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1.
The shallow continental shelves and slope of the Amerasian Arctic are strongly influenced by nutrient-rich Pacific waters advected over the shelves from the northern Bering Sea into the Arctic Ocean. These high-latitude shelf systems are highly productive both as the ice melts and during the open-water period. The duration and extent of seasonal sea ice, seawater temperature and water mass structure are critical controls on water column production, organic carbon cycling and pelagic–benthic coupling. Short food chains and shallow depths are characteristic of high productivity areas in this region, so changes in lower trophic levels can impact higher trophic organisms rapidly, including pelagic- and benthic-feeding marine mammals and seabirds. Subsistence harvesting of many of these animals is locally important for human consumption. The vulnerability of the ecosystem to environmental change is thought to be high, particularly as sea ice extent declines and seawater warms. In this review, we focus on ecosystem dynamics in the northern Bering and Chukchi Seas, with a more limited discussion of the adjoining Pacific-influenced eastern section of the East Siberian Sea and the western section of the Beaufort Sea. Both primary and secondary production are enhanced in specific regions that we discuss here, with the northern Bering and Chukchi Seas sustaining some of the highest water column production and benthic faunal soft-bottom biomass in the world ocean. In addition, these organic carbon-rich Pacific waters are periodically advected into low productivity regions of the nearshore northern Bering, Chukchi and Beaufort Seas off Alaska and sometimes into the East Siberian Sea, all of which have lower productivity on an annual basis. Thus, these near shore areas are intimately tied to nutrients and advected particulate organic carbon from the Pacific influenced Bering Shelf-Anadyr water. Given the short food chains and dependence of many apex predators on sea ice, recent reductions in sea ice in the Pacific-influenced sector of the Arctic have the potential to cause an ecosystem reorganization that may alter this benthic-oriented system to one more dominated by pelagic processes.  相似文献   

2.
The uptake of atmospheric carbon dioxide in the water transported over the Bering–Chukchi shelves has been assessed from the change in carbon-related chemical constituents. The calculated uptake of atmospheric CO2 from the time that the water enters the Bering Sea shelf until it reaches the northern Chukchi Sea shelf slope (1 year) was estimated to be 86±22 g C m−2 in the upper 100 m. Combining the average uptake per m3 with a volume flow of 0.83×106 m3 s−1 through the Bering Strait yields a flux of 22×1012 g C year−1. We have also estimated the relative contribution from cooling, biology, freshening, CaCO3 dissolution, and denitrification for the modification of the seawater pCO2 over the shelf. The latter three had negligible impact on pCO2 compared to biology and cooling. Biology was found to be almost twice as important as cooling for lowering the pCO2 in the water on the Bering–Chukchi shelves. Those results were compared with earlier surveys made in the Barents Sea, where the uptake of atmospheric CO2 was about half that estimated in the Bering–Chukchi Seas. Cooling and biology were of nearly equal significance in the Barents Sea in driving the flux of CO2 into the ocean. The differences between the two regions are discussed. The loss of inorganic carbon due to primary production was estimated from the change in phosphate concentration in the water column. A larger loss of nitrate relative to phosphate compared to the classical ΔN/ΔP ratio of 16 was found. This excess loss was about 30% of the initial nitrate concentration and could possibly be explained by denitrification in the sediment of the Bering and Chukchi Seas.  相似文献   

3.
As part of the 2002 Western Arctic Shelf–Basin Interactions (SBI) project, spatio-temporal variability of dissolved inorganic carbon (DIC) was employed to determine rates of net community production (NCP) for the Chukchi and western Beaufort Sea shelf and slope, and Canada Basin of the Arctic Ocean. Seasonal and spatial distributions of DIC were characterized for all water masses (e.g., mixed layer, halocline waters, Atlantic layer, and deep Arctic Ocean) of the Chukchi Sea region during field investigations in spring (5 May–15 June 2002) and summer (15 July–25 August 2002). Between these periods, high rates of phytoplankton production resulted in large drawdown of inorganic nutrients and DIC in the Polar Mixed Layer (PML) and in the shallow depths of the Upper Halocline Layer (UHL). The highest rates of NCP (1000–2850 mg C m−2 d−1) occurred on the shelf in the Barrow Canyon region of the Chukchi Sea and east of Barrow in the western Beaufort Sea. A total NCP rate of 8.9–17.8×1012 g for the growing season was estimated for the eastern Chukchi Sea shelf and slope region. Very low inorganic nutrient concentrations and low rates of NCP (<15–25 mg C m−2 d−1) estimated for the mixed layer of the adjacent Arctic Ocean basin indicate that this area is perennially oligotrophic.  相似文献   

