Northeast Water Polynya Research Articles

Spatial and temporal distribution patterns of benthic foraminifera in the Northeast Water Polynya, Greenland

Abundance, biofacies and ATP content of benthic foraminifera (>63 μm) were studied in the Northeast Water (NEW) Polynya (77–81°N, 5–17°W) over the ice-free summer, 1993, to investigate how a polynya system might influence the underlying benthic community. In the living assemblage, distinguished by Rose Bengal staining, over 60 taxa could be identified. The biofacies identified was similar to that of other Arctic shelf habitats. Foraminifera were counted in 3 size fractions (63–125 μm, 125–250 μm and >250 μm), with 65% of the foraminifera occurring in the smallest size fraction (63–125 μm). Total abundances (>63 μm) in the uppermost 1 cm averaged approximately 200 ind/10 cm3 and declined down-core, as did the number of species. Abundances and species composition correlated positively with sediment chlorophyll and ATP content, with maxima occurring in the shallower northern regions of the polynya, suggesting a general dependence on food. Foraminera biomass was estimated to be 0.1-0.3 g Corg/m2. Abundances, biomass and ATP content were comparable to ice-free, deep-sea regions in the Norwegian Sea. Temporal changes observed over a 2 month period at one location were difficult to distinguish from spatial and analytical variability. Contrary to expectations, growth was unpronounced at the community and at a species level, implying either a delayed response of the benthic foraminiferal community to food inputs from the overlying water column or the presence of biological limitations other than food, such as predation.

Winter intensification and water mass evolution from yearlong current meters in the Northeast Water Polynya

In the summer of 1992, four current meter moorings were deployed in and later retrieved from the Northeast Water (NEW) polynya on the East Greenland Shelf by the USCGC Polar Sea. The moorings provided hourly temperature, salinity and current data for approximately one year. In the NEW, the circulation intensified and steadiness increased during winter. This intensification was most readily observed at 150 m on the southern side of Westwind trough. The surface layer freshened from summer through December due to ice-melt and freshwater runoff mixing down to at least 75 m. From December through early spring, salinity increased probably due to brine rejected during ice formation. Wintertime events showed water at 75 m with temperatures at the freezing point. Knee Water (KW) was not observed in the current meter data. However, a warmer and fresher than KW watermass was observed at 150 m over the shelf and may result from mixing outside the NEW among KW and the major water masses influencing the region. Polar Water and Atlantic Intermediate Water. Several short-lived events of 3 to 7 days duration perturbed the T-S character at each of the current meters. We believe that these T-S shifts were anticyclonic eddies advecting through the NEW polynya. During such perturbations, T-S values found generally at 75 m were observed at 150 m and T-S values generally at 150 m were observed at 250 m. On the northern side of the Westwind trough, the current meter data provided direct evidence for westward flow into the western extent of the trough at a depth of 250 m. This southwesterly current along the northwest slope of the trough at 250 m is in agreement with the summertime ADCP measurements made in 1992 aboard Polar Sea, and is consistent with the flow inferred from summer hydrography measured from Polarstern in 1993.

The water mass characteristics of the Northeast Water Polynya: Polar Sea data 1992–1993

Hydrographic cruises in the summers of 1992 and 1993 were carried out in the North-East Water (NEW) Polynya. For both years, CTD casts on the NEW Polynya shelf area yielded a signature of a highly homogeneous, cold (θ = −1.74°C) and relatively fresh (S = 32.40 ppt) water just below the surface pycnocline, which we refer to as the Northeast Water Polynya Intermediate Water (PyIW). Its homogeneity, its location and the fact that its core temperature is very close to the freezing point all suggest that this water is formed convectively through a loss of buoyancy to the atmosphere over the open portions of the Polynya. The source waters are the low salinity surface waters found in the northern sector of the Polynya area. The thickness of the PyIW varied from 10 to 60 m throughout the northern (Norske-Westwind through system) and central (Belgica Bank) portion of shelf region. It was not found over the slope nor in Belgica Trough immediately to the south. A volumetric θ-S analysis of the PyIW demonstrated that it suffered a small loss between the two years and that its areal distribution and core water type remained virtually constant. Some qualitative assessments are made concerning its formation and loss. The small interannual variability of the PyIW layer implies a high residence time that has important physical and biological repercussions. The summer modification of the Polynya surface waters is also discussed; and by relating the water-type change with the summer heat budget, estimates of 47 and 75 cm were made for the amount of ice thinning occurring over the area for the two years, respectively. The water found below the sills (at ∼265 m) of the Norske-Westwind Trough system has a warmer (θ = 0.78°C) and saltier (S = 34.83 ppt) water type, than that of the PyIW, which characterizes it as a species of return Atlantic Intermediate Water.

