During both cruises, highest egg production rates and largest number of young copepodite stages were observed in the eastern Laptev Sea, where the development of the C. glacialis population seems to follow the opening of the “Siberian Polynya”. In the western part, which is usually covered by pack ice, females were all immature, and no young stages were found. However, females responded quickly to a temporary opening of the ice there in 1995 and spawned. Starvation experiments showed that food-independent reproduction fuelled by internal energy resources was at least partly responsible for relatively high egg production rates at low ambient food concentrations. Egg production rates in starved females were considerably higher than those previously reported. Accepted: 14 June 2000     

Distribution patterns of diatom surface sediment assemblages in the Laptev Sea (Arctic Ocean)

The modern diatom distribution in the Laptev Sea, Arctic Ocean, was investigated in 89 surface sediment samples. Diatom concentrations are relatively low showing values between 0.01×10⁶ and 6.7×10⁶ valves per gram dry sediment. Based on a factor analysis using seventeen taxa or taxa groups five diatom surface sediment assemblages can be defined: the ice diatom assemblage of the central region of the Laptev Sea, the Chaetoceros assemblage of the eastern and southeastern shelf, the Thalassiosira antarctica assemblage of the continental slope and deep sea, the freshwater diatom assemblage in the vicinity of river mouths and deltas, and the Thalassiosira nordenskioeldii assemblage which shows a patchy occurrence on the central Laptev Sea shelf. The distribution pattern of diatom assemblages in surface sediment is significantly related to oceanographic conditions of surface water masses. The main factors controlling the distribution of diatoms in the Laptev Sea are the riverine freshwater input during the summer which strongly affects the salinity conditions, and the sea-ice extent. Furthermore, the composition of the Thalassiosira antarctica assemblage of the continental slope is largely influenced by dissolution and lateral transport processes.     

Composition and distribution of zooplankton in the Laptev Sea and adjacent Nansen Basin during summer, 1993

Zooplankton composition and distribution were investigated on the Laptev Sea shelf, over the continental slope and in the adjacent deep Nansen Basin during the joint German-Russian expedition “Arctic 93” with RV Polarstern and Ivan Kireyev in August/September 1993. In the shelf area biomass decreased from west to east with the lowest values in the area influenced by the Lena river runoff. A gradual increase of biomass from the shallow to the deep area correlated with water depth. Total biomass ranged between 0.1 and 1.5 g m⁻² on the shelf and 4.7 and 7.9 g m⁻² in the adjacent Nansen Basin. On the shelf Calanus glacialis/finmarchicus dominated overall. The contribution of brackish-water taxa was low in the west, where high salinity and southward currents from the Arctic Basin supported a marine neritic community, but on the southern and eastern Laptev shelf, in the areas of freshwater influence, brackish-water taxa contributed up to 27% of the total biomass. On the slope and in deep areas a few large Arctic copepod species, Calanus glacialis, C. hyperboreus and Metridia longa, composed the bulk of biomass and determined the pattern of its vertical distribution. The export of Calanus species from the Nansen Basin onto the Laptev shelf appears to be of great importance for the shelf communities. In turn, the eastern outer shelf and slope area of the Laptev Sea are thought to have a pronounced effect on the deep basin, modifying the populations entering the central Arctic. Received: 25 March 1997 / Accepted: 18 July 1997     

The rotifer fauna of arctic sea ice from the Barents Sea,Laptev Sea [2pt] and Greenland Sea

Hydrobiologia - Samples from arctic sea ice were studied for their rotifer fauna. Ice core samples were collected in the northern Barents Sea and the Laptev Sea from August to October 1993 and in...     

Distribution and structure of macrobenthic fauna in the eastern Laptev Sea in relation to environmental factors

The Laptev Sea still ranks among the less known regions of the world’s ocean. Here, we describe the distribution and composition of macrobenthic communities of the eastern shelf and identify key environmental control factors. Samples were collected from dredge catches carried out at 11 stations at depths between 17 and 44 m in August/September 1993 during the TRANSDRIFT I cruise of the Russian R/V “Ivan Kireev.” A total of 265 species were identified from the samples, mostly crustaceans (94). Species numbers per station ranged from 30 to 104. Macrobenthic community distribution clearly showed a depth zonation, consisting of a “Shallow” zone (<20 m), dominated by the crustaceans Mysis oculata (Mysidacea) and Saduria entomon (Isopoda) as well as molluscs, an “Intermediate” zone (20–30 m), characterised by a clear dominance of the bivalve Portlandia arctica, and a “Deep” zone (>30 m) with bivalves P. arctica and Nuculoma bellotii as well as brittle stars Ophiocten sericeum and Ophiura sarsi being most abundant. According to a correlation analysis between faunal and environmental data a combination of duration of ice cover and water depth, respectively, showed the highest affinity to macrobenthic distribution. We conclude that the food input to the benthos, which is largely related to ice-cover regime, and the stress due to the pronounced seasonal salinity variability, which is primarily related to water depth, are prime determinants of macrobenthic community distribution and major causes of the prominent depth zonation in the Laptev Sea. Within the depth zones, sediment composition seems to be most significant in controlling the patterns in the distribution of the benthic fauna.     