4.
In the late 1950s, Soviet researchers collected benthic infaunal samples from the southeastern Bering Sea shelf. Approximately 17 years later, researchers at University of Alaska Fairbanks also sampled the region to assess infaunal biomass and abundance. Here, the two data sets were examined to document patterns and reveal any consistent differences in infaunal biomass among major feeding groups between the two time periods. No significant differences in the geometric mean biomass of all taxa pooled were indicated between the two study periods (1958–1959=49.1 g m−2; 1975–1976=60.8 g m−2; P=0.14); however, significant differences were observed for specific functional groups, namely carnivores, omnivores and surface detritivores. Of the 64 families identified from both data sets from all functional groups, 21 showed statistically significant (P0.05) differences in mean biomass. Of the 21 families showing significant differences, 19 (91%) of the families had higher mean biomass in the 1975–1976 data set. The above differences suggest a trend toward higher overall infaunal biomass for specific functional groups during mid 1970s compared with the late 1950s. Temperature measurements and literature data indicate that the mid-1970s was an unusually cold period relative to the period before and after, suggesting a mechanistic link between temperature changes and infaunal biomass. Food-web relationships and ecosystem dynamics in the southeastern Bering Sea indicate that during cold periods, infaunal biomass will be elevated relative to warm periods due to elevated carbon flux to the benthos and exclusion of benthic predators on infaunal invertebrates by the cold bottom water on the shelf. As long-term observations of temperature and sea-ice cover indicate a secular warming trend on the Bering Sea shelf, the potential changes in food-web relationships could markedly alter trophic structure and energy flow to apex consumers, potentially impacting the commercial, tourist and subsistence economies.  相似文献   

5.
Shelf–basin exchange in the western Arctic was evaluated by use of water-column analyses of 228Ra/226Ra ratios and the first measurements of the short-lived 224Ra (T1/2=3.64 d) in the Arctic. During the 2002 shelf–basin interaction (SBI) program, excess 224Ra was detected over the shelf but was not found seaward of the shelf-break. Similarly, the 228Ra/226Ra ratio dropped rapidly from the shelf across the shelf-break. Consequently, the model age gradient (elapsed time since shelf residence) northward across the Chukchi Shelf increased from 1–5 years nearshore to approximately 14 years in surface waters sampled off shelf at the southern margin of the Beaufort Gyre. This steep gradient is consistent with very slow exchange between the Chukchi Shelf and the Beaufort Gyre, whereby Bering Strait inflow is constrained by the Earth's rotation to follow local isobaths and does not easily move into deeper water. The strong dynamic control inhibiting water that enters the system through Bering Strait from flowing north across isobaths also would lead to a long recirculation time of river water emptied into the Beaufort Gyre. Possible mechanisms that can generate cross-shelf currents that break the topographic constraint to follow isobaths, and thereby transport water (and associated properties) off the shelves include wind-induced upwelling/downwelling, meandering jets, and eddies. Evidence of such a process was found during the ICEX project in the Beaufort Sea in April 2003 when excess 224Ra was measured over 200 km from any shelf source. This required an NE offshore flow of 40 cm s−1 assuming that the source water derives from the mouth of Barrow Canyon. A weak northeastward flow was measured using an LADCP within the upper 300 m of the ocean, but was of lower speed than required by the 224Raxs at the time of the ICEX occupation.  相似文献   