Distribution and exchange of water masses in the Northeast Water polynya (Greenland Sea)

On the basis of classical hydrographic and nutrient analysis, water masses and their spreading in the Northeast Water (NEW) Polynya were investigated from RV Polarstern ARK IX (1993) data. It is shown that a local water body, East Greenland Shelf Water, occupies the top layer in the NEW and that this water is different from Polar Water exported from the Arctic Polar Ocean. Polar Water, as well as the underlying and also imported Knee Water, follows a path crossing the broad East Greenland Shelf diagonally from northeast to southwest but both waters do not enter the NEW Polynya. Intermediate waters in the NEW are also modified locally. A local source of silicate, contributing to an intermediate silicate maximum in the trough system, is identified in the centre of the anticyclonic movement over Belgica Bank. Furthermore, it is confirmed that there is no one-directional through-flow of deeper waters in the trough system. Belgica Trough and Westwind Trough contain two different water types of Atlantic origin, which are not directly related to Return Atlantic Waters. The deeper waters in Norske Trough are supplied from Belgica Trough over a sill of about 250 m depth.

Distribution of zooplankton in the Northeast Water Polynya during summer 1992

Abstract The distribution and abundances of zooplankton in the Northeast Water (NEW) Polynya during the summer of 1992 have been determined from samples collected with Bongo (this study) and MOCNESS (earlier analysis) plankton net tows. The initial hypothesis was that the troughts of the Greenland Shelf in the region of the NEW polynya would be conduits for the infusion of zooplankton species of Arctic and North Atlantic origin on to the shelf. Analysis of MOCNESS tows indicated instead that advection of zooplankton onto the shelf in the polynya region was limited, resulting in low abundances of the large herbivores in the polynya. The distribution of zooplankton determined from the 43 Bongo tows reported here strengthen this finding. Low abundances of the large herbivorous copepods and of other primarily herbivorous zooplankton taxa were observed throughout the ice-free region, in contrast to higher abundances observed further to the east in Westwind Trough or in the south in Belgica Trough. Cluster analysis was used to identify groups of co-occurring zooplankton taxa and groups of stations with similar relative compositions of zooplankton taxa. The community composition of the Belgica Trough was distinctly different from that observed in northern regions, with high abundances of open ocean copepods ( Calanus finmarchicus and C. hyperboreus ). Two types of communities were identified in the northern regions: one typical of the eastern basin (Westwind Trough) and one typical of the western basin (Norske Trough) of the northern trough. The relationship between the different zooplankton communities and the water mass characteristics was not conclusive; however, it did appear that zooplankton populations had been advected in the upper water column into the Westwind Trough from north of the study area. The low abundances of herbivorous taxa in the ice free region supported previous estimates that meso-macro zooplankton may not be significant consumers of primary production in the polynya.

Autotrophic flagellates and diatoms in the Northeast Water polynya, Greenland: summer 1993

Abundance, biomass and distribution of autotrophic flagellates, autotrophic dinoflagellates and diatoms were measured in the Northeast Water (NEW) Polynya during summer, 1993, using epifluorescence microscopy (EFM) and high-pressure liquid chromotography (HPLC). Numerous discrepancies existed between results from EFM and HPLC. Phytoplankton communities determined microscopically at the depth of the chlorophyll maximum consisted primarily of flagellates in various size classes (average 1.3 × 107 cells 1−1, 8.5 μg Cl−1) and the small diatom Chaetoceros socialis (average 5×106 cells 1−1, 52 μg Cl−1), with subsurface maxima of both groups usually occurring close to the nitricline. A wide variety was observed in the composition of the phytoplankton community with respect to biomass of individual taxa. The biomass of autotrophic flagellates represented on average 23% of the total autotrophic biomass in all regions of the study area as defined by water mass type. Based on carbon units derived from pigment concentrations (HPLC), prasinophytes and haptophytes each contributed 24% to total flagellate (non-dinoflagellate) biomass and chrysophytes contributed 52%. In the northeast quadrant, influenced by the East Greenland Current, haptophyte contribution dropped to 9%. Most of the biomass of autotrophic flagellates was in cells < 8 μm in diameter; of diatoms, in cells < 10 μm in diameter. Highest picoplankton biomass (cells < 2 μm) occurred in ice-free water at moderate stability. The average contribution of autotrophic dinoflagellates to total autotrophic biomass was 6% (3 μg Cl−1, 1.7×105 cells 1−1). Ratios of microscopically measured autotrophic carbon to fluorometric chlorophyll a (i.e. community C:chl a) ranged from 11–265 (avg. 61), with maximum ratios attributable to regions dominated by C. socialis. Although differences between four areas of the NEW with respect to physical characteristics of the water column were observed, few corresponding biological differences could be verified. Similarly, phytoplankton community composition was weakly if at all correlated with physical or chemical characteristics of the water column. Future investigations should examine food web dynamics (i.e. grazing) and small-scale circulation to account for the mosaic pattern of phytoplankton features.