Sea Ice-Upper Ocean Ecosystems and Global Changes in the Arctic

In the Arctic, a clear temperature trend toward warming has been observed during the last two decades. The warming has led to a reduction in the area and thickness of the Arctic sea ice cover because of increased melting. Melt water is accumulated within the 0- to 30-m surface layer, markedly changing its hydrological and hydrochemical characteristics: this water is warmer and fresher, with lower nutrient concentrations. A stable thermocline at depths of 30–35 m weakens vertical mixing of water and hampers active exchange between nutrient-enriched water lying below the thermocline and nutrient-poor water under ice. This affects the qualitative and quantitative composition of upper-ocean phyto- and zooplankton. The changes in the climate and the ice environment cause marked alterations in the composition and structure of the biological communities of sea ice and under-ice surface water. Comparative analysis of materials collected in the anticyclonic Arctic Gyre at the ice stations Severnyi Polyus-22 (1975– 1981) and SHEBA (1997–1998) shows that over the last two decades the number of species of ice diatoms markedly decreased and the role of freshwater algae increased. The number of nematodes, copepods, amphipods, and turbellarians, which were the dominant groups in perennial ice, also declined sharply. The results suggest that the sea ice-upper ocean ecosystem is changing from typically marine to brackish-water. The main reason for these changes is probably global warming in the Arctic.     

Biology of Salpa thompsoni in waters adjacent to the Ross Sea, Southern Ocean, during austral summer 2008

Depth-stratified vertical sampling was carried out during the New Zealand International Polar Year cruise to the Ross Sea on board the RV Tangaroa in February–March 2008. The distribution (horizontal and vertical), density and population biology of Salpa thompsoni were investigated. Salps were found at two of the four major sampling locations, e.g. near the continental slope of the Ross Sea and in the vicinity of seamounts to the north of the Ross Sea. Both abundance and biomass of S. thompsoni were highest near the seamounts in the Antarctic Circumpolar Current reaching ~2,500 ind 1,000 m⁻³ and 8.2 g dry wt 1,000 m⁻³ in the water column sampled. The data showed that S. thompsoni populations were able to utilize horizontal and vertical discontinuities in water column structure, in particular the warm Circumpolar Deep Water (CDW), to persist in the high Antarctic. Although salps appeared to continue migrating to the surface colder layers to feed, both aggregate chain and young embryo release seem to be restricted to the CDW. This study for the first time has provided evidence that low Antarctic salp species may successfully reproduce in the hostile high Antarctic realm.     

Diversity and distribution of marine microbial eukaryotes in the Arctic Ocean and adjacent seas

We analyzed microbial eukaryote diversity in perennially cold arctic marine waters by using 18S rRNA gene clone libraries. Samples were collected during concurrent oceanographic missions to opposite sides of the Arctic Ocean Basin and encompassed five distinct water masses. Two deep water Arctic Ocean sites and the convergence of the Greenland, Norwegian, and Barents Seas were sampled from 28 August to 2 September 2002. An additional sample was obtained from the Beaufort Sea (Canada) in early October 2002. The ribotypes were diverse, with different communities among sites and between the upper mixed layer and just below the halocline. Eukaryotes from the remote Canada Basin contained new phylotypes belonging to the radiolarian orders Acantharea, Polycystinea, and Taxopodida. A novel group within the photosynthetic stramenopiles was also identified. One sample closest to the interior of the Canada Basin yielded only four major taxa, and all but two of the sequences recovered belonged to the polar diatom Fragilariopsis and a radiolarian. Overall, 42% of the sequences were <98% similar to any sequences in GenBank. Moreover, 15% of these were <95% similar to previously recovered sequences, which is indicative of endemic or undersampled taxa in the North Polar environment. The cold, stable Arctic Ocean is a threatened environment, and climate change could result in significant loss of global microbial biodiversity.     

