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1.
Factors controlling the timing of major (>10 mg chlorophyll a m−3) spring bloom events in the estuarine waters of the Solent, on the south coast of the UK, have been investigated. Winter to summer variations in chlorophyll a concentration together with relevant meteorological and hydrographical data have been analysed for 5 years (1988, 1992, 2001, 2002 and 2003). Mean water column irradiance is demonstrated to be the main factor controlling the timing of the first major spring bloom event, usually dominated by large chain-forming diatoms. When chlorophyll a concentration first exceeds 10 mg m−3 in spring (usually in May) the mean water column photosynthetic active radiation (PAR) averaged for one week prior to the sampling date was always >380 W h m−2 d−1. Prior to the main spring bloom event surface incident radiation and water turbidity combine to limit chlorophyll a concentration to levels <10 mg m−3. Chlorophyll a concentrations >10 mg m−3 do not occur in the Solent until almost the entire 10 m water column is within the euphotic zone (i.e. above 1% light level) and light extinction coefficient (k) is ca. ≤0.5 m−1. Statistically, river flow explains the largest percentage of the variations in k and the delayed bloom in June 2002 is due to increased cloud cover and high levels of rainfall in May, which caused a reduction in surface incident irradiance and increased turbidity. Chlorophyll a peaks during these major bloom events generally occur on spring tides when increased mixing rates favour net growth of diatoms.  相似文献   

2.
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   

3.
Egg production of Calanus finmarchicus was studied during joint basin-scale surveys in April–June 2003 in the Norwegian Sea. Surveys covered the whole Norwegian Sea and were conducted from Norwegian, Icelandic and Faroese research vessels. Stations were classified as being in pre-bloom, bloom or post-bloom phase according to levels of chlorophyll a and nitrate. Individual egg production rates and population egg production rates were calculated and compared between areas. Both individual egg production rates (eggs female−1 day−1) and population egg production rates (eggs m−2 day−1) were significantly higher in bloom areas compared with pre-bloom and post-bloom areas. However, when integrated over an estimated duration of the three phases, the time-integrated egg production (eggs m−2) in most years was highest in the pre-bloom phase, and this was explained by the longer duration of this phase compared with the two other phases.  相似文献   

4.
In March and September 1995, bacterial production was measured by the 3H-leucine method in the oligotrophic Cretan Sea (Aegean Sea, Eastern Mediterranean) in the framework of the CINCS/MTP program. Samples were obtained from four stations (a coastal, a continental shelf and 2 open-sea stations) for the construction of vertical profiles of bacterial abundance and production. Bacterial production ranged from 0.1 μg C m−3 h−1 at 1500 m depth, to 82 μg C m−3 h−1 in March at 50 m at the coastal station. Higher bacterial integrated production was observed in March at the coastal station (131 mg C m−2 d−1 for the 0–100 m layer). Bacterial production, integrated through the water-column, was similar in March and September for the open-sea stations (60–70 mg C m−2 d−1). Relative to production, bacterial concentrations varied little between stations and seasons ranging from 9×105 ml−1 to 3×105 ml−1. Relationships between bacterial biomass and bacterial production indicated seasonal differences, likely reflecting resource limitation of bacterial biomass in March (bloom situation), and predator limitation of bacterial biomass in September (post-bloom situation).  相似文献   

5.
Cylindrical sediment traps were deployed at various depths in the anoxic water of Framvaren for two periods of one year (1981–1982 and 1983–1984). The traps were emptied three times during 1981–1982 and five times during 1983–1984. The vertical fluxes of total suspended material, organic carbon and nitrogen were calculated on a daily and annual basis. The average annual sediment flux 20 m above the bottom was approximately 60 g m−2 y−1 and the flux of organic carbon was 20 g m−2 y−1. On the basis of an average C/N ratio of 8 and a constant carbon flux below a depth of 20 m, it is concluded that little mineralization of the organic matter takes place in the anoxic water column. Assuming a primary production of the order to 50–100 g m−2 y−1, 22–24% of that reaches the anoxic water masses. Further breakdown of organic matter takes place in the surface sediments.  相似文献   