Sediment community biomass and respiration in the Northeast water polynya, Greenland: a numerical simulation of benthic lander and spade core data

Sediment community metabolism (oxygen demand) was measured in the Northeast Water (NEW) polynya off Greenland employing two methods: in situ benthic chambers deployed with a benthic (GOMEX) lander and shipboard laboratory Batch Micro-Incubation Chambers (BMICs) utilizing ‘cores’ recovered from USNEL box cores. The mean benthic respiration rate measured with the lander was 0.057 mM O2 m−2 h−1 (n = 5); whereas the mean measured with the BMICs was 0.11 mM O2 m−2 h−1 (n = 21; p < 0.01 that the means were the same). In terms of carbon fluxes (14 and 27 mg C m−2 d−1), these respiration rates represent ca. 5–15% of the average net primary production measured in the euphotic zone in 1992. The biomass of the bacteria, meiofauna and macrofauna were measured at each location to quantify the relationship between total community respiration and total community biomass (mean 1.42 g C m−2). Average carbon residence time in the biota, calculated by dividing the biomass by the respiration, was on the order of 50–100 days, which is comparable to relatively oligotrophic continental margins at temperate latitudes. The biomass and respiration data for the aerobic heterotrophic bacteria, the infaunal invertebrates (meiofauna and macrofauna), and the epifaunal megabenthos (two species of brittle stars) are summarized in a ‘steady-state’ solution of a sediment food chain model, in terms of carbon. This carbon budget illustrates the relative importance of the sediment-dwelling invertebrates in the benthic subsystem, compared to the bacteria and the epibenthos, during the summer open-water period in mud-lined troughs at depths of about 300 m. The input needed to drive heterotrophic respiratory processes was within the range of the input of organic matter recorded in moored, time-sequencing sediment traps. A time-dependent numerical simulation of the model was run to investigate the potential responses of the three size groups of benthos to abrupt seasonal pulses of particulate organic matter. The model suggests that there is a time lag in the increase in bottom community biomass and respiration following the POC pulse, and provides hypothetical estimates for the potential carbon storage in the summer (open water), followed by catabolic losses during each ensuing winter (ice covered). This sequence of storage and respiration may contribute to the process of seasonal CO2 ‘rectification’ (sensu Yager et al., 1995) in some Arctic ecosystems.

Tritium-3He ages of deep waters in the NEW Polynya

Abstract The measurements of tritium and helium isotopes in the Northeast Water (NEW) Polynya region in the summer of 1992 and 1993 show that the deep waters in the north (Westwind Trough) are 3–5 years older than those in the south (Belgica Trough). The distribution of these tracers in the region indicates that a deep ‘flushing’ event took place between the 1992 and 1993 field studies. This result corroborates information obtained by others from hydrographic data and from year-long bottom-moored current meters.

Meroplankton abundance in the Northeast Water Polynya: Insights from oceanographic parameters and benthic abundance patterns