6.
Sediment-laden sea ice is widespread over the shallow, wide Siberian Arctic shelves, with off-shelf export from the Laptev and East Siberian Seas contributing substantially to the Arctic Ocean's sediment budget. By contrast, the North American shelves, owing to their narrow width and greater water depths, have not been deemed as important for basin-wide sediment transport by sea ice. Observations over the Chukchi and Beaufort shelves in 2001/02 revealed the widespread occurrence of sediment-laden ice over an area of more than 100,000 km2 between 68 and 74°N and 155 and 170°W. Ice stratigraphic studies indicate that sediment inclusions were associated with entrainment of frazil ice into deformed, multiple layers of rafted nilas, indicative of a flaw-lead environment adjacent to the landfast ice of the Chukchi and Beaufort Seas. This is corroborated by buoy trajectories and satellite imagery indicating entrainment in a coastal polynya in the eastern Chukchi Sea in February of 2002 as well as formation of sediment-laden ice along the Beaufort Sea coast as far eastward as the Mackenzie shelf. Moored upward-looking sonar on the Mackenzie shelf provides further insight into the ice growth and deformation regime governing sediment entrainment. Analysis of Radarsat Synthetic Aperture (SAR) imagery in conjunction with bathymetric data help constrain the water depth of sediment resuspension and subsequent ice entrainment (>20 m for the Chukchi Sea). Sediment loads averaged at 128 t km–2, with sediment occurring in layers of roughly 0.5 m thickness, mostly in the lower ice layers. The total amount of sediment transported by sea ice (mostly out of the narrow zone between the landfast ice edge and waters too deep for resuspension and entrainment) is at minimum 4×106 t in the sampling area and is estimated at 5–8×106 t over the entire Chukchi and Beaufort shelves in 2001/02, representing a significant term in the sediment budget of the western Arctic Ocean. Recent changes in the Chukchi and Beaufort Sea ice regimes (reduced summer minimum ice extent, ice thinning, reduction in multi-year ice extent, altered drift paths and mid-winter landfast ice break-out events) have likely resulted in an increase of sediment-laden ice in the area. Apart from contributing substantially to along- and across-shelf particulate flow, an increase in the amount of dirty ice significantly impacts (sub-)ice algal production and may enhance the dispersal of pollutants.  相似文献   

7.
In the spring and summer of 2002 primary production in the Chukchi Sea was measured, using 14C uptake experiments. Our cruise track encompassed the shelf and continental slope area of the Chukchi and Beaufort Seas progressing into deep water over the Canada Basin. The study area experienced upwards of 90% ice cover during the spring, with ice retreating into the basin during the summer. Production in the spring was light-limited due to ice cover, with average euphotic zone production rates of <0.3 g C m−2 d−1. Values of 8 g C m−2 d−1 were observed in association with surface bloom conditions during the initial ice breakup. Considerable nutrient reduction in the surface waters took place between the spring and summer cruise, and although not observed, this was attributed to a spring bloom. Decreased ice cover and increased clarity of surface waters in the summer allowed greater light penetration. The highest rates of production during the second cruise were found at 25–30 m, coincident with the top of the nutricline. Daily euphotic zone productivity in the summer averaged 0.78 g C m−2 d−1 on the shelf and 0.32 g C m−2 d−1 on the edge of the Canada basin. These data provide an estimated annual production of 90 g C m−2 yr−1 in the study area.  相似文献   

8.
Acoustic data and net samples were collected during late spring and early fall 1997–1999 to assess zooplankton and micronekton abundance and distribution relative to the Inner Front at three sampling grids (Port Moller, Cape Newenham and Nunivak Island) on the inner shelf of the southeast Bering Sea. Epibenthic scattering layers were observed during May–June and August–September in all three years. Acoustic data were scaled to euphausiid biomass using target strength models. Mean euphausiid biomass determined acoustically for each transect line was 0.7–21 g m−2, with most values below 5 g m−2. There was no consistent relationship between the distribution and biomass of euphausiids and the location of the Inner Front. Zero age pollock were observed on the inner shelf in August–September during all years, but were confined primarily to the stratified side of the Inner Front and to the frontal regime. The acoustic data for pollock were scaled to biomass using laboratory measurements of gas bladder dimensions and target strength models. Acoustic determinations of mean transect biomass for euphausiids did not differ from literature values for the inner shelf of the southeast Bering Sea, and pollock biomass on the inner shelf did not differ from that around the Pribilof Islands. Despite recent anomalies in climate and oceanographic conditions on the inner shelf, and high mortality of shorttail shearwaters during 1997, we found no evidence of significant interannual differences in the biomass of euphausiids or zero-age pollock on the inner shelf of the southeast Bering Sea.  相似文献   

