Experimental evaluation of planktonic respiration response to warming in the European Arctic Sector

The Arctic Ocean is the region on Earth supporting the steepest warming rate and is also particularly vulnerable due to the vanishing ice cover. Intense warming in the Arctic has strong implications for biological activity and the functioning of an Arctic Ocean deprived of ice cover in summer. We evaluated the impact of increasing temperature on respiration rates of surface marine planktonic communities in the European Arctic sector, a property constraining the future role of the Arctic Ocean in the CO₂ balance of the atmosphere. We performed experiments under four different temperature elevation regimes (in situ, +2, +4 and +6°C above the temperature of the sampled water) during cruises conducted in the Fram Strait region and off Svalbard during late fall–early winter, spring and summer. During late fall–early winter, where only three different temperatures were used, no response to warming was observed, whereas respiration rates increased in response to warming in spring and summer, although with variable strength.     

Biogeography and Photosynthetic Biomass of Arctic Marine Pico-Eukaroytes during Summer of the Record Sea Ice Minimum 2012

Information on recent photosynthetic biomass distribution and biogeography of Arctic marine pico-eukaryotes (0.2–3 μm) is needed to better understand consequences of environmental change for Arctic marine ecosystems. We analysed pico-eukaryote biomass and community composition in Fram Strait and large parts of the Central Arctic Ocean (Nansen Basin, Amundsen Basin) using chlorophyll a (Chl a) measurements, automated ribosomal intergenic spacer analysis (ARISA) and 454-pyrosequencing. Samples were collected during summer 2012, the year with the most recent record sea ice minimum. Chl a concentrations were highest in eastern Fram Strait and pico-plankton accounted for 60–90% of Chl a biomass during the observation period. ARISA-patterns and 454-pyrosequencing revealed that pico-eukaryote distribution is closely related to water mass distribution in the euphotic zone of the Arctic Ocean. Phaeocystaceae, Micromonas sp., Dinophyceae and Syndiniales constitute a high proportion of sequence reads, while sequence abundance of autotrophic Phaeocystaceae and mixotrophic Micromonas sp. was inversely correlated. Highest sequence abundances of Phaeocystaceae were observed in the warm Atlantic Waters in Fram Strait, while Micromonas sp. dominated the abundant biosphere in the arctic halocline. Our results are of particular interest considering existing hypotheses that environmental conditions in Nansen Basin might become more similar to the current conditions in Fram Strait. We propose that in response, biodiversity and biomass of pico-eukaryotes in Nansen Basin could resemble those currently observed in Fram Strait in the future. This would significantly alter biogeochemical cycles in a large part of the Central Arctic Ocean.     

International Straits and Trans-Arctic Navigation

The Arctic Ocean is increasingly becoming accessible to international shipping as a result of the reduction in Arctic sea ice. Commercial shipping may seek to transit the Arctic Ocean from either the Pacific or Atlantic Ocean and, as a result, the legal regime of straits has significance for trans-Arctic navigation. In this article, current developments in Arctic shipping are assessed and consideration is given to certain Arctic straits that could prove to be pivotal in future Arctic navigation and shipping. These straits include the Bering Strait, Nares Strait, Davis Strait, Fram Strait, and Denmark Strait.     

Plankton metabolism in the Greenland Sea during the polar summer of 2007

The polar summer metabolism of the planktonic communities in the Greenland Sea was surveyed in July 2007. Planktonic metabolism showed great variability across the studied area, with on average, higher metabolic rates in the Fram Strait-Svalbard region than along the Greenland Current. A significant fraction (47%) of the planktonic communities in the Fram Strait-Svalbard region were net heterotrophic, suggesting that increased respiration rates with further warming may lead the planktonic communities at this region to act as net CO₂ sources. The thresholds gross primary production for metabolic balance (i.e., gross primary production = community respiration) was much higher in the European sector of the Arctic than reported for the Southern Ocean, suggesting that heterotrophic metabolism is more prevalent in the European sector of the Arctic than in the Southern Ocean, indicating high allochthonous inputs in the Arctic region.     