6.
The Ross Sea, a region of high seasonal production in the Southern Ocean, is characterized by blooms of the haptophyte Phaeocystis antarctica and of diatoms. The different morphology, structural composition and consumption of these two phytoplankton by grazing zooplankton may result in different carbon cycling dynamics and carbon flux from the euphotic zone. We sampled short-term (2 days) particle flux at 5 sites from 177.6°W to 165°E along a transect at 76.5°S with traps placed below the euphotic zone at 200 m during December 1995–January 1996. We estimated carbon flux of as many eucaryotic organisms and fecal pellets as possible using microscopy for counts and measurements and applying volume:carbon conversions from the literature. Eucaryotic organisms contributed about 20–40% of the total organic carbon flux in both the central Ross Sea polynya and in the western polynya, and groups of organisms differed in contribution to the carbon flux at the different sites. Algal carbon flux ranged from 4.5 to 21.1 mg C m−2 day−1 and consisted primarily of P. antarctica (cell plus mucus) and diatom carbon at all sites. Different diatom species dominated the diatom flux at different sites. Carbon fluxes of small pennate diatoms may have been enhanced by scavenging, by sinking senescent P. antarctica colonies. Heterotrophic carbon flux ranged from 9.2 to 37.6 mg C m−2 day−1 and was dominated by athecate heterotrophic dinoflagellate carbon in general and by carbon flux of a particular large athecate dinoflagellate at two sites. Fecal pellet carbon flux ranged from 4.6 to 54.5 mg C m−2 day−1 and was dominated by carbon from ovoid/angular pellets at most sites. Analysis of fecal pellet contents suggested that large protozoans identified by light microscopy contributed to ovoid/angular fecal pellet fluxes. Carbon flux as a percentage of daily primary production was lowest at sites where P. antarctica predominated in the water column and was highest at sites where fecal pellet flux was highest. This indicates the importance of grazers in carbon export.  相似文献   

7.
Concentrations and sinking rates of particulate biogenic silica (BSi), chlorophyll a (chl a) and phaeopigments (phae) (< 3 μm, 3–10 μm, > 10 μm and total), as well as the abundances of the major phytoplankton species, were studied during September 1991 in the Eastern Laptev Sea and the lower Lena River (Siberian Arctic). The highest chl a concentrations were found in two major “new” production regimes of the study area: (1) a deep chl a maximum (5.8 mg chl a m−3) (formed by the diatom Chaetoceros socialis) at 30 m depth on the outer shelf of the northern Laptev Sea, and (2) in the Lena River, where the phytoplankton community was dominated by fresh water diatoms (1.5 to 4.5 mg chl a m−3). Elevated chl a concentrations were also found in the river plume phytoplankton community (dominated by brackish water diatoms), NE of the Lena delta. In the Laptev Sea, the low chl a (0.1 to 3 mg chl a m−3) and high phae concentrations (0.5 to 14 mg phae m−3) indicated that the phytoplankton community (dominated by picoplanktic algae and nanoflagellates) was already senescent and affected by grazing losses. Biogenic silica values were highest in the Lena River (4 to 17 μM) as compared to the low values found in the Laptev Sea (0.3 to 4 μM). The large chl a size fraction, phae and BSi in the Lena River samples revealed the highest measured sinking rates (1.4, 2.3, and 1.5 m d−1, respectively). The formation of a strong halocline, decreasing turbulence, and possible nutrient deficiency resulted in death, disintegration and rapid sedimentation of fresh water diatoms. This was accompanied by a decrease in the BSi concentration and growth of the picoplanktic size fraction (< 3 μm) in the estuarine mixing zone (Gulf of Buorkhaya). Only a minor part of BSi was bound to intact diatom cells (< 3%) in the surface layer, most of which being apparently associated with detrital particles. In the Lena River, approximately 12% of the total silica was bound to BSi fraction, yet elsewhere in the Laptev Sea and in the estuarine mixing zone the BSi:total silica ratio was ≤ 5%. Thus, the results reflected the successional stage of a late summer phytoplankton community, characterized by dominance of small autotrophs and patchy distribution of senescent diatoms no longer able to affect the relative high levels of dissolved silica supplied by the Lena River.  相似文献   