Abstract We investigated meroplankton (planktonic larvae of benthic organisms) abundance and distribution in the Northeast Water (NEW) Polynya, located on the northeast coast of Greenland, from July 15 to August 15, 1992. Meroplankton was present at all sites visited (0.03–84.83 individuals per m 3 ); at one station meroplankton comprised 8.28% of total zooplankton. Total meroplankton abundance was correlated with total zooplankton abundance and total benthic infaunal abundance but was not correlated with either microscopic carbon concentration or primary productivity. Examination of distribution data for barnacle nauplii and adults indicated that both adults and larvae were concentrated at the same locations. Patterns of distribution were also examined for stelleroid plutei, polychaete larvae and trochophores. There were distinct geographic patterns in total and class-specific meroplankton distributions, with maximal abundances occurring over the Belgica Bank and in the eastern regions of the Westwind Trough and minimal abundances in the Belgica Trough. The apparent control of meroplankton distribution by the hydrography of the region, coupled with the correlation between meroplankton, zooplankton and adult infaunal abundance, reinforces the hypothesis that hydrography plays a major role in controlling the distribution of biota in the NEW polynya (Ambrose and Renaud, 1995; Ashjian et al., 1995, 1997-this volume; Smith et al., 1995; Piepenburg et al., 1997-this volume).

Distribution of diatoms in the Northeast Water Polynya, Greenland

This study formed part of the Northeast Water project (NEW project) which dealt with physical, geophysical and biological processes in the Northeast Water Polynya off Northeast Greenland. This was part of the International Arctic Polynya Programme (IAPP). The diatom composition of the water masses, sea ice and melt ponds was analysed to show the relationship between ice and the water column near the ice with regard to the origin and fate of the cells in the ice and melt ponds. Fragilariopsis oceanica, Fragiliria sp. I and Chaetoceros socialis usually dominated the phytoplankton, while the ice and melt pond samples showed a wide range of assemblages, with different single-celled pennates and two undescribed species, Navicula sp. 1 and Nitzschia sp. 1 often dominant. Planktonic algae in sea ice can be released into the water column during ice break-up and melt, thus contributing to the spring bloom in the water column, if the timing of the release and the species composition are correct. The number of different ice algal assemblages supports the theory that cells originated from the water column, the benthos and freshwater. In addition, differential growth in the sea ice or melt ponds often altered the relative abundance of species in comparison with what is usually found in their original habitat. However, many of the cells in the ice and melt ponds were dead (empty frustules), making it difficult to determine whether the cells had actually lived in these habitats.

New production in the Northeast Water Polynya: 1993

The Northeast Water Polynya has been suggested as acting as a sink for carbon, especially during the spring and summer when phytoplankton growth is active. During 1993 the polynya was sampled for the entire growing period (late May through mid-August) in order to more accurately assess the magnitude, controls and patterns of new and total (ammonium, nitrate and urea) nitrogen production. This represents the first assessment of new production throughout an entire season in the Arctic. We found that, in 1993, new production, based on 15N-tracer techniques and integrated over the euphotic zone, was 0.141 mmol N m−2 h−1 (0.361 g C m−2 d−1 when converted using observed C/N ratios). Measured f ratios averaged 0.65 and demonstrate that the system, to a great extent, was using nitrate as a nitrogen source. In general f ratios were greatest early in the season and minimal in mid-summer. Urea uptake was highly variable and contributed slightly less than ammonium to phytoplankton nitrogen demand. Nitrate uptake at stations with low (< 0.5μM) nitrate concentrations was significantly reduced, implying that nitrate concentrations limited phytoplankton growth late in the growing season. Long-term new production rates calculated from nutrient depletion patterns from the polynya as a whole as well as a time-series constructed from a single location were ca. 0.144-0.281 g C m−2 d−1. The relationship between new production as measured by incubations and nutrient depletion budgets suggests that phytoplankton growth is the dominant factor influencing the nitrogen budget of the polynya. The amount of material available for removal from the euphotic zone is limited and constrains the degree to which the polynya can act as a regional carbon sink.

Does a pulsed food supply to the benthos affect polychaete recruitment patterns in the Northeast Water Polynya?

Abstract Recently, researchers have discovered that deep-sea species from many phyla exhibit distinct seasonality in reproductive effort. Many of these studies describe the seasonality as correlating with pulsed sedimentation of phytodetritus to the benthos. The Northeast Water Polynya provides an ideal system in which to test whether a compressed season of pelagic productivity corresponds to recruitment patterns in benthic organisms. We took sediment cores at a station nine times between 30 May and 11 August 1993 and assessed seasonal patterns in recruitment and benthic pigment concentration. Two distinct, but compositionally different, peaks in benthic pigment concentration were observed during this period. While total polychaete recruitment showed a broad mid-summer peak in intensity, at the taxonomic level of family and below, peaks were sharper and suggested seasonal recruitment events. No support, however, was identified for synchrony of reproduction with pulses of sedimenting food from the water column, indicating that food limitation does not explain reproductive patterns in this region. Trophic dynamics, including differential feeding, predation, and survival patterns among recruits, may provide a mechanism for the observed lag time between pulses of food and recruitment, but additional study is required to resolve the determining factors.