Production and retention of biogenic matter in the southeast Beaufort Sea during 2003�C2004: insights from annual vertical particle fluxes of organic carbon and biogenic silica

Regional variability in the annual fluxes of particulate organic carbon (POC) and biogenic silica (Si) at the periphery of the Mackenzie Shelf (Beaufort Sea) was investigated using eight long-term sediment traps moored at ~100-m depth. Relatively high autochthonous POC and Si fluxes were recorded in the Mackenzie Trough (4.1 and 8.9 g m⁻² year⁻¹ respectively) and off Cape Bathurst (6.6 and 79 g m⁻² year⁻¹), two areas where upwelling events are frequently observed. Diatomaceous new production was minimum on the mid-slope of the Mackenzie Shelf (2.8 g C m⁻² year⁻¹), moderate in the Mackenzie Trough (14.5 g C m⁻² year⁻¹), and highest off Cape Bathurst (128.7 g C m⁻² year⁻¹). High annual autochthonous POC flux corresponded to high diatom production. Among sites, the vertical attenuation of the POC flux increased with diatomaceous new production. Hence, the retention of autochthonous POC in the surface layer (<100 m) was highest (95%) at the highly productive site off Cape Bathurst, intermediate (72%) in the moderately productive Mackenzie Trough, and low (4%) at the unproductive mid-slope of the shelf. Our results indicate that, on Arctic shelves, upwelling and the production of diatoms increase the fraction of the POC which is retained in the surface layer and diverted to the pelagic food web. In the relatively unproductive waters of the Arctic Ocean, biological hot spots such as the one identified off Cape Bathurst where the food web promotes retention rather than vertical export could be disproportionately important as feeding grounds for higher trophic levels.     

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     

Comparing marine mammal acoustic habitats in Atlantic and Pacific sectors of the High Arctic: year-long records from Fram Strait and the Chukchi Plateau

During the International Polar Year (IPY), acoustic recorders were deployed on oceanographic moorings in Fram Strait and on the Chukchi Plateau, representing the first coordinated year-round sampling of underwater acoustic habitats at two sites in the High Arctic. Examination of species-specific marine mammal calls recorded from autumn 2008–2009 revealed distinctly different acoustic habitats at each site. Overall, the Fram Strait site was acoustically complex compared with the Chukchi Plateau site. In Fram Strait, calls from bowhead whales (Balaena mysticetus) and a variety of toothed whales (odontocetes) were recorded year-round, as were airgun pulses from seismic surveys. In addition, calls from blue whales (Balaenoptera musculus) and fin whales (B. physalus) were recorded from June to October and August to March, respectively. Conversely, at the Chukchi Plateau site, beluga (Delphinapterus leucas) and bowhead whale calls were recorded primarily from May to August, with airgun signals detected only in September–October. Ribbon seal (Phoca fasciata) calls were detected in October–November, with no marine mammals calls at all recorded from December to February. Of note, ice-adapted bearded seals (Erignathus barbatus) were recorded at both sites, primarily in spring and summer, corresponding with the mating season for that species. Differences in acoustic habitats between the two sites were related to contrasts in sea ice cover, temperature, patterns of ocean circulation and contributions from anthropogenic noise sources. These data provide a provisional baseline for the comparison of underwater acoustic habitats between Pacific and Atlantic sectors of the High Arctic.     

Living planktonic foraminifera in the Fram Strait (Arctic): absence of diel vertical migration during the midnight sun

The timing of vertical migration in planktonic foraminifera (ex. ontogenetic, diel) is still an open debate. This work aims to investigate the diel vertical migration (DVM) of Neogloboquadrina pachyderma (N. pachyderma) and Turborotalita quinqueloba (T. quinqueloba) in the Arctic during the midnight sun. N. pachyderma and T. quinqueloba dominate the total assemblage in the cold Polar Water and warmer North Atlantic Water masses, respectively. Foraminifera were collected at several depths along the Fram Strait. Afterwards sampling was performed at the same station for 24 h at continuous and discrete time intervals. Results show no evidence of planktonic foraminifera DVM since there was no significant variability in the abundance and size distribution during the 24-h collection period. This finding provides information to improve the interpretation of foraminifera in paleoclimatic works. This is especially relevant in the Fram Strait as paleoclimatic studies in this region are fundamental to investigating the history of the Atlantic water inflow into the Arctic Ocean.     