Seasonal occurrence of picocyanobacteria in the Greenland Sea and central Arctic Ocean

The seasonal occurrence of picocyanobacteria in the Greenland Sea and Arctic Ocean was investigated during four expeditions in May–June 1987 and 1988, August–October 1991, and November–December 1988 by epifluorescence microscopy. In early summer, the abundance of picocyanobacteria was related to water masses: they were nearly absent in polar water, whereas they occurred in high concentrations (up to 5470 cells ml^–1) in Atlantic Water. During autumn and beginning of winter, the abundances of picocyanobacteria remained around 10³ cells ml^–1. Their relative contribution to total picoplanktonic algal abundance increased from 0% during spring/summer to 70–80% in late autumn, as a result of a decrease in the abundance of eucaryotic picoalgae. Consequently, the impact of picocyanobacteria on Arctic epipelagic carbon and energy flow is of minor importance, and the strong contribution of picoplankton algae to biomass and primary productivity in Arctic seas has to be attributed to eucaryotic species.     

The metazoan meiobenthos along a depth gradient in the Arctic Laptev Sea with special attention to nematode communities

The meiobenthos along a depth transect of oligotrophic sediments in the Arctic Laptev Sea was studied. The meiobenthos followed the general trends reported from other studies: densities decreased with depth in relation to the more limited supply of degradable organic matter at greater depths. Although the sediments along the transect were poor in organic matter in comparison with the NE Atlantic, the densities fitted well with the meiobenthic densities reported from the latter area. It is suggested that the meiobenthos in the cold polar waters is adapted to this extreme environment by a rapid response to short food pulses to the sediments. Nematodes were identified up to genus level and assigned to trophic groups. A total of 32 families comprising 95 genera were found along the transect. The communities were dominated by deposit feeders whose importance increased with depth. Both TWINSPAN and CCA analyses revealed a community shift along the depth transect: a shelf community dominated by Microlaimus and Chromadora could be distinguished from a slope community dominated by Monhystera and Leptolaimus. Generic diversity decreased with depth. Received: 15 March 1997 / Accepted: 29 June 1997     

Biostratigraphic and paleoclimatic significance of a new Pliocene foraminiferal fauna from the central Arctic Ocean

A Pliocene benthic foraminiferal fauna containing a previously unknown species association was found in the basal section of a piston core collected from the crest of Northwind Ridge (NWR) in the central Arctic Ocean. The fauna is dominated by Epistominella exigua, Cassidulina reniforme, Eponides tumidulus, Cibicides scaldisiensis, Lagena spp., Cassidulina teretis, Eponides weddellensis, Bolivina arctica, and Patellina corrugata. The presence of Cibicides scaldisiensis in the assemblage and the occurrence of Cibicides grossus higher in the core are indicative of an early Pliocene age. The morphologically distinctive species Cibicidoides sp. 795 of McNeil (in press) which occurs in the NWR core sample was previously known only from Oligocene through Miocene deposits in the Beaufort-Mackenzie Basin of Arctic Canada. Ehrenbergina sp. A and Cibicidoides aff. C. sp. 795, also present in the core, are new and endemic to the Arctic late Miocene and early Pliocene. These species, and possibly others, are survivors of the late Miocene (Messinian) sea-level crisis, which caused a significant faunal turnover in the Arctic Ocean. The predominantly calcareous assemblage indicates deposition above the calcium carbonate compensation depth in an upper bathyal environment. Paleogeographic affinities for the bulk of the assemblage indicate probable connections between the Arctic and the North Atlantic Oceans, but the endemic species identify environmental differences or partial isolation of the western Arctic Ocean. The species association suggests a cold but milder paleoclimate than that which existed during Pleistocene glacial intervals.     

Composition and distribution of mesozooplankton in the Nansen Basin,Arctic Ocean,during summer

Information about the large-scale zooplankton distribution in the Nansen Basin, that part of the Arctic Ocean most directly influenced by the inflow of Atlantic Water, is still scarce. During the Polarstern expedition ARK IV/3 in July/August 1987 zooplankton from the upper 500 m was sampled along two transects across the western Nansen Basin. Spatial variations in faunal composition, abundance, and biomass are described. Special emphasis is given to the distribution patterns and possible drifting routes of species advected into the Arctic Ocean through Fram Strait. Forty-five species and eight taxa not determined to species level were identified. Copepods clearly dominate in terms of species number, abundance, and biomass. Ostracods and chaetognaths comprise the most important groups of the non-copepod zooplankton. Maximum species numbers were recorded over the abyssal plain around 83°N. Total abundance and biomass decreased by more than 80% towards the northern part of the basin. Cluster analysis revealed two major faunal assemblages, broadly overlapping over the central Nansen Basin, and three principal types of spatial distribution. The well-defined zonation observed in the large-scale zooplankton distribution closely resembles the major hydrographic and topographic features. The opposite movement of the Polar Surface Water and the Atlantic Water in the southern Nansen Basin might cause pronounced deviations between the drifting routes of species with different water mass preferences advected through Fram Strait.     