9.
A key goal of the Western Arctic Shelf Basin Interactions program is to understand how physical and biological processes together impact shelf–basin exchange of biological, chemical, and physical properties. High-resolution vertical distributions of plankton and particles were obtained using an Auto Video Plankton Recorder from 29 locations on the Chukchi Shelf, in the deep Beaufort Sea, and across the Beaufort–Chukchi Shelf-break during a cruise on the USCGC Healy in July–August, 2002. Coincident velocity estimates were collected using hull-mounted acoustic Doppler current profilers. Images of plankton and particles were extracted automatically and identified manually to taxa and type. Copepods, diatom chains, decaying diatoms, marine snow, and radiolarians were the most abundant categories observed. Distinct regional differences in abundance were observed that were associated with different oceanographic regimes and with the prevailing circulation in the region. Vertical distributions were closely associated with the physical structure of the water column. A sharp horizontal discontinuity in abundance of all categories between shelf and basin was observed, located over the shelf break and potentially established and maintained by transport of plankton and particles along-shelf to the east rather than northwards towards the basin. Barrow Canyon and the shelf and shelf-break east of Barrow Canyon had very high concentrations of plankton and particles, especially marine snow, that may have resulted from elevated production on the eastern Chukchi Shelf that subsequently was advected out of Barrow Canyon and to the east. Comparisons of downward flux, estimated from particle sinking rates based on individual marine snow particle size, and horizontal velocities suggested that much of the marine snow carbon was sinking to the benthos of the Chukchi Sea prior to being advected off-shelf. Velocities and plankton concentrations together indicated that little off-shelf flux of plankton or particles to the basin was occurring except in an eddy located off of the Beaufort Shelf.  相似文献   

10.
The ampeliscid amphipod community in the Chirikov Basin of the northern Bering Sea was a focus of study during the 1980s because they were a major food for the Eastern North Pacific (ENP) population of gray whales Eschrichtius robustus. Information from the 1980s benthic investigations, published accounts of ENP gray whale population trends and the occurrence in 1999–2000 of an unusual number of gray whale mortalities prompted concern that the whale population may have exceeded the carrying capacity of its food base. Therefore, during two cruises per year between June and September, 2002 and 2003, we resampled the 20 stations occupied during the 1980s, to determine if there had been any significant changes in ampeliscid abundance and biomass. During 2002–2003, average ampeliscid dry weight biomass was about 28±10 g m−2 (95% confidence interval), a decline of nearly 50% from maximum values in the 1980s. Amphipod length measurements indicated that the declines were due mainly to the absence of the larger animals (20–30 mm length). Two hypotheses were considered regarding the amphipod declines: gray whale predation and climate. Ampeliscid production (105 kcal m−2 yr−1) and gray whale energy requirements (1.6×108 kcal individual−1 yr−1) indicated that as little as 3–6% of the current estimate of the ENP gray whale population could remove 10–20% of the annual ampeliscid production from the study site in 2002–2003, a finding consistent with the hypothesis that top-down control by foraging whales was the primary cause of the observed declines. A 10-yr time series of temperature near the bottom in the Bering Strait and northward transport did not reveal a consistent trend between 1990 and 2001, suggesting that climate influences were not the major cause of the observed declines. Arctic ampeliscids have slow growth rates and long generation times; therefore the ampeliscid community may require decades to recover to densities observed in the 1980s. Predicted warming trends in the northern Bering Sea could impact ampeliscid recovery by lowering primary production or altering the community composition of the benthos.  相似文献   

11.
The phytoplankton community was studied in Bering Strait and over the shelf, continental slope, and deep-water zones of the Chukchi and Beaufort seas in the middle of the vegetative season (July–August 2003). Its structure was analyzed in relation to ice conditions and the seasonal patterns of water warming, stratification, and nutrient concentrations. The overall ranges of variation in phytoplankton abundance and biomass were estimated at 2.0 × 102 to 6.0 × 106 cells/l and 0.1 to 444.1 mg C/m3. The bulk of phytoplankton cells concentrated in the seasonal picnocline, at depths of 10–25 m. The highest values of cell density and biomass were recorded in regions influenced by the inflow of Bering Sea waters or characterized by intense hydrodynamics, such as the Bering Strait, Barrow Canyon, and the outer shelf and slope of the Chukchi Sea. In the middle of the vegetative season, the phytoplankton in the study region of the Western Arctic proved to comprise three successional (seasonal) assemblages, namely, the early spring, late spring, and summer assemblages. Their spatial distribution was dependent mainly on local features of hydrological and nutrient regimes rather than on general latitudinal trends of seasonal succession characteristic of arctic ecosystems.  相似文献   

12.
We analyzed the taxonomic structure and spatial variability of phytoplankton abundance and biomass in the Chukchi and Beaufort Seas during spring and summer seasons of the SBI program. Phytoplankton samples were collected during two surveys from May 10 to June 13 and from July 19 to August 21 of 2002. In May and June, ice cover exceeded 80% over most of the study area and there was no vertical stratification, indicating that the successional state of the phytoplankton corresponded to the end of the winter biological season. The phytoplankton abundance ranged from a few tens to a few thousands of cells per liter, while biomass varied from 0.1 to 3.0 mg C m−3. Small areas of high phytoplankton abundance (0.13–1.3×106 cells L−1) and biomass (22–536 mg C m−3), dominated by early spring diatoms Pauliella taeniata and Fragilariopsis oceanica in the surface waters, which indicated the beginning of the spring bloom, were observed only in the southeastern part of the Chukchi shelf and off Point Barrow. In July and August summer period, more than a half of the study area had <50% ice cover and the water column was stratified by temperature and salinity. Over the Chukchi shelf and continental slope of the Beaufort Sea, the phytoplankton abundance and biomass were an order of magnitude higher in July–August than in May–June. The taxonomic diversity of algae also increased due to the appearance of late-spring and summer diatoms, dinoflagellates, and coccolithophorids (Emiliania huxleyi). Interestingly, the seasonal differences between phytoplankton abundance and taxonomic composition in the spring and summer periods varied the least over the Chukchi Sea slope and in the deep-water area of the Arctic Ocean. High algae concentrations in summer were located in the lower layers of the euphotic zone, suggesting that the spring bloom on both the Chukchi shelf and in the western part of the Beaufort Sea occurred in late June/early July. In the spring and summer, the microalgal community was characterized by a high abundance of 4–10 μm flagellates, which exceeded the abundance of all other taxonomic groups. In both seasons studied, phytoplankton reached its maximum abundance within restricted areas in the southern part of the Chukchi Sea southwest of Point Hope, in the northern part of the Chukchi shelf between the 50- and 100-m isobaths, on the shelf northwest of Point Barrow, and over the continental slope in the Beaufort Sea. The pronounced spatial difference in the seasonal state was a characteristic feature of the phytoplankton community in the western Arctic.  相似文献   

13.
CHEMTAX analysis of high-performance liquid chromatography(HPLC) pigment was conducted to study phytoplankton community structure in the northern Bering Sea shelf, where a seasonal subsurface cold pool emerges. The results showed that fucoxanthin(Fuco) and chlorophyll a(Chl a) were the most abundant diagnostic pigments, with the integrated water column values ranging from 141 to 2 160 μg/m2 and 477 to 5 535 μg/m2, respectively. Moreover, a diatom bloom was identified at Sta. BB06 with the standing stock of Fuco up to 9 214 μg/m3. The results of CHEMTAX suggested that the phytoplankton community in the northern Bering Sea shelf was dominated by diatoms and chrysophytes with an average relative contribution to Chl a of 80% and 12%, respectively, followed by chlorophytes, dinoflagellates, and cryptophytes. Diatoms were the absolutely dominant algae in the subsurface cold pool with a relative contribution exceeding 90%, while the contribution of chrysophytes was generally higher in oligotrophic upper water. Additionally, the presence of a cold pool would tend to favor accumulation of diatom biomass and a bloom that occurred beneath the halocline would be beneficial to organic matter sinks, which suggests that a large part of the phytoplankton biomass would settle to the seabed and support a rich benthic biomass.  相似文献   