Increased sea ice melt as a driver of enhanced Arctic phytoplankton blooming

Phytoplankton primary production in the Arctic Ocean has been increasing over the last two decades. In 2019, a record spring bloom occurred in Fram Strait, characterized by a peak in chlorophyll that was reached weeks earlier than in other years and was larger than any previously recorded May bloom. Here, we consider the conditions that led to this event and examine drivers of spring phytoplankton blooms in Fram Strait using in situ, remote sensing, and data assimilation methods. From samples collected during the May 2019 bloom, we observe a direct relationship between sea ice meltwater in the upper water column and chlorophyll a pigment concentrations. We place the 2019 spring dynamics in context of the past 20 years, a period marked by rapid change in climatic conditions. Our findings suggest that increased advection of sea ice into the region and warmer surface temperatures led to a rise in meltwater input and stronger near-surface stratification. Over this time period, we identify large-scale spatial correlations in Fram Strait between increased chlorophyll a concentrations and increased freshwater flux from sea ice melt.     

Phytoplankton community structure during the record Arctic ice-melting of summer 2007

In the summer of 2007, the Arctic Ocean experienced the largest loss of ice cover yet observed. We examined the phytoplankton community composition at several stations in the NE Arctic Sector during the ATOS-Arctic cruise in July 2007, specifically in the Fram Strait and along the permanent ice edge up to 81°N. The prymnesiophyte Phaeocystis pouchetti, present exclusively in its colonial form, dominated the whole phytoplankton community, representing 82.1 ± 3.1% (mean ± SE) of the phytoplankton biovolume in the region. Diatoms, small flagellates and dinoflagellates, expected to dominate the ice-melt waters in this sector of the Arctic Ocean, were practically insignificant, representing 7.3 ± 2.4%, 6.8 ± 1.4% and 4.4 ± 1.2% of phytoplankton biovolume, respectively. The fraction of the phytoplankton biomass that comprised diatoms increased with increasing water temperature and salinity, and was, therefore, negatively associated with the increased load of ice-melt waters. In contrast, the fraction of the biomass that comprised P. pouchetii was not as clearly related to temperature and had a weak tendency to decrease with increasing temperature. This pattern was likely the result of different populations stress, as the percentage of living cells of P. pouchetii increased with increasing salinity and temperature. The exceptional dominance of the colonial form of P. pouchetii during the massive ice losses of summer 2007 provides indication of major changes in phytoplankton community structure and carbon flow with climate change in the Arctic Ocean.     

Response of benthic microbial communities to chitin enrichment: an in situ study in the deep Arctic Ocean

In situ enrichment experiments were carried out in the Arctic deep sea (Fram Strait region) to observe the response of benthic microbial communities to chitin supply. Chambers of a benthic lander were filled in July 2004 with deep-sea sediments enriched with 1.3–7.0 g m⁻² of chitin and the effects of chitin enrichment were assessed on the microbial hydrolytic activity potential, cell number and community structure after periods of 1 week and 1 year of in situ deployment. The input of chitin had no effect on microbial abundance and chitobiase activity after 7 days of incubation, whereas community structure in enriched sediments, determined by terminal restriction fragment length polymorphism analysis of 16S rRNA genes, was different from the controls. After 1 year, microbial numbers and activity significantly increased in sediments enriched with high chitin concentrations and bacterial community structure was different from that of the other treatments. The present study suggests that microbial community structure in Arctic deep-sea sediments can react quickly to sudden large chitin inputs into the sediments and that this appears to precondition subsequent enhanced growth and enzymatic activity changes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Metazoan meiofauna dynamics and pelagic–benthic coupling in the Southeastern Beaufort Sea,Arctic Ocean

Pelagic–benthic coupling is relatively well studied in the marginal seas of the Arctic Ocean. Responses of meiofauna with regard to seasonal pulses of particulate organic matter are, however, rarely investigated. We examined the dynamics of metazoan meiofauna and assessed the strength of pelagic–benthic coupling in the Southeastern Beaufort Sea, during autumn 2003 and spring–summer 2004. Meiofauna abundance varied largely (range: 2.3 × 10⁵ to 5 × 10⁶ ind m⁻²), both spatially and temporally, and decreased with increasing depth (range: 24–549 m). Total meiofauna biomass exhibited similar temporal as well as spatial patterns as abundance and varied from 25 to 914 mg C m⁻². Significant relationships between sediment photopigments and various representatives of meiofauna in summer and autumn likely indicate the use of sediment phytodetritus as food source for meiofauna. A carbon-based grazing model provided estimates of potential daily ingestion rates ranging from 32 to 723 mg C m⁻². Estimated potential ingestion rates showed that meiofauna consumed from 11 to 477% of the sediment phytodetritus and that meiofauna were likely not food-restricted during spring and autumn. These results show that factors governing the distribution and abundance of metazoan meiofauna need to be better elucidated if we are to estimate the benthic carbon fluxes in marginal seas of the Arctic Ocean. This paper is dedicated to the memory of our dear friend and colleague Gaston Desrosiers who contributed so much to benthic ecology. We will continue in his spirit.     