8.
The Laptev Sea is a high-Arctic epicontinental sea north of Siberia (Russia) that is one of the least understood regions of the world’s ocean. It is characterized by a shallow and broad shelf plateau, high influx of river water, sediments and nutrients during summer, long-lasting sea-ice cover from October to May, and the formation of a narrow flaw-lead polynya off the fast-ice edge during winter.Here, we describe results of a German–Russian research project (1993-present), presenting the distribution patterns and dynamics of its marine flora and fauna, as well as pathways and processes of coupling between sea-ice, water-column and sea-floor biota.Three ecological zones are distinguished along a combined east–west and Lena-impact gradient, differing in the composition of pelagic and benthic communities. In general, high Chl a concentrations in the sediments indicate a tight coupling between sympagic and pelagic primary production and nutrient supply to the benthos throughout the entire Laptev Sea. However, there were pronounced regional differences between the ecological zones in magnitude of primary production and trophic dynamics. Primary production during the ice-free summer was highest in the estuarine zone most strongly influenced by the Lena River (210 mg C m−2 day−1). The western and northeastern Laptev Sea yielded 55 and 95 mg C m−2 day−1, respectively. Moreover, the zones differed in the partitioning of carbon flux between zooplankton and benthic food webs. In the Lena zone zooplankton carbon demand was about 31 mg C m−2 day−1 whereas in the western zone it was 21 mg C m−2 day−1 and in the eastern zone 4 mg C m−2 day−1. Total benthic carbon demand was 32 mg C m−2 day−1 for the Lena zone, 56 mg C m−2 day−1 in the western zone and 100 mg C m−2 day−1 in the northeastern zone.A carbon budget constructed for the Laptev Sea indicates that (1) a high proportion of primary production is channelled through the benthic trophic web, bypassing the pelagic trophic web, and (2) autochthonous primary production in the northeastern and western Laptev Sea might not be sufficient to fuel both pelagic and benthic secondary production and, hence, input of allochthonous organic carbon is required to balance the overall carbon demand.  相似文献   

9.
In January–February 2001, we measured microbial biomass as ATP and community respiration as ETS activity of organisms < 200 μm in the aphotic zone of the Ross Sea. Microbial respiration amounted to 2.14 mmol C m− 2 day− 1 in the depth range 200–1000 m. Our daily estimates of carbon export are close to the daily percentage of net community production (NCP), removed as sinking biogenic particles from the upper 100 m in the entire Ross Sea, but lower than those of other oceanic systems. Comparing remineralization determined in this study with that obtained by sediment traps in the Ross Sea, it appeared that about 63% of organic carbon remineralized by respiration derived from POC pool. Such evidence highlighted POC source as the main organic fuel of the biological pump in the Ross Sea.  相似文献   

10.
Seasonal change in the downward carbon transport due to respiration and mortality through diel vertical migration (DVM) of the calanoid copepods Metridia pacifica and Metridia okhotensis was estimated in the Oyashio region, western subarctic Pacific during six cruises from June 2001 to June 2002. M. pacifica (C4, C5 and adult females) was an active migratory species throughout the year though its DVM amplitude varied among seasons and stages. The mean distribution depths of adult females during the daytime were positively related with the illumination level in the water column, being shallowest in April and deepest in January. M. okhotensis generally showed less-extensive migrations than M. pacifica. Therefore, together with their lower abundance, this species is considered to be a less-important mechanism of downward transport of carbon except for April when their DVM was more active and descended deeper than M. pacifica, which remained in the upper 150 m even during the daytime. The mean migrating biomass of the two Metridia species was 558 mg C m−2 d−1 and was high during summer to winter (263–1676 mg C m−2 d−1) and low during spring (59–63 mg C m−2 d−1). Total downward flux through DVM fluctuated between 1.0 and 20.0 mg C m−2 d−1 with an annual mean of 8.0 mg C m−2 d−1. Contribution of the respiratory flux was greater than the mortality flux and accounted for 64–98% of total migratory flux throughout the year except for January when contribution of both fluxes was equal. Overall the annual carbon transport by DVM of Metridia spp. was estimated as 3.0 g C m−2 year−1, corresponding to 15% of the annual total POC flux at 150 m at the study site, suggesting that DVM is a significant process for carbon export in the subarctic region as well as that in tropical and subtropical oceanic regions. Since DVM in M. pacifica is more active during the non-bloom season when the gravitational flux of particulate matter is low, this species plays an important role in driving the biological pump in the subarctic Pacific during summer to winter.  相似文献   

11.
The geomorphic, oceanographic, terrestrial and anthropogenic attributes of the European coastal zone are described and published data on ecosystem function (primary production and respiration) are reviewed. Four regions are considered: the Baltic Sea, Mediterranean Sea, Black Sea and the European Atlantic coast including the North Sea. The metabolic database (194 papers) suffers from a non-homogeneous geographical coverage with no usable data for the Black Sea which was therefore excluded from this part of our study. Pelagic gross primary production in European open shelves is, by far, the most documented parameter with an estimated mean of 41 mmol C m−2 d−1, the lowest value is reported in the Mediterranean Sea (21 mmol C m−2 d−1) and the highest one in the Atlantic/North Sea area (51 mmol C m−2 d−1). Microphytobenthic primary production, mostly measured in shallow areas, is extrapolated to the entire 0–200 m depth range. Its contribution to total primary production is low in all regions (mean: 1.5 mmol C m−2 d−1). Although macrophyte beds are very productive, a regional production estimate is not provided in this study because their geographical distribution along the European coastline remains unknown. Measurements of pelagic community respiration are clearly too sparse, especially below the euphotic zone, to yield an accurate picture of the fate of organic matter produced in the water column. With a mean value of 17 mmol C m−2 d−1, benthic community respiration consumes approximately 40% of the pelagic organic matter production. Estuaries generally exhibit high metabolic rates and a large range of variation in all parameters, except microphytobenthic primary production. Finally, the problem of eutrophication in Europe is discussed and the metabolic data obtained in the framework of the Land–Ocean Interactions in the Coastal Zone (LOICZ) project are compared with available direct measurements of net ecosystem production.  相似文献   

12.
Accumulating evidence points to the importance of mesoscale eddies in supplying nutrients to surface waters in oligotrophic gyres. However, the nature of the biological response and its evolution over time has yet to be elucidated. Changes in mesozooplankton community composition due to eddy perturbation also could affect biogeochemical cycling. Over the course of two summers we sampled seven eddies in the Sargasso Sea. We focused on and followed a post-phytoplankton bloom cyclonic eddy (C1) in 2004 and a blooming mode-water anticyclonic eddy (A4) in 2005. We collected zooplankton in all eddies using a Multiple Opening and Closing Net Environmental Sampling System (MOCNESS) and quantified biomass (>0.15 mm, in five size fractions) from 0 to 700 m over nine discrete depth intervals. Zooplankton biomass (>0.5 mm) in the upper 150 m was similarly enhanced at night for the periphery of C1 and the center of A4 at 0.514 g m−2 and 0.533 g m−2, respectively, compared to outside (0.183 g m−2 outside C1 and 0.197 g m−2 outside A4). Despite minimal chlorophyll a enhancement and dominance by picoplankton in C1, zooplankton biomass increased most for the largest size class (>5 mm). Gut fluorescence for euphausiids and large copepods was also elevated on the C1 periphery. In A4, peak biomass occurred at eddy center coincident with peak primary production, but was highly variable (changing by >3-fold) over time, perhaps resulting from the dense, but patchy distribution of diatom chains in this region. Shifts in zooplankton community composition and abundance were reflected in enhancement of fecal pellet production and active transport by diel vertical migration in eddies. Inside C1 the flux of zooplankton fecal pellets at 150 m in June 2004 was 1.5-fold higher than outside the eddy, accounting for 9% of total particulate organic carbon (POC) flux. The flux of fecal pellets (mostly from copepods) increased through the summer in eddy A4, matching concurrent increases in zooplankton <2 mm in length, and accounting for up to 12% of total POC flux. Active carbon transport by vertically migrating zooplankton was 37% higher on the periphery of C1 and 74% higher at the center of A4 compared to the summer mean at the Bermuda Atlantic Time-series Study (BATS) station. Despite contrasting responses by the phytoplankton community to cyclonic and mode-water eddies, mesozooplankton biomass was similarly enhanced, possibly due to differential physical and biological aggregation mechanisms, and resulted in important zooplankton-mediated changes in mesoscale biogeochemistry.  相似文献   

13.
Using geographic information systems (GIS) software and geostatistical techniques, we utilized three decades of water-column chlorophyll a data to examine the relative importance of autochthonous versus allochthonous sources of reduced carbon to benthic communities that occur from the northern Bering to the eastern Beaufort Sea shelf. Spatial trend analyses revealed areas of high benthic biomass (>300 g m−2) and chlorophyll (>150 mg m−2) on both the southern and northern Chukchi shelf; both areas are known as depositional centers for reduced organic matter that originates on the Bering Sea shelf and is advected northward in Anadyr and Bering shelf water masses. We found a significant correlation between biomass and chlorophyll a in the Chukchi Sea, reflective of the strong benthic–pelagic coupling in a system that is utilized heavily by benthic-feeding marine mammals. In contrast, there was no significant correlation between biomass and chlorophyll in the Beaufort Sea, which by comparison, is considerably less productive (biomass and chlorophyll, <75 g m−2 and <50 mg m−2, respectively). One notable exception is an area of relatively high biomass (50–100 g m−2) and chlorophyll (80 mg m−2) near Barter Island in the eastern Beaufort Sea. Compared to other adjacent areas in the Beaufort Sea, the chlorophyll values in the vicinity of Barter Island were considerably higher and likely reflect a long-hypothesized upwelling in that area and close coupling between the benthos and autochthonous production. In the Bering Sea, a drop in benthic biomass in 1994 compared with previous measurements (1974–1993) may support earlier observations that document a decline in biomass that began between the 1980s and 1990s in the Chirikov Basin and south of St. Lawrence Island. The results of this study indicate that the benthos is an excellent long-term indicator of both local and physical advective processes. In addition, this work provides further evidence that secondary production on arctic shelves can be significantly augmented by reduced carbon advected from highly productive adjacent shelves.  相似文献   

14.
The vertical flux of particulate matter at 330 m depth in San Lázaro Basin off southern Baja California ranged from 63 to 587 mg m−2 d−1 between August and November 1996. Organic carbon contents were between 5.6 and 14.8%, yielding flux rates of 9–40 mgC m−2 d−1. In December 1997 and January 1998, at the height of the strong El Niño event, the respective fluxes (47–202 mg m−2 d−1 and 3–8 mgC m−2 d−1) were comparable. The February–June 1998 records, however, revealed sharply reduced mass (1–6 mg m−2 d−1) and organic carbon (0.2–0.8 mgC m−2 d−1) fluxes. The organics collected in 1996 were predominantly autochthonous (δ13C=−22‰; C/N=8). The variations in δ15N (8.3–11.0‰) suggest an alternation of new and regenerated production, possibly associated with fluctuations in the intensity of deep mixing during that autumn. The relatively high organic matter fluxes in December 1997 appear to be associated with regenerated production. The average composition from February to June 1998 (δ13C=−23.6‰; 15N=11.7‰; C/N=10.5) indicates degraded material of marine origin. The maximum δ15N value found (14‰) suggests that deeper, denitrified waters were brought to the surface and possibly advected laterally. Regime changes in the waters of the basin occur at 6–10 week intervals, evidenced by concurrent shifts in most of the measured parameters, including fecal pellet types and metal chemistry. The marine snow-dominated detritus collected showed a shift from a mixed diatom-rich-radiolarian-coccolith assemblage in late 1996 to a coccolith-dominated assemblage, including the contents of fecal pellets, during the 1997–1998 El-Niño period. T–S profiles, plankton analysis and chlorophyll contents of the upper water column indicated that the strong phytoplankton bloom, normally associated with seasonal upwelling along the Pacific coast of Baja, did not occur during the spring of 1998. The persistence of oligotrophic conditions during the 1997–1998 El Niño event favored the dominance of nanoplankton and reduced the vertical flux of particles.  相似文献   

15.
The Great Belt, the Øresund and the Little Belt connect the central Baltic Sea and the Kattegat. A fixed station was moored in the contraction area in the Little Belt during the period 18–28 July 1995, measuring temperature, salinity and current in two levels, while discharge was measured by the RVDana. The composite Froude number calculated at the fixed station shows that the two layer flow through this area was most often supercritical. The discharges were satisfactorily related to the currents measured at the fixed station, and time-series of transports through the Little Belt were established. When compared to the transports through the Øresund the water transport ratio (Øresund:Little Belt) was found to be 4·4, while the salt transport ratio was found to be 3·0. The resistance of the Little Belt, when considering the differences in sea level from Gedser to Hornbæk, was 1839×10−12 s2 m−5. On the basis of water level and surface salinity measurements made during the period 1931–76, a net discharge of 2300 m3 s−1and a net salt transport of 36 tonnes s−1through the Little Belt from the central Baltic Sea were found.  相似文献   

16.
During the CINCS project (Pelagic–benthic Coupling IN the oligotrophic Cretan Sea—NE Mediterranean), a single mooring with two sediment traps (at 200 and 1515m water depth) and two current meters was deployed in the southern Cretan Sea margin at a depth of 1550 m. A second mooring deployed at the 500 m station was lost, as a result of fishing activities. The duration of the study was 12 months (November 1994 to November 1995) with sampling intervals of 15 or 16 days. The traps were retrieved, serviced and the sedimented material was collected every 6 months. In total, 48 samples were collected (24 from each trap) throughout the study period and fluxes of total particulate mass, opal, organic matter, carbonates, and lithogenic component were measured. Natural radionuclides (210Po and 210Pb) were determined for all trap samples. Total mass flux and the fluxes of four major constituents increased with depth, the total mass flux reaching values of nearly 550 mg m−2 d−1 at 1515 m and 187 mg m−2 d−1 at 200 m depth, following the same patterns observed in other experiments (ECOMARGE, SEEP-I, SEEP-II). The mean annual mass fluxes were 209 and 49.8 mg m−2 d−1 at the near bottom and near surface trap respectively. This suggests that lateral transport of particulate matter is of importance in the area. Total mass fluxes at the two depths were characterized by different seasonal fluctuations, although a general decreasing trend was observed from the I (winter) to the II (summer) deployment at both depths. This was mainly a result of reductions in aluminosilicate inputs during the summer dry period. At 200 m depth carbonates were more important during winter, because of a large carbonate input consisting mainly of coccoliths of Emiliania huxleyi, while during the summer decreased fluxes of carbonates and aluminosilicates resulted in a reduction of the mass flux. In contrast, at 1515 m depth the lithogenic component was the dominant component during the winter deployment, indicating a terrigenous input. During the summer period the decrease in mass flux was strongly effected by the decrease in aluminosilicates. There was a diminution in the organic carbon content with a concomitant increase in total mass flux, which, together with the almost negligible increase in the annual 210Pb activity with depth and the increase of 210Po activity with depth could be interpreted as indicating a contribution of resuspended material to the input at 1515 m. The complex mesoscale circulation of the Cretan Sea, consisting of a cyclone (east)–anticyclone (west) system, controls particle transfer in the area. This hydrodynamic system seems to move water masses towards the southern Cretan Sea margin, and consequently carry materials from the open sea to the upper slope and shelf.  相似文献   

17.
Young Sound is a deep-sill fjord in NE Greenland (74°N). Sea ice usually begins to form in late September and gains a thickness of 1.5 m topped with 0–40 cm of snow before breaking up in mid-July the following year. Primary production starts in spring when sea ice algae begin to flourish at the ice–water interface. Most biomass accumulation occurs in the lower parts of the sea ice, but sea ice algae are observed throughout the sea ice matrix. However, sea ice algal primary production in the fjord is low and often contributes only a few percent of the annual phytoplankton production. Following the break-up of ice, the immediate increase in light penetration to the water column causes a steep increase in pelagic primary production. Usually, the bloom lasts until August–September when nutrients begin to limit production in surface waters and sea ice starts to form. The grazer community, dominated by copepods, soon takes advantage of the increased phytoplankton production, and on an annual basis their carbon demand (7–11 g C m−2) is similar to phytoplankton production (6–10 g C m−2). Furthermore, the carbon demand of pelagic bacteria amounts to 7–12 g C m−2 yr−1. Thus, the carbon demand of the heterotrophic plankton is approximately twice the estimated pelagic primary production, illustrating the importance of advected carbon from the Greenland Sea and from land in fuelling the ecosystem.In the shallow parts of the fjord (<40 m) benthic primary producers dominate primary production. As a minimum estimate, a total of 41 g C m−2 yr−1 is fixed by primary production, of which phytoplankton contributes 15%, sea ice algae <1%, benthic macrophytes 62% and benthic microphytes 22%. A high and diverse benthic infauna dominated by polychaetes and bivalves exists in these shallow-water sediments (<40 m), which are colonized by benthic primary producers and in direct contact with the pelagic phytoplankton bloom. The annual benthic mineralization is 32 g C m−2 yr−1 of which megafauna accounts for 17%. In deeper waters benthic mineralization is 40% lower than in shallow waters and megafauna, primarily brittle stars, accounts for 27% of the benthic mineralization. The carbon that escapes degradation is permanently accumulated in the sediment, and for the locality investigated a rate of 7 g C m−2 yr−1 was determined.A group of walruses (up to 50 adult males) feed in the area in shallow waters (<40 m) during the short, productive, ice-free period, and they have been shown to be able to consume <3% of the standing stock of bivalves (Hiatella arctica, Mya truncata and Serripes Groenlandicus), or half of the annual bivalve somatic production. Feeding at greater depths is negligible in comparison with their feeding in the bivalve-rich shallow waters.  相似文献   

18.
Using the seawater dilution technique, we measured phytoplankton growth and microzooplankton grazing rates within and outside of the 1999 Bering Sea coccolithophorid bloom. We found that reduced microzooplankton grazing mortality is a key component in the formation and temporal persistence of the Emiliania huxleyi bloom that continues to proliferate in the southeast Bering Sea. Total chlorophyll a (Chl a) at the study sites ranged from 0.40 to 4.45 μg C l−1. Highest phytoplankton biomass was found within the bloom, which was a mixed assemblage of diatoms and E. huxleyi. Here, 75% of the Chl a came from cells >10 μm and was attributed primarily to the high abundance of the diatom Nitzschia spp. Nutrient-enhanced total phytoplankton growth rates averaged 0.53 d−1 across all experimental stations. Average growth rates for >10 μm and <10 μm cells were nearly equal, while microzooplankton grazing varied among stations and size fractions. Grazing on phytoplankton cells >10 μm ranged from 0.19 to 1.14 d−1. Grazing on cells <10 μm ranged from 0.02 to 1.07 d−1, and was significantly higher at non-bloom (avg. 0.71 d−1) than at bloom (avg. 0.14 d−1) stations. Averaged across all stations, grazing by microzooplankton accounted for 110% and 81% of phytoplankton growth for >10 and <10 μm cells, respectively. These findings contradict the paradigm that microzooplankton are constrained to diets of nanophytoplankton and strongly suggests that their grazing capability extends beyond boundaries assumed by size-based models. Dinoflagellates and oligotrich ciliates dominated the microzooplankton community. Estimates of abundance and biomass for microzooplankton >10 μm were higher than previously reported for the region, ranging from 22,000 to 227,430 cells l−1 and 18 to 164 μg C l−1. Highest abundance and biomass occurred in the bloom and corresponded with increased abundance of the large ciliate Laboea, and the heterotrophic dinoflagellates Protoperidinium and Gyrodinium spp. Despite low grazing rates on phytoplankton <10 μm within the bloom, the abundance and biomass of small microzooplankton (<20 μm) capable of grazing E. huxleyi was relatively high at bloom stations. This body of evidence, coupled with observed high grazing rates on large phytoplankton cells, suggests the phytoplankton community composition was strongly regulated by herbivorous activity of microzooplankton. Because grazing behavior deviated from size-based model predictions and was not proportional to microzooplankton biomass, alternate mechanisms that dictate levels of grazing activity were in effect in the southeastern Bering Sea. We hypothesize that these mechanisms included morphological or chemical signaling between phytoplankton and micrograzers, which led to selective grazing pressure.  相似文献   

19.
During the EPOS leg 2 cruise (European Polarstern Study, November 1988–January 1989), the production rate of biogenic silica in the euphotic zone was measured by the 30Si method at stations in the Scotia and Weddell Seas.The highest integrated production rates were observed in the Scotia Sea (range: 11.2–20.6 mmol Si m−2 day−1), the marginal ice zone of the Weddell Sea exhibiting somewhat lower values (range: 6.0–20.0 mmol Si m−2day−1).Our results demonstrate that as far as biogenic silica production is concerned the marginal ice zone of the Weddell Sea is considerably less productive than that of the Ross Sea. Our results also indicate that the water of the Antarctic Circumpolar Current (ACC) could be more productive in late spring and early summer than at the beginning of spring. Possible reasons for the differences among the three subsystems (Ross Sea, Weddell Sea and ACC) are discