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1.
We examined the interannual variability of Pacific Winter Water (PWW), both upstream in the northeastern Chukchi Sea and Barrow Canyon using mooring observations from 2000 to 2006, and downstream in the Canada Basin using hydrographic data acquired in 2002–2006. The interannual variation of PWW salinity is governed by two factors: (1) variability in the salinity of Pacific Water that flows northward through Bering Strait in winter; and (2) the input of salt associated with sea ice formation during winter in an intermittent coastal polynya located along the Alaskan coast between Cape Lisburne and Point Barrow. During the winters of 2000/2001 and 2001/2002 an increased transport of cold and saline PWW (S?>?33.5) to the basin via Barrow Canyon was observed. In 2000/2001 enhanced ice formation in the polynya contributed to the increased salinity of PWW, whereas in 2001/2002 the salinity of water entering through the Bering Strait was higher, and this resulted in more saline PWW being delivered to the basin. In the following four winters (2002/2003, 2003/2004, 2004/2005 and 2005/2006) the transport of cold and saline PWW in winter to the basin was less than that in the two preceding winters. In three of these four winters (2003/2004 being the exception) the coastal polynya was less active, thus reducing the input of salt due to brine enrichment. In the winter of 2003/2004, however, warmer water within the polynya region constrained ice formation and thus less cold and saline PWW was produced, despite the fact that the coastal polynya was active and frequently open.  相似文献   

2.
To assess the magnitude, distribution and fate of net community production (NCP) in the Chukchi Sea, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), and particulate organic carbon (POC) and particulate organic nitrogen (PON) were measured during the spring and summer of 2004 and compared to similar observations taken in 2002. Distinctive differences in hydrographic conditions were observed between these two years, allowing us to consider several factors that could impact NCP and carbon cycling in both the Chukchi Shelf and the adjacent Canada Basin. Between the spring and summer cruises high rates of phytoplankton production over the Chukchi shelf resulted in a significant drawdown of DIC in the mixed layer and the associated production of DOC/N and POC/N. As in 2002, the highest rates of NCP occurred over the northeastern part of the Chukchi shelf near the head of Barrow Canyon, which has historically been a hotspot for biological activity in the region. However, in 2004, rates of NCP over most of the northeastern shelf were similar and in some cases higher than rates observed in 2002. This was unexpected due to a greater influence of low-nutrient waters from the Alaskan Coastal Current in 2004, which should have suppressed rates of NCP compared to 2002. Between spring and summer of 2004, normalized concentrations of DIC in the mixed layer decreased by as much as 280 μmol kg−1, while DOC and DON increased by ∼16 and 9 μmol kg−1, respectively. Given the decreased availability of inorganic nutrients in 2004, rates of NCP could be attributed to increased light penetration, which may have allowed phytoplankton to increase utilization of nutrients deeper in the water column. In addition, there was a rapid and extensive retreat of the ice cover in summer 2004 with warmer temperatures in the mixed layer that could have enhanced NCP. Estimates of NCP near the head of Barrow Canyon in 2004 were ∼1500 mg carbon (C) m−2 d−1 which was ∼400 mg C m−2 d−1 higher than the same location in 2002. Estimates of NCP over the shelf-break and deep Canada Basin were low in both years, confirming that there is little primary production in the interior of the western Arctic Ocean due to near-zero concentrations of inorganic nitrate in the mixed layer.  相似文献   

3.
The Western Arctic Shelf–Basin Interactions (SBI) project is a 10-year Arctic environmental change program. A major field campaign occurred in the spring, summer and fall seasons between 2002 and 2004. The SBI program was developed to investigate the production, transformation and fate of carbon on shelf and slope regions of the Chukchi and Beaufort seas and shelf–basin interactions with the Arctic Basin. This 2nd special issue documents many of the key findings, ranging from sea ice and hydrographic changes to water column and sediment dynamics and trophic level interactions during the core Phase II field program. The integration of these results with ongoing synthesis and modeling activities within the SBI program are illustrating the critical importance of this continental shelf environment to understand shelf–basin interactions and the ongoing changes being observed and forecasted in the marine Amerasian Arctic.  相似文献   