Records of the gadoid fish <Emphasis Type="Italic">Arctogadus glacialis</Emphasis> (Peters, 1874) in the European Arctic

The Arctogadus glacialis is endemic to the Arctic Ocean and its apparently disjunct circumpolar distribution range from the Siberian coast through the Chukchi Sea and the Canadian Arctic to the shelf off NE Greenland. Records of A. glacialis are scarce in the European Arctic and here we present all available and reliable records of the species in the area. Altogether, 296 specimens of A. glacialis are reported from 53 positions in the European Arctic during the period 1976–2008. The specimens were registered off Iceland and the Jan Mayen Island, northwest and northeast of Svalbard, northeast in the Barents Sea, and south and east off Franz Josef Land. The additional records show that A. glacialis display a circumpolar and more continuous distribution than described before. In the European Arctic, A. glacialis has been caught at 155–741 m depth with the highest abundance at 300–400 m. We therefore suggest that A. glacialis is more associated to the continental shelves surrounding the Arctic Ocean than previously thought. The length–weight relation of A. glacialis is similar across the European Arctic.     

Recent research on Arctic benthos: common notions need to be revised

Increased public awareness of the global significance of polar regions and opening of the Russian Arctic to foreign researchers have led to a pronounced intensification of benthic research in Arctic seas. The wealth of information gathered in these efforts has markedly enhanced our knowledge on the Arctic benthos. While some scientific concepts have been corroborated by the novel findings (e.g., low endemism and high faunistic affinity to northern Atlantic assemblages), other common notions need to be revised, particularly with regard to the often-cited differences between Arctic seas and the Southern Ocean. It has been demonstrated that benthos assemblages vary broadly in diversity between Arctic regions and that, hence, the idea of a consistently poor Arctic benthos—being in stark contrast to the rich Antarctic bottom fauna—is an undue overgeneralization. In terms of biogeographic diversity, both Arctic and Antarctic waters seem to be characterized by intermediate species richness. Levels of disturbance—a major ecological agent known to heavily affect benthic diversity and community structure—have been assumed to be relatively high in the Arctic but exceptionally low in the Southern Ocean. The discovery of the great role of iceberg scouring in Antarctic shelf ecosystems, which has largely been overlooked in the past, calls for a reconsideration of this notion. The novel data clearly demonstrate that there are marked differences in geographical and environmental setting, impact of fluvial run-off, pelagic production regime, strength of pelago–benthic coupling and, hence, food supply to the benthos among the various Arctic seas, impeding the large-scale generalization of local and regional findings. Field evidence points to the great significance of meso-scale features in hydrography and ice cover (marginal ice zones, polynyas, and gyres) as ‘hot spots’ of tight pelago–benthic coupling and, hence, high benthic biomass. In contrast, the importance of terrigenic organic matter discharged to the Arctic seas through fluvial run-off as an additional food source for the benthos is still under debate. Studies on the partitioning of energy flow through benthic communities strongly suggest that megafauna has to be adequately considered in overall benthic energy budgets and models of carbon cycling, particularly in Arctic shelf systems dominated by abundant echinoderm populations. Much progress has been made in the scientific exploration of the deep ice-covered Arctic Ocean. There is now evidence that it is one order of magnitude more productive than previously thought. Therefore, the significance of shelf–basin interactions, i.e., the importance of excess organic carbon exported from productive shelves to the deep ocean, is still debated and, hence, a major topic of on-going research. Another high-priority theme of current/future projects are the ecological consequences of the rapid warming in the Arctic. Higher water temperatures, increased fluvial run-off and reduced ice cover will give rise to severe ecosystem changes, propagating through all trophic levels. It is hypothesized that there would be a shift in the relative importance of marine biota in the overall carbon and energy flux, ultimately resulting in a switch from a ‘sea-ice algae–benthos’ to a ‘phytoplankton–zooplankton’ dominance.     