14.
We have developed and run a model with sufficiently high resolution (9 km and 45 levels) and a large enough spatial domain to allow for realistic representation of flow through the narrow and shallow straits in the northern Bering Sea. This is potentially important for quantification of long-term mean and time-dependent ocean circulation, and water mass and property exchanges between the Pacific and Arctic Oceans. Over a 23 year interval (1979–2001), mean transport through Bering Strait is estimated to be 0.65 Sv. Comparison of our model results with published observations indicates that ocean circulation is not only variable at seasonal to interdecadal scales but it is also responsive to short-term atmospheric forcing. One of such events occurred during the winter of 2000–2001 with reversed oceanic flow in some areas and much reduced sea-ice cover. Analyses of eddy kinetic energy fields identify some high biological productivity regions of the Chirikov Basin coincident with persistent high energy (up to 2700 cm2 s−2 in the surface layer and up to 2600 cm2 s−2 at mid-depth) throughout the annual cycle. Model output in the Bering Strait region is validated against several time series of moored observations of water mass properties. Comparison with shipboard observations of near-bottom salinity from late winter through autumn indicates that the model reasonably represents the major water-mass properties in the region. The modeled vertical water-column structure in the northern Bering Sea allows increased understanding of the mechanisms of water transformation and transport northward through Bering Strait into the Chukchi and Beaufort Seas. We conclude that the long-term model results for the northern Bering Sea provide important insights into the ocean circulation and fluxes and they are a useful frame of reference for limited observations that are short-term and/or cover only a small geographic region.  相似文献   

15.
Phytoplankton pigments and size-fractionated biomass in the Chukchi and Beaufort Seas showed spatial and temporal variation during the spring and summer of 2002. Cluster analysis of pigment ratios revealed different assemblages over the shelf, slope and basin regions. In spring, phytoplankton with particle sizes greater than 5 μm, identified as diatoms and/or haptophytes, dominated over the shelf. Smaller (<5 μm) phytoplankton containing chlorophyll b, most likely prasinophytes, were more abundant over the slope and basin. Due to extensive ice cover at this time, phytoplankton experienced low irradiance, but nutrients were near maximal for the year. By summer, small prasinophytes and larger haptophytes and diatoms co-dominated in near-surface assemblages in largely ice-free waters when nitrate was mostly depleted. Deeper in the water column at 1–15% of the surface irradiance larger sized diatoms were still abundant in the upper nutricline. Phytoplankton from the shelf appeared to be advected through Barrow Canyon to the adjacent basin, explaining similar composition between the two areas in spring and summer. Off-shelf advection was much less pronounced for other slope and basin areas, which are influenced by the low-nutrient Beaufort gyre circulation, leading to a dominance of smaller prasinophytes and chlorophytes. The correlation of large-sized fucoxanthin containing phytoplankton with the higher primary production measurements shows promise for trophic status to be estimated using accessory pigment ratios.  相似文献   