Sea ice phenology and timing of primary production pulses in the Arctic Ocean

Arctic organisms are adapted to the strong seasonality of environmental forcing. A small timing mismatch between biological processes and the environment could potentially have significant consequences for the entire food web. Climate warming causes shrinking ice coverage and earlier ice retreat in the Arctic, which is likely to change the timing of primary production. In this study, we test predictions on the interactions among sea ice phenology and production timing of ice algae and pelagic phytoplankton. We do so using the following (1) a synthesis of available satellite observation data; and (2) the application of a coupled ice‐ocean ecosystem model. The data and model results suggest that, over a large portion of the Arctic marginal seas, the timing variability in ice retreat at a specific location has a strong impact on the timing variability in pelagic phytoplankton peaks, but weak or no impact on the timing of ice‐algae peaks in those regions. The model predicts latitudinal and regional differences in the timing of ice algae biomass peak (varying from April to May) and the time lags between ice algae and pelagic phytoplankton peaks (varying from 45 to 90 days). The correlation between the time lag and ice retreat is significant in areas where ice retreat has no significant impact on ice‐algae peak timing, suggesting that changes in pelagic phytoplankton peak timing control the variability in time lags. Phenological variability in primary production is likely to have consequences for higher trophic levels, particularly for the zooplankton grazers, whose main food source is composed of the dually pulsed algae production of the Arctic.     

夏季黄海一断面底边界层动物多样性初步研究

2002年8月4日在黄海从青岛至济州岛断面的4个站位上,进行了底边界层动物昼夜连续采样, 对底边界层动物的多样性及其昼夜变化进行了分析。共鉴定出底边界层动物32种, 其中桡足类19种,端足类3种,涟虫3种,糠虾2种,毛颚类2种,枝角类2种,磷虾1种, 可划分为中型浮游动物、大型浮游动物和超底栖动物三个生物类群。主要种类有尖额真猛水蚤(Euterpina acutifrons)、挪威小毛猛水蚤(Microsetella norvegica)、戴氏猛水蚤(Danielssenia sp.)、小拟哲水蚤(Paracalanus parvus)和双刺纺缍水蚤(Acartia bifilosa)等。超底栖动物和中型浮游动物是两个主要类群。此外,桡足类幼体（无节幼体和桡足幼体）也是底边界层动物的重要组成部分。多样性分析显示: 底边界层动物在4个调查站位的均匀度（d）皆较高(0.728-0.915), 但种类较少(19-33), 故多样性指数(H′)较低(2.248-2.827)。超底栖动物的多样性指数相对较高, 中型浮游动物次之, 大型浮游动物较低。各类群的多样性指数在白天和夜间无显著性差异(P>0.05)。底边界层动物的丰度在细砂底质环境的1-3站最低, 在其他3个具有粉砂-粘土底质环境的站位皆较高。通过聚类分析, 可将这两种底质环境上的底边界层动物在26.6%相似性水平上分为两个类群。生物-环境匹配分析显示, 底边界层动物的种类及丰度除了与水深、水温有关外, 还与近底层颗粒有机碳(POC)、颗粒有机氮(PON)的沉降通量以及沉积物中值粒径密切相关。     

Abundance and single-cell activity of heterotrophic bacterial groups in the western Arctic Ocean in summer and winter