Summertime primary production and carbon export in the southeastern Beaufort Sea during the low ice year of 2008

Following the extreme low ice year of 2007, primary production and the sinking export of particulate and gel-like organic material, using short-term particle interceptor traps deployed at 100 m, were measured in the southeastern Beaufort Sea during summer 2008. The combined influence of early ice retreat and coastal upwelling contributed to exceptionally high primary production (500 ± 312 mg C m⁻² day⁻¹, n = 7), dominated by large cells (>5 μm, 73% ± 15%, n = 7). However, except for one station located north of Cape Bathurst, the sinking export of particulate organic carbon (POC) was relatively low (range: 38–104 mg C m⁻² day⁻¹, n = 12) compared to other productive Arctic shelves. Estimates indicate that 80% ± 20% of the primary production was cycled through large copepods or the microbial food web. Exopolymeric substances were abundant in the sinking material but did not appear to accelerate POC sinking export. The use of isotopic signatures (δ¹³C, δ¹⁵N) and carbon/nitrogen ratios to identify sources of the sinking material was successful only at two stations with a strong marine or terrestrial signature, indicating the limitations of this approach in hydrographically and biologically complex Arctic coastal waters such as in the Beaufort Sea. At these two stations influenced by either coastal upwelling or erosion, the composition and magnitude of particulate sinking fluxes were markedly different from other stations visited during the study. These observations underscore the fundamental role of mesoscale circulation patterns and hydrodynamic singularities on the export of particulate organic material on Arctic shelves.     

The impact of ice melting on bacterioplankton in the Arctic Ocean

Global warming and the associated ice melt are leading to an increase in the organic carbon in the Arctic Ocean. We evaluated the effects of ice melt on bacterioplankton at 21 stations in the Greenland Sea and Arctic Ocean in the summer of 2007, when a historical minimum of Arctic ice coverage was measured. Polar Surface Waters, which have a low temperature and low salinity and originate mainly from melted ice, contained a very low abundance of bacteria (7.01 × 10⁵ ± 2.20 × 10⁵ cells ml⁻¹); however, these bacteria had high specific bacterial production (2.40 ± 1.61 fmol C bac⁻¹ d⁻¹) compared to those in Atlantic Waters. Specifically, bacterioplankton in Polar Surface Waters showed a preference for utilizing carbohydrates and had significantly higher specific activities of the glycosidases assayed, i.e. β-glucosidase, xylosidase, arabinosidase and cellobiosidase. Furthermore, bacterioplankton in Polar Sea Waters showed preferential growth on some of the carbohydrates in the Biolog Ecoplate, such as d-cellobiose and N-acetyl-d-glucosamine. Our results suggest that climate change and the associated melting of Arctic ice might induce changes in bacterioplankton functional diversity by enhancing the turnover of carbohydrates. Since organic aggregates are largely composed of polysaccharides, higher solubilization of aggregates might modify the carbon cycle, weaken the biological pump and have biogeochemical and ecological implications for the future Arctic Ocean.     

Picoeukaryote Plankton Composition off West Spitsbergen at the Entrance to the Arctic Ocean

Investigation of marine eukaryotic picoplankton composition is limited by missing morphological features for appropriate identification. Consequently, molecular methods are required. In this study, we used 454‐pyrosequencing to study picoplankton communities at four stations in the West Spitsbergen Current (WSC; Fram Strait). High abundances of Micromonas pusilla were detected in the station situated closest to Spitsbergen, as seen in surveys of picoplankton assemblages in the Beaufort Sea. At the other three stations, other phylotypes, affiliating with Phaeocystis pouchetii and Syndiniales in the phylogenetic tree, were present in high numbers, dominating most of them. The picoplankton community structures at three of the stations, all with similar salinity and temperature, were alike. At the fourth station, the influence of the East Spitsbergen Current, transporting cold water from the Barents Sea around Spitsbergen, causes different abiotic parameters that result in a significantly different picoeukaryote community composition, which is dominated by M. pusilla. This observation is particularly interesting with regard to ongoing environmental changes in the Arctic. Ongoing warming of the WSC could convey a new picoplankton assemblage into the Arctic Ocean, which may come to affect the dominance of M. pusilla.     