Benthic community patterns reflect water column processes in the Northeast Water polynya (Greenland)

Abstract Benthic community patterns were investigated in the Northeast Water polynya (Greenland) during the summers of 1992 and 1993 to elucidate to what extent the bottom fauna is influenced by the dynamics of the overlying water. Five different fractions of the benthos (foraminiferans, nematodes, polychaetes, peracarid crustaceans, and epibenthic megafauna), ranging in average adult body size over 6 orders of magnitude (from about 100 μm to about 10 cm), were sampled quantitatively at 69 stations in water depths from 40 to 515 m. Total abundances of nematodes, polychaetes and peracarid crustaceans were found to be primarily correlated with parameters characterizing the potential benthic food supply (water column pigment and nitrate concentrations, sediment bound pigments and sediment biological activity), whereas abundances of foraminiferans and megabenthos were largely associated with seabed properties. Four benthic zones were distinguished by separately analyzing the faunistic composition and distribution of the five community fractions for Ob Bank, Western Westwind Trough, Eastern Westwind Trough, and Belgica Trough. This pattern was shown principally to reflect pelagic regimes differing in surface water hydrography, ice cover and euphotic productivity. This is the first time that a synoptic study of several benthic community portions spanning such a range in sizes and life styles has been performed in a polar shelf ecosystem. Our results indicate that abundances as well as composition of Arctic benthos are largely influenced by mesoscale pelagic processes, and thus provide further evidence for the importance of the benthic-pelagic coupling in high latitude seas.

210Pb and 239,240Pu in the Northeast Water Polynya, Greenland: particle dynamics and sediment mixing rates

Abstract Distributions of the radionuclides 210Pb and 239,240Pu in sediment cores from the Northeast Water Polynya, Greenland, showed that these nuclides reached depths of 5–15 cm by particle mixing and sediment accumulation. End-member average values of the particle mixing coefficient and sediment accumulation rate were 0.13 cm2 y−1 and 0.06 cm y−1, obtained from the 210Pb profiles by assuming that each process is dominant relative to the other. Both 210Pb and 239,240Pu were measured on four cores; using the Pu data to constrain mixing rates produced corrected sediment accumulation rates that were 20–80% of the values calculated by neglecting mixing. Organic carbon burial in the polynya sediments was ≤0.4 mmol m−2 d−1, based on measured POC values at depth in the sediments and sediment accumulation rates corrected for mixing. This value is about 1% of the independently measured POC flux leaving the euphotic zone and compares with benthic carbon remineralization rates of 7% calculated by others from O2 uptake in the sediments. The inventories of excess 210Pb in the sediments ranged from 6 to 28 dpm cm−2. Relative to the atmospheric input of 210Pb and in situ production from decay of 226Ra, approximately 5 dpm cm−2 of 210Pb was being removed from the water column. The difference between the removal from the water column and sediment inventories suggests a net import of 210Pb to the polynya. This may occur by input of dissolved 210Pb from offshore waters or by input of 210Pb carried by sea ice. Particulate matter in land-derived fast ice adjacent to the polynya contained 330 ± 14 dpm of excess 210Pb g−1. If particles transported in sea ice are comparable to those extracted from fast ice, then sea ice transport into the polynya followed by melting may be an important source of excess 210Pb to the area. Fast ice also may contribute 210Pb if portions break off and melt within the polynya, as occurred in 1993.

Annual fluxes of particulate chemical trace compounds during the North-East water polynya experiment

Particulate fluxes of organic marker substances (alkanes, wax esters, pristane, and alkenones) and trace elements (Al, Cd, Cu, Fe, Mn, Ni, and Pb) were determined from identical samples of sediment trap material collected at North East Water Polynya (NEWP) locations E and F in the north-western Greenland Sea. Samples from the East Greenland Shelf were obtained with two sediment traps deployed at 130 m depth over a 331-day period from August 1992 to June 1993 within the NEWP experiment. Particulate fluxes of the chemical tracers showed a pronounced seasonality, which was largely consistent with ice-coverage data. Relative flux pattern exhibited initial maxima during August and September 1992. Fluxes were lowest during winter time (November 1992 to early March 1993), followed by an increase by a factor of 2–5 in mid-March 1993. In contrast, flux of n -alkanes occurred almost entirely in spring 1993. Flux of alkenones was not detectable throughout this experiment. Temporal variations of chemical tracer fluxes at trap location E were similar to those of station F during autumn 1992. Normalization calculations showed that lithogenic material was an important source for trace element fluxes, with an estimated lithogenic fraction of the bulk material flux increasing from autumn to spring. A non-lithogenic flux component was observed for Cd throughout the time of deployment. The chemical data indicate that during the peak flux periods a large proportion of the sinking particles consisted of fresh material. Differences in the patterns of the bulk material flux and the chemical tracer fluxes indicate that there must have been a substantial difference between autumn and spring in the gross chemical composition of the sinking material.