Environmental conditions in the western Arctic Ocean range from constant light and nutrient depletion in summer to complete darkness and sea ice cover in winter. This seasonal environmental variation is likely to have an effect on the use of dissolved organic matter (DOM) by heterotrophic bacteria in surface water. However, this effect is not well studied and we know little about the activity of specific bacterial clades in the surface oceans. The use of DOM by three bacterial subgroups in both winter and summer was examined by microautoradiography combined with fluorescence in situ hybridization. We found selective use of substrates by these groups, although the abundances of Ant4D3 (Antarctic Gammaproteobacteria), Polaribacter (Bacteroidetes), and SAR11 (Alphaproteobacteria) were not different between summer and winter in the Beaufort and Chukchi Seas. The number of cells taking up glucose within all three bacterial groups decreased significantly from summer to winter, while the percentage of cells using leucine did not show a clear pattern between seasons. The uptake of the amino acid mix increased substantially from summer to winter by the Ant4D3 group, although such a large increase in uptake was not seen for the other two groups. Use of glucose by bacteria, but not use of leucine or the amino acid mix, related strongly to inorganic nutrients, chlorophyll a, and other environmental factors. Our results suggest a switch in use of dissolved organic substrates from summer to winter and that the three phylogenetic subgroups examined fill different niches in DOM use in the two seasons.     

Evidence of heterotrophic prokaryotic activity limitation by nitrogen in the Western Arctic Ocean during summer

Global warming in the Arctic Ocean may result in changes to the stock and dynamics of nutrients that drive the activity of heterotrophic prokaryotes, a key component of the microbial food web. We performed 14 enrichment experiments during summer in the Beaufort and Chukchi Seas (Western Arctic Ocean), with C (acetate and/or glucose), N (nitrate and/or ammonium) and P (phosphate) amendments. In 8 out of 11 experiments performed with surface waters, prokaryotic heterotrophic production was limited by N, either alone (5 experiments) or in co-limitation with C (3 experiments). This contrasted with the experiments performed using waters from the chlorophyll maxima, where N was never limiting. Diversity analyses (DNA- and RNA-based fingerprinting) suggest that limitation was not restricted to specific operational taxonomic units but common to the different groups. This is the first report of N limitation of prokaryotic heterotrophic production in Arctic surface waters. This control by N may gain importance in future scenarios of higher productivity in the area.     

Environmental influences on benthic fauna associations of the Kara Sea (Arctic Russia)

Macrobenthic faunal associations, hydrography and sediment structure were examined at 14 stations in the Kara Sea. The stations were located in an area influenced by huge runoff from the Ob and Yenisei Rivers and in areas influenced by Barents Sea water. Sampling depths varied from 17 to 43 m, with one station at 195 m. The sediments were predominantly muddy but some stations were sandy. Three hundred and eighty-seven taxa were identified and Polychaeta, Crustacea and Mollusca were the most conspicuous. Species number, abundance and biomass varied widely among stations, and were generally higher in the more marine waters. Boreal-arctic species predominated, but an increase of arctic species from marine to the estuarine areas was evident. Five faunal associations were delineated by cluster analysis and suggested quite heterogeneous sampling areas. The most conspicuous species of each faunal association were Spiochaetopterus typicus, Tridonta borealis, Serripes groenlandicus, Portlandia arctica, and Marenzelleria arctia, respectively. The sedimentation rate, as well as depth, sediment structure and salinity, apparently influenced the main differences in the fauna. Accepted: 29 June 1999     

Phytoplankton dynamics at the ice-edge zone of the Lazarev Sea (Southern Ocean) during the austral summer 1994/1995 drogue study

Phytoplankton dynamics in the open waters of the ice-edge zone of the Lazarev Sea were investigated over 12 consecutive days during a drogue study conducted in austral summer (December/January) 1994/1995. Throughout the study, the upper water column (<30 m) was stratified with a well-defined pycnocline evident. Although a subsurface intrusion of colder, more saline water into the region was recorded on days 5-9 of the experiment, its effect on the water column structure was negligible. Total surface chlorophyll a biomass doubled between days 1 and 5 (from 0.82 to 1.62 mg m^-3), and then showed a tendency to stabilise, while the depth-integrated chlorophyll a standing stock displayed an increasing trend during the entire experiment. All changes in biomass were associated with an increase in microphytoplankton. Flagellates and picoplankton dominated cell counts, while diatoms composed most of the phytoplankton biovolume. Results of the study indicate that, during the period of investigation, average cell abundance decreased. Coupled with this decrease was an increase in the biovolume and average size of the phytoplankton. Phytoplankton succession was observed in the ice edge during the drogue study. Typical ice-associated species of genera Haslea, Fragilariopsis and Chaetoceros, which dominated at the beginning of study, were replaced by open-water species of genera Corethron, Dactyliosolen and Rhizosolenia. The shift in phytoplankton species composition and size can likely be related to high light intensities and grazing by microzooplankton. The intrusion of colder, more saline water on day 5 appeared to modify the diatom succession, indicating extreme variability in phytoplankton dynamics in the near ice-edge zone of the Lazarev Sea.