Ethological analysis of the trace fossil Zoophycos: hints from the Arctic Ocean

Löwemark, L. 2011: Ethological analysis of the trace fossil Zoophycos: Hints from the Arctic Ocean. Lethaia, Vol. 45, pp. 290–298. The distribution of the trace fossil Zoophycos in Quaternary marine sediments from the Arctic Ocean was studied in twelve piston and gravity cores retrieved during the Swedish icebreaker expeditions YMER80, Arctic Ocean‐96 and LOMROG I & II. The sampled cores span an area from the Makarov Basin to the Fram Strait. Zoophycos was only found in two cores taken at more than 2 km water depth on the slope of the Lomonosov Ridge, but was absent in cores obtained at shallower depth, confirming earlier observations of the trace maker’s bathymetric preferences. The two cores containing Zoophycos are characterized by quiet sedimentation and slightly enhanced food flux compared with the general Arctic. The occurrence of Zoophycos in these cores in a setting that is characterized by extreme seasonal variations in food flux due to the total ice coverage during winters and high primary productivity during the long summer days, is interpreted to be a cache‐behaviour response to pulsed flux of food to the benthic realm. □Arctic Ocean, ethology, Quaternary, spreiten, trace fossils, Zoophycos.     

New Production Regulates Export Stoichiometry in the Ocean

The proportion in which carbon and growth-limiting nutrients are exported from the oceans’ productive surface layer to the deep sea is a crucial parameter in models of the biological carbon pump. Based on >400 vertical flux observations of particulate organic carbon (POC) and nitrogen (PON) from the European Arctic Ocean we show the common assumption of constant C:N stoichiometry not to be met. Exported POC:PON ratios exceeded the classical Redfield atomic ratio of 6.625 in the entire region, with the largest deviation in the deep Central Arctic Ocean. In this part the mean exported POC:PON ratio of 9.7 (a:a) implies c. 40% higher carbon export compared to Redfield-based estimates. When spatially integrated, the potential POC export in the European Arctic was 10–30% higher than suggested by calculations based on constant POC:PON ratios. We further demonstrate that the exported POC:PON ratio varies regionally in relation to nitrate-based new production over geographical scales that range from the Arctic to the subtropics, being highest in the least productive oligotrophic Central Arctic Ocean and subtropical gyres. Accounting for variations in export stoichiometry among systems of different productivity will improve the ability of models to resolve regional patterns in carbon export and, hence, the oceans’ contribution to the global carbon cycle will be predicted more accurately.     

Activity and biomass of the small benthic biota under permanent ice-coverage in the central Arctic Ocean

Sediment samples collected during the expedition “Arctic Ocean `96” with the Swedish ice-breaker ODEN were investigated to estimate for the first time heterotrophic activity and total microbial biomass (size range from bacteria to small metazoans) from the perennially ice-covered central Arctic Ocean. Benthic activities and biomass were evaluated analysing a series of biogenic sediment compounds (i.e. bacterial exoenzymes, total adenylates, DNA, phospholipids, particulate proteins). In contrast to the very time-consuming sorting, enumeration and weight determination, analyses of biochemical sediment parameters may represent a useful method for obtaining rapid information on the ecological situation in a given benthic system. Bacterial cell numbers and biomass were estimated for comparison with biochemically determined biomass data, to evaluate the contribution of the bacterial biomass to the total microbial biomass. It appeared that bacterial biomass made up only 8–31% (average of all stations = 20%) of the total microbial biomass, suggesting a large fraction of other small infaunal organisms within the sediment samples (most probably fungi, yeasts, protozoans such as flagellates, ciliates or amoebae, as well as a fraction of small metazoans). Activity and biomass values determined within this study were generally extremely low, and often even slightly lower than those given for other deep oceanic regions, thus characterizing the seafloor of the central Arctic Ocean as a “benthic desert”. Nevertheless, some clear trends in the data could be found, e.g. generally sharply decreasing values within the sediment column, a vague tendency for declining values with increasing water depth of sampling stations, and also differences between various Arctic deep-sea regions. Received: 16 May 1997 / Accepted: 28 August 1997