16.
A quasi-two dimensional model of the carbon and nitrogen cycling above the 70m isobath of the southeastern Bering Sea at 57°N replicates the observed seasonal cycles of nitrate, ammonium, ΣCO2, pCO2, light penetration, chlorophyll, phytoplankton growth rate, and primary production, as constrained by changes in wind, incident radiation, temperature, ice cover, vertical and lateral mixing, grazing stress, benthic processing of phytodetritus and zooplankton fecal pellets, and the pelagic microbial loop of DOC, bacteria, and their predators. About half of the seasonal resupply of nitrate stocks to their initial winter conditions is derived from in situ nitrification, with the rest obtained from deep-sea influxes. Under the present conditions of atmospheric forcing, shelf-break exchange, and food web structure, this shelf ecosystem serves as a sink for atmospheric CO2, with storage in the forms of exported DOC, DIC, and unutilized POC (phytoplankton, bacteria, and fecal pellets).As a consequence of just the rising levels of atmospheric pCO2 since the the Industrial Revolution, however, the biophysical CO2 status of the Southeastern Bering Sea shelf may have switched over the last 250 years, from a prior source to the present sink, since this relatively pristine ecosystem has unergone little eutrophication. Such fluctuations of CO2 status may thus be reversed by the physical processes of : (1) reduction of atmospheric pCO2, (2) increased on welling of deep-sea ΣCO2, and (3) warming of shelf waters. Based on our application of this model to the Chukchi Sea and the Gulf of Mexico, about 1.0–1.2 gigatons C y-1 of atmospheric CO2 may now be sequestered by temperate and polar shelf ecosystems. When tropical systems are included, however, a positive net sink of only 0.6–0.8. × 1015g C y−1 may prevail over all shelves.  相似文献   

17.
The nearshore shelf of the Beaufort Sea is defined by extreme physical and biological gradients that have a distinctive influence on its productivity and trophic structure. Massive freshwater discharge from the Mackenzie River, along with numerous smaller rivers and streams elsewhere along the coast, produce an environment that is decidedly estuarine in character, especially in late spring and summer. Consequently, the Beaufort coast provides a critical habitat for several species of amphidromous fishes, some of which are essential to the subsistence lifestyle of arctic native populations. Because of its low in situ productivity, allochthonous inputs of organic carbon, identifiable on the basis of isotopic composition, are important to the functioning of this arctic estuarine system. Coastal erosion and river discharge are largely responsible for introducing high concentrations of suspended sediment from upland regions into the nearshore zone. The depletion in the 13C content of invertebrate and vertebrate consumers, which drops about 4–5‰ eastward along the eastern Alaskan Beaufort Sea coast, may reflect the assimilation of this terrestrial organic matter into local food webs. In addition, the large range in 13C values of fauna collected in the eastern Beaufort (nearly 8‰) compared to the same species in the northeastern Chukchi (3‰), indicate a lower efficiency of carbon transfer between trophic levels in the eastern Beaufort. The wider spread in stable isotope values in the eastern Beaufort may also reflect a decoupling between benthic and pelagic components. Isotopic tracer studies of amphidromous fishes in the Simpson Island barrier island lagoon revealed that terrestrial (peat) carbon may contribute as much as 30–50% of their total dietary requirements. On the eastern Alaska Beaufort Sea coast, the δ13C values of arctic cod collected in semi-enclosed lagoons were more depleted, by 3–4‰, compared to fish collected in the coastal Beaufort Sea. Calculations from isotopic mixing equations indicate cod from lagoons may derive 70% of their carbon from terrestrial sources. The δ15N values of lagoon fish were also 4‰ lower than coastal specimens, reflective of the lower δ15N values of terrestrially derived nitrogen (0–1.5‰ compared to 5–7‰ for phytoplankton). The role of terrestrial carbon in arctic estuarine food webs is especially important in view of the current warming trend in the arctic environment and the role of advective processes that transport carbon along the nearshore shelf. Biogeochemical studies of the arctic coastal estuarine environment may provide more insights into the function of these biologically complex ecosystems.  相似文献   

18.
Nutrient budgets for the South China Sea basin   总被引：3，自引：0，他引：3  
Varying atmospheric forcing and an elaborate geography make for a complex flow in the South China Sea (SCS). Throughout the year, the surface waters of the Kuroshio flow into the SCS, while the surface waters of the SCS flow out through the Bashi Channel. Cumulatively, there is a small (1 Sv) net outflow of surface water (0–350-m depth) from the SCS in the wet season, but a net inflow (3 Sv) in the dry season through the Bashi Channel. The differences are mainly made up by inflow and outflow of Sunda Shelf Water in the wet and dry seasons, respectively.Seawater, phosphorus, nitrogen and silicate budgets were calculated based on a box model. The results point out an intermediate water outflow (350–1350-m depth) into the West Philippine Sea (WPS) through the Bashi Channel in both the wet and dry seasons, though this, along with the nutrients it carries, is slightly larger in the dry season (2 Sv) than in the wet (1.8 Sv). More importantly, the export of nutrient-laden SCS intermediate water through the Bashi Channel subsequently upwells onto the East China Sea (ECS) shelf. The denitrification rate for shelves in the SCS is 0.11 mol N m−2 year−1, calculated by balancing the nitrogen budget. The oxygen consumption and the nutrient regeneration rates, based on the mass-balance and the one-dimensional advection–diffusion models, stand between those for the Bering Sea and the Sea of Japan.  相似文献   