4.
Hydrographic conditions during the 2002 SBI process experiments   总被引：3，自引：0，他引：3  
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5.
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   

6.
The Arctic Oscillation (AO) has important effects on the sea ice change in terms of the dynamic and thermodynamic processes. However, while the dynamic processes of AO have been widely explored, the thermodynamic processes of AO need to be further discussed. In this paper, we use the fifth state-of-the-art reanalysis at European Centre for Medium-Range Weather Forecasts (ERA5) from 1979 to 2020 to investigate the relationship between AO and the surface springtime longwave (LW) cloud radiative forcing (CRF), summertime shortwave (SW) CRF in the Arctic region (65°?90°N). In addition, the contribution of CRF induced by AO to the sea ice change is also discussed. Results indicate that the positive (negative) anomalies of springtime LW CRF and summertime SW CRF are generally detected over the Arctic Ocean during the enhanced positive (negative) AO phase in spring and summer, respectively. Meanwhile, while the LW (SW) CRF generally has a positive correlation with AO index (AOI) in spring (summer) over the entire Arctic Ocean, this correlation is statistically significant over 70°?85°N and 120°W?90°E (i.e., region of interest (ROI)) in both seasons. Moreover, the response of CRF to the atmospheric conditions varies in spring and summer. We also find that the positive springtime (summertime) AOI tends to decrease (increase) the sea ice in September, and this phenomenon is especially prominent over the ROI. The sensitivity study among sea ice extent, CRF and AOI further reveals that decreases (increases) in September sea ice over the ROI are partly attributed to the springtime LW (summertime SW) CRF during the positive AOI. The present study provides a new pattern of AO affecting sea ice change via cloud radiative effects, which might benefit the sea ice forecast improvement.  相似文献   

7.
To address the mechanisms controlling halocline variability in the Beaufort Sea, the relationship between halocline shoaling/deepening and surface wind fields on seasonal to decadal timescales was investigated in a numerical experiment. Results from a pan-Arctic coupled sea ice-ocean model demonstrate reasonable performances for interannual and decadal variations in summer sea ice extent in the entire Arctic and in freshwater content in the Canada Basin. Shelf-basin interaction associated with Pacific summer and winter transport depends on basin-scale wind patterns and can have a significant influence on halocline variability in the southern Beaufort Sea. The eastward transport of fresh Pacific summer water along the northern Alaskan coast and Ekman downwelling north of the shelf break are commonly enhanced by cyclonic wind in the Canada Basin. On the other hand, basin-wide anti-cyclonic wind induces Ekman upwelling and blocks the eastward current in the Beaufort shelf-break region. Halocline shoaling/deepening due to shelf-water transport and surface Ekman forcing consequently occur in the same direction. North of the Barrow Canyon mouth, the springtime down-canyon transport of Pacific winter water, which forms by sea ice production in the Alaskan coastal polynya, thickens the halocline layer. The model result indicates that the penetration of Pacific winter water prevents the local upwelling of underlying basin water to the surface layer, especially in basin-scale anti-cyclonic wind periods.  相似文献   

8.
The response of phytoplankton to the Beaufort shelf-break eddies in the western Arctic Ocean is examined using the eddy-resolving coupled sea ice–ocean model including a lower-trophic marine ecosystem formulation. The regional model driven by the reanalysis 2003 atmospheric forcing from March to November captures the major spatial and temporal features of phytoplankton bloom following summertime sea ice retreat in the shallow Chukchi shelf and Barrow Canyon. The shelf-break warm eddies spawned north of the Barrow Canyon initially transport the Chukchi shelf water with high primary productivity toward the Canada Basin interior. In the eddy-developing period, the anti-cyclonic rotational flow along the outer edge of each eddy moving offshore occasionally traps the shelf water. The primary production inside the warm eddies is maintained by internal dynamics in the eddy-maturity period. In particular, the surface central area of an anti-cyclonic eddy acquires adequate light, nutrient, and warm environment for photosynthetic activity partly attributed to turbulent mixing with underlying nutrient-rich water. The simulated biogeochemical properties with the dominance of small-size phytoplankton inside the warm eddies are consistent with the observational findings in the western Arctic Ocean. It is also suggested that the light limitation before autumn sea ice freezing shuts down the primary production in the shelf-break eddies in spite of nutrient recovery. These results indicate that the time lag between the phytoplankton bloom in the shelf region following the summertime sea ice retreat and the eddy generation along the Beaufort shelf break is an important index to determine biological regimes in the Canada Basin.  相似文献   

9.
Within larger ice-free regions of the western Arctic Seas, subject to ongoing trophic cascades induced by past overfishing, as well as to possible future eutrophication of the drainage basins of the Yukon and Mackenzie Rivers, prior very toxic harmful algal blooms (HABs) – first associated with ∼100 human deaths near Sitka, Alaska in 1799 – may soon expand. Blooms of calcareous coccolithophores in the Bering Sea during 1997–1998 were non-toxic harbingers of the subsequent increments of other non-siliceous phytoplankton. But, now saxitoxic dinoflagellates, e.g. Alexandrium tamarense, were instead found by us within the adjacent downstream Chukchi Sea during SBI cruises of 2002 and 2003. A previous complex, coupled biophysical model had been validated earlier by ship-board observations from the Chukchi/Beaufort Seas during the summer of 2002. With inclusion of phosphorus as another chemical state variable to modulate additional competition by recently observed nitrogen-fixers, we now explore here the possible consequences of altered composition of dominant phytoplankton functional groups [diatoms, microflagellates, prymnesiophyte Phaeocystis colonies, coccolithophores, diazotrophs, and dinoflagellates] in relation to increases of the toxic A. tamarense, responding to relaxation of grazing pressure by herbivores north of Bering Strait as part of a continuing trophic cascade. Model formulation was guided by validation observations obtained during 2002–2004 from: cruises of the SBI, CHINARE, and CASES programs; moored arrays in Bering Strait; other RUSALCA cruises around Wrangel Island; and SBI helicopter surveys of the shelf-break regions of the Arctic basin. Our year-long model scenarios during 2002–2003 indicate that post bloom silica-limitation of diatoms, after smaller simulated spring grazing losses, led to subsequent competitive advantages in summer for the coccolithophores, dinoflagellates, and diazotrophs. Immediate top-down control is exerted by imposed grazing pressures of the model’s herbivores and bottom-up control is also effected by light-, nitrate-, ammonium-, silicate-, and phosphate-modulated competition among the six functional groups of the simulated phytoplankton community. Similar to the history of the southern North Sea adjacent to the Rhine River, possible farming of northwestern Alaska and Canada, in conjunction with other human activities of ice retreat and overfishing, may lead to future exacerbations of poisonous phytoplankton. These potential killers include both toxic dinoflagellate and diazotroph HABs, deadly to terrestrial and marine mammals, as well as those of prymnesiophytes, some of which have already foamed beaches, while others have killed fishes of European waters.  相似文献   

10.
1Introduction Besidestheprecipitationandriverdischarges,the watersinthePacificOceanandtheAtlanticOceanare thesourcesoftheArcticOceanwater.TheAtlantic waterenterstheArcticOceanviatheFramStraitand theBarentsSea.Foritsdenserfeatureduetohigh salinity,mostofitsinkstothenorthofSvaldbardand circulatesinallthedeepbasinsintheArcticOcean, formingthedeepandbottomwatersoftheArcticO- cean(Aagaardetal.,1985;Rudelsetal.,1999).The BeringStraitistheonlychannelforthePacificwater toflowintotheArcticOce…  相似文献   

11.
Understanding the physical and biogeochemical processes that control the exchange of biogenic carbon within and between the arctic shelves, slopes, and deep basins is a key objective of the Western Arctic Shelf-Basin Interaction program (SBI). Here, egg production (EP) of the dominant copepod Calanus glacialis/marshallae was used as an indicator of food limitation for the mesozooplankton community in the Chukchi and Beaufort Seas in spring and summer, 2002. Both C. glacialis and C. marshallae may occur in this region but the two cannot easily be differentiated visually. Four oceanographic regions were objectively identified that roughly corresponded to the different pathways in circulation of nutrient-rich Pacific water. A ‘transition’ region characterized by ‘older’ Pacific water was located at the shelfbreak and separated the nutrient-rich shelf water and the low-nutrient waters of the deep basin. The observed spatial pattern in EP in C. glacialis/marshallae in spring and summer resulted both from the different water mass environments and from the reproductive cycle of the species. EP was greater on the shelf than in the basin, corresponding to differences in body size and nitrogen condition factor (NCF) in females, while the egg viability was generally high throughout the study area. EP showed no relationship with low-chlorophyll a biomass under heavy ice-cover in spring, while a significant relationship was observed in the more open water in summer. Adult female carbon condition factor (CCF) was much higher in summer, reflecting the accumulation of lipids during the growth season. Small animals with a markedly greater NCF dominated on the shelf. The shelfbreak region contained a mixture of females from the shelf and the basin with intermediate sizes, conditions, and EP rates. The occurrence of water typical of the ‘transition’ shelfbreak region and elevated EP in C. glacialis/marshallae offshore on the Barrow Canyon and East Barrow sections indicated offshore transport of productive shelf water and the associated plankton community. The input of nutrient-rich Pacific water and accompanying elevated production to the northern Chukchi Sea and the Chukchi-Beaufort shelfbreak region may contribute to the reproductive success of C. glacialis/marshallae in this region.  相似文献   

12.
Exopolymeric substances (EPS) produced by microorganisms play important roles in various aquatic, porous, and extreme environments. Only recently has their occurrence in sea ice been considered. We used macroscopic and microscopic approaches to study the content and possible ecological role of EPS in wintertime fast ice near Barrow, Alaska (71°20′ N, 156°40′ W). Using Alcian blue staining of melted ice samples, we observed high concentrations of EPS in all samples examined, ranging from 0.79 to 7.71 mg xanthan gum equivalents (XGEQV) l−1. Areal conversions to carbon equivalents yielded 1.5−1.9 g C m−2 ice in March and 3.3−4.0 g C m−2 in May (when the ice was thicker). Although EPS did not correlate with macronutrient or pigment data, the latter analyses indicated ongoing or recent biological activity in the ice within temperature horizons of −11°C to −9°C and warmer. EPS correlated positively with bacterial abundance (although no functional relationship could be deduced) and with dissolved organic carbon (DOC) concentrations. Ratios of EPS/DOC decreased at colder temperatures within the core, arguing against physical conversion of DOC to EPS during freezing. When sea-ice segments were maintained at representative winter temperatures (−5°C,−15°C and −25°C) for 3−14 months, the total EPS content increased significantly at rates of 5−47 μg XGEQV l−1 d−1, similar to published rates of EPS production by diatoms. Microscopic images of ice-core sections at these very cold temperatures, using a recently developed non-invasive method, revealed diatoms sequestered in spacious brine pockets, intact autofluorescent chloroplasts in 47% of the (pennate) diatoms observed, and indications of mucus in diatom-containing pores. The high concentrations of EPS detected in these winter ice cores represent a previously unrecognized form of organic matter that may contribute significantly to polar ocean carbon cycles, not only within the ice but after springtime release into the water column. The EPS present in very high concentrations in the brine of these microhabitats appear to play important buffering and cryoprotectant roles for microorganisms, especially diatoms, against harsh winter conditions of high salinity and potential ice-crystal damage.  相似文献   

13.
The diffuse attenuation coefficient(Kd) for downwelling irradiance is calculated from solar irradiance data measured in the Arctic Ocean during 3rd and 4th Chinese National Arctic Research Expedition(CHINARE), including 18 stations and nine stations selected for irradiance profiles in sea water respectively. In this study, the variation of attenuation coefficient in the Arctic Ocean was studied, and the following results were obtained. First, the relationship between attenuation coefficient and chlorophyll concentration in the Arctic Ocean has the form of a power function. The best fit is at 443 nm, and its determination coefficient is more than 0.7. With increasing wavelength, the determination coefficient decreases abruptly. At 550 nm, it even reaches a value lower than 0.2. However, the exponent fitted is only half of that adapted in low-latitude ocean because of the lower chlorophyll-specific absorption in the Arctic Ocean. The upshot was that, in the case of the same chlorophyll concentration, the attenuation caused by phytoplankton chlorophyll in the Arctic Ocean is lower than in low-latitude ocean. Second, the spectral model, which exhibits the relationship of attenuation coefficients between 490 nm and other wavelength, was built and provided a new method to estimate the attenuation coefficient at other wavelength, if the attenuation coefficient at 490 nm was known. Third, the impact factors on attenuation coefficient, including sea ice and sea water mass, were discussed. The influence of sea ice on attenuation coefficient is indirect and is determined through the control of entering solar radiation. The linear relationship between averaging sea ice concentration(ASIC, from 158 Julian day to observation day) and the depth of maximum chlorophyll is fitted by a simple linear equation. In addition, the sea water mass, such as the ACW(Alaskan Coastal Water), directly affects the amount of chlorophyll through taking more nutrient, and results in the higher attenuation coefficient in the layer of 30–60 m. Consequently, the spectral model of diffuse attenuation coefficient, the relationship between attenuation coefficient and chlorophyll and the linear relationship between the ASIC and the depth of maximum chlorophyll, together provide probability for simulating the process of diffuse attenuation coefficient during summer in the Arctic Ocean.  相似文献   

14.
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   

15.
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   

16.
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   

17.
Measurements of sea-ice thickness were obtained from drill holes, an ice-based electromagnetic induction instrument (IEM), and a ship-borne electromagnetic induction instrument (SEM) during the early-melt season in the southern Chukchi Sea in 2002 and 2004, and in late summer 2003 at the time of minimum ice extent in the northern Chukchi Sea. An ice roughness criterion was applied to distinguish between level and rough or ridged ice. Ice-thickness modes in the probability density functions (PDFs) derived from drill-hole and IEM measurements agreed well, with modes at 1.5–1.6 and 1.8–1.9 m for all data from level ice. The PDFs derived from SEM measurements show that the primary modes are at 0.1 and 1.1 m in 2003 and 0.7 m in 2004. In 2002 and 2004, significant fractions (between one-third and one-half) of level ice were found to consist of rafted ice segments. Snow depth varied significantly between years, with 2004 data showing more than half the snow cover on level ice to be at or below 0.05 m depth in late spring. Ice growth simulations and examination of ice drift and deformation history indicate that impacts of atmospheric and oceanic warming on level-ice thickness in the region over the past few decades are masked to a large extent by variability in snow depth and the contribution of deformation processes. In comparison with submarine sonar ice-thickness data from previous decades, a reduction in ice thickness by about 0.5–1 m is in part explained by the replacement of multi-year with first-year ice over the Chukchi and Beaufort shelves.  相似文献   

18.
The study establishes an annual estimate for annual primary production of 81 g C m−2 for the open Greenland Sea based on data from five cruises and literature data. This estimate agrees well with a model estimate based on nutrient utilisation but is a factor of 2–5 less than published primary production estimates made by remote sensing of this area. The seasonal distribution of particulate primary production in open Greenland Sea waters followed the seasonal distribution of surface irradiance with a peak in June, indicating that light is the primary factor governing primary production in the area. At stations along the ice edge, blooms were recorded in both June and August, suggesting a pattern of repeated blooms during the summer season at the ice edge. Subsurface phytoplankton peaks were a persistent feature in the open Greenland Sea from May to August. These peaks were consisted of actively photosynthesising phytoplankton and up to 90% of total water column particulate primary production was estimated to occur in association with these peaks. Diatoms dominated the phytoplankton community during the spring bloom and in the Polar Water during August. Size distribution analyses of the phytoplankton communities indicated that the relative abundance of large cells compared to small cells was greatest in May as compared to June and August. No significant differences were noted between June and August in the slope of the phytoplankton size distribution spectra. Inorganic nitrogen and phosphorus nutrients were measurable in surface waters on all cruises. Only in August were there some indications (altered Redfield ratios and higher nutrient concentrations in subsurface chlorophyll peaks than at the surface) of nutrient depletion of surface waters. Implications for food web structure and carbon flux of these patterns in phytoplankton activity and distribution are discussed.  相似文献   

19.
As part of the Western Arctic Shelf–Basin Interactions (SBI) project, the production and fate of organic carbon and nitrogen from the Chukchi and Beaufort Sea shelves were investigated during spring (5 May–15 June) and summer (15 July–25 August) cruises in 2002. Seasonal observations of suspended particulate organic carbon (POC) and nitrogen (PON) and large-particle (>53 μm) size class suggest that there was a large accumulation of carbon (C) and nitrogen (N) between spring and summer in the surface mixed layer due to high phytoplankton productivity. Considerable organic matter appeared to be transported from the shelf into the Arctic Ocean basin in an elevated POC and PON layer at the top of the upper halocline. Seasonal changes in the molar carbon:nitrogen (C:N) ratio of the suspended particulate organic matter (POM) pool reflect a change in the quality of the organic material that was present and presumably being exported to the sediment and to Arctic Ocean waters adjacent to the Chukchi and Beaufort Sea shelves. In spring, low particulate C:N ratios (<6; i.e., N rich) were observed in nitrate-replete surface waters. By the summer, localized high particulate C:N ratios (>9; i.e., N-poor) were observed in nitrate-depleted surface waters. Low POC and inorganic nutrient concentrations observed in the surface layer suggest that rates of primary, new and export production are low in the Canada Basin region of the Arctic Ocean.  相似文献   

20.
Size-fractionated primary productivity and chlorophylla concentration were studied at two stations in the temperate neritic water of Funka Bay, Japan, from April 1984 to May 1985. Size distributions of phytoplankton were discussed in relation to nutrient availability. In the central part of the bay, 66% of the annual primary production occurred during the spring phytoplankton bloom with 95% of the spring production being accounted for by the greater than 10µm size fraction, which was dominated by diatoms. The increase in this large fraction was enhanced at both stations when nutrient concentrations increased in the bay's upper layer. Under low nutrient concentrations during summer, small phytoplankters (<2µm) accounted for 40 to 75% (average 60%) of the total14C uptake at the central station, and from 25 to 59% (average, 45%) at the coastal station. However, a sudden nutrient enrichment at the coastal station during the summer triggered the growth of the large size fraction. These seasonal and regional changes in total14C uptake were attributed to the large size fraction, composed mainly of diatoms. From the decreases in various nutrients during diatom blooms, it was further suggested that the predominance of diatoms was determined, not only by nutrient concentrations, but also by their relative availability.Contribution No. 205 from the Research Institute of North Pacific Fisheries, Faculty of Fisheries, Hokkaido University.  相似文献   

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