Nutrient status of the Northeast Water Polynya

The nutrient distribution in the Northeast Water Polynya (NEW) was investigated intensively between the end of May and the beginning of August 1993 during the R/V Polarstern cruise ARK IX. The major characteristics were low initial nitrate concentrations (ca. 4 μM) in the surface mixed layer of the East Greenland Shelf Water, accompanied by high silicate values (ca. 10–14 μM). These concentrations were not reduced by phytoplankton growth. Silicate was rather homogeneously distributed in the entire water column, whereas nitrate increased continuously with depth to about 13 μM. Phosphate concentrations were about 1.1 μM and had a similar distribution to that of silicate. During the course of the summer, nutrients became depleted, and nitrate was exhausted in large parts of the NEW. Silicate was reduced to values of less than 2 μM at some stations which implies that diatom growth continued despite nitrate depletion, ammonium serving as a nitrogen source. The polynya is fertilised by water with the initial nutrient concentrations downstream of the Norske Oer Ice Shelf. This process continuously supplies nutrients to the surface throughout the year and these are transported northward by the anticyclonic surface circulation following the topography of the trough system. The northern boundary of this tongue of relatively nutrient-rich water is controlled by the uptake of nutrients by phytoplankton in summer. Its extemsion is variable due to interactions between biological processes, circulation and ice cover. In the Ob Bank region the nutrient distribution can be altered by the inflow of Polar Water from the north when strong northerly winds prevail as happened during the first part of the study.

Summary of the Northeast Water Polynya formation and development (Greenland sea)

Abstract The mechanisms forming the Northeast Water Polynya (NEWP), located on the shelf northeast of Greenland, are elaborated for different sub-domains of the polynya for the years 1990–1993. Sea-ice formation, sea-ice melt and the horizontal divergence of ice-floe velocity owing to winds and currents are investigated for the sub-domains. Several shelf-ice barriers of different size extend perpendicular to prevailing currents and winds causing a divergence of the ice-field flow in their lee. In summer, winds are weak and the northwand flowing coastal current in combination with Norske Oer Shelf Ice (NOSI) constitutes the dominant forcing of the Northeast Water summer polynya forming in the southern part of the NEW area. During this season the polynya gradually increases its size towards the north since the air-sea heat budget is positive then and now ice-formation takes place. In winter, strong northerly wind outbreaks push newly formed sea-ice out of Ob Bank region in the northern NEW area which is sheltered by Ob Bank Shelf Ice (OBSI) and the eastern coast of Kronprins Christians Land. Since during the winter season the air-sea temperature difference can amount to up to 30°C new ice forms rapidly balancing the ice export.

Spatial distribution of particle composition and microbial activity in benthic boundary layer (BBL) of the Northeast Water Polynya

Heterotrophic activity and related measures of pelagic microorganisms were studied in the Northeast Water Polynya, (NEWP 77–82°N, 10–15°W) in 1993 during a FS Polarstern cruise. A bottom water sampler (BWS), which enabled collection of distinct 12 1 water samples at variable heights above the seabed, was used to study the distribution of various biological parameters with high vertical resolution in the benthic boundary layer (BBL). Samples were taken in the water column from varying depths in the intermediate water column (IWC) down to 5 m above bottom using a CTD as well as at 40, 20, 12 and 7 cm above the sea bed using the bottom water sampler. Total suspended matter, particulate organic carbon and nitrogen (POC, PON), chlorophyll a equivalents (chl. a equiv.), bacterial abundance and size distribution and microbial activity were determined in each of the samples. Most of the deep samples (IWC and BBL, maximum water depth 479 m) came from warmer Atlantic influenced water that fills a circular trough system on the northeast Greenland shelf. In general the activity of the microbial community, cell-specific activity and concentrations of POC and chl. a equiv. were significantly higher in the BBL compared to the IWC. Microbial activity appeared to be independent of the quantity of available POC, indicating the nutritional importance of dissolved organic matter for microorganisms. The spatial distribution of particle composition and microbial activity in the BBL was strongly determined by the anticyclonic current pattern and the spatial pattern of primary production in the polynya. Close coupling of biological processes in the surface waters and particle composition and microbial activity in the BBL were found below areas of fluctuating ice cover and above 260 m water depth in the northeastern Westwind Trough. Highest microbial activity occurred in the heavily ice covered Belgica Trough, although only remnants of freshly produced organic matter were present. In the open polynya near-bottom particle properties were mainly determined by lateral advection. The benthic boundary layer is shown to represent a distinct environment, with small scale vertical distribution of particle properties and stimulated microbial activity, indicating that rapid modification of organic matter occurs in the BBL before its final incorporation into the sediment.