19.
During three icebreaker cruises in the Arctic Ocean under different sea-ice conditions in 2002, undisturbed benthic surface sediments were collected and assayed for the presence of a short-lived (t1/2=53 d), particle-reactive cosmogenic radionuclide, 7Be, that is solely derived from atmospheric deposition. Under largely ice-covered conditions in May–June 2002, we did not detect this radionuclide in benthic surface sediments, despite significant inventories present in ice-rafted snow on the overlying sea ice (mean=86.8 Bq m−2±32.0 SD; n=9). During the July–August 2002 Shelf–Basin Interactions (SBI) cruise aboard the USCGC Healy and during a simultaneous cruise of the CCGS Sir Wilfrid Laurier on the Bering and Chukchi Shelf, which occupied the same general region following retreat and dissolution of Arctic ice cover, the 7Be present in this snow as well as surface deposition on to the sea ice-free water surface was detected in many benthic surface sediments, including some as deep as 945 m in Barrow Canyon. Inventories of 7Be in sediments were as high (60 Bq m−2) as the entire decay-corrected inventory present earlier in some snow samples collected on the sea-ice cover. Other deposition indicators such as the inventories of sediment chlorophyll, sediment oxygen respiration rates and 234Th-derived export fluxes also showed post-ice melt particle deposition and vertical transport, but in most cases the 7Be deposition was not tightly correlated with these other indicators, suggesting that 7Be sedimentation may not be controlled by the same processes. Our observations indicate that materials in sea ice, including contaminants, particulate organic, and mineral matter originating from atmospheric deposition or entrained in continental shelf sediments and rafted onto sea ice, can be rapidly transported to depth. The re-distribution of these materials as sea-ice drifts and eventually melts has the potential for impacting Arctic Ocean biogeochemical cycles and contaminant concentrations in areas of the Arctic remote from the original point of deposition.  相似文献   

20.
The distribution of chlorophyll a(Chl a) and its relationships with physical and chemical parameters in different regions of the Bering Sea were discussed in July 2010. The results showed the seawater column Chl a concentrations were 13.41–553.89 mg/m2 and the average value was 118.15 mg/m2 in the study areas. The horizontal distribution of Chl a varied remarkably from basin to shelf in the Bering Sea. The regional order of Chl a concentrations from low to high was basin, slope, outer shelf, inner shelf, and middle shelf. The vertical distribution of Chl a was grouped mainly from single-peak type in basin, slope, outer shelf, and middle shelf, where the deep Chl a maxima(DCM) layer was observed at 25–50 m, 30–35 m, 36–44 m, and 37–47 m, respectively. The vertical distribution of Chl a mainly had three basic patterns: standard single-peak type, surface maximum type, and bottom maximum type in the inner shelf. The analysis also showed that the transportation of ocean currents may control the distribution of Chl a, and the effects were not simple in the basin of the Bering Sea. There was a positive correlation between Chl a and temperature, but no significant correlation between Chl a and nutrients. The Bering Sea slope was an area deeply influenced by slope current. Silicate was the factor that controlled the distribution of Chl a within parts of the water in the slope. Light intensity was an important environmental factor in controlling seawater column Chl a in the shelf, where Chl a was limited by nitrate rather than phosphate within the upper water. Meanwhile, there was a positive relationship between Chl a and salinity. Algal blooms broke out at Sta. B6 of the southwestern St. Lawrence Island and Stas F6 and F11 in the middle of the Bering Strait.  相似文献   

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