Glaciation, climate history, changing marine levels and the evolution of the Northeast Water polynya

Abstract The morphology of the bank- and trough system in the Northeast Water (NEW) polynya area is to a large extent a result of glacial erosion and deposition by an extended Inland Ice which reached the continental shelf. The last deglaciation of the fjords and forelands adjacent to the polynya took place shortly before 9000 radiocarbon yr B.P. At that time the marine level stood 80 m higher than today, which meant a water depth over much of the Ob Bank and parts of the Belgica Bank twice as deep as presently. This probably gave the East Greenland Current a more unimpeded southward flow, with less eddy effects. In combination with the generally warmer climate of the early Holocene (with less ice coming out of the Polar Basin, a larger influx of Atlantic Water leading to more ice melting in the NEW area, and probably no ice drift hindering fast-ice barrier in the south), this probably meant that no polynya existed at that time. Instead there was a more general open water summer situation. After 5000 yr B.P. climate deteriorated and glaciers expanded. As the isostatic rise of land and near coast bottoms continued, resulting in shallowing banks, both the bathymetric and climatic situation responsible for the existence of today's polynya gradually came into existence. The shallowing Ob Bank began to obstruct ice drift from the north and an ice-drift hindering fast-ice barrier was created in the south. But even after 500 yr B.P. it is likely that shorter spells of more generally open water existed, during which marine based paleoeskimos (Independence II) and neoeskimos (Thule) immigrated along the at other times totally ice-bound coasts of North Greenland.

Flux of particulate matter through copepods in the Northeast water polynya

Particulate organic carbon (POC) and nitrogen (PON) production by large calanoid copepods was investigated on the northeast Greenland shelf during August 1992 and May to August 1993. Both Calanus hyperboreus and C. glacialis females, when suspended in seawater collected from the chlorophyll maximum, produced about 40 pellets per day, which contained a carbon and nitrogen content equivalent to 8% and 6% of body carbon, respectively, and 2% of body nitrogen. In experiments, the carbon:nitrogen (C:N) ratio by weight of suspended particulates, C. hyperboreus, and fecal pellets was 6.7, 7.7 and 28.5, respectively. The unusually high C:N ratio for pellets, in part, may be attributed to elevated ratios of > 20μm size fractions of particulate organic matter, the size fraction more common in the diet of these large copepods and the fraction dominated by diatoms according to microscopic and pigment data. The implied elevated C:N ratios of large phytoplankton cells were probably due to nitrogen deficiency, as shown by other studies in this region. In addition, female C. hyperboreus appeared to be more efficient in assimilating nitrogen than carbon, which also would have contributed to high C:N ratios in egested pellets. Unfractionated POC concentrations explained 54% of the variability in carbon egestion and 70% of the variability in nitrogen egestion in copepods, whereas copepod body content accounted for little of the variation on the short time scales of the experiments. Carbon egestion by C. hyperboreus was positively correlated with POC concentrations at the depth of the chlorophyll maximum, while nitrogen egestion was negatively correlated with PON concentrations in the euphotic zone. Estimates of potential community egestion rates for the upper water column indicate that copepods represent a major pathway of organic carbon transformation in this Arctic shelf system. On average, copepods may have ingested 45% of the primary production and egested fecal matter equivalent to 20% of the carbon and 12% of the nitrogen particulate flux sedimenting from the surface layer. However, several lines of evidence suggest that pellets were remineralized in the water column and, hence, may have contributed little organic carbon and nitrogen to the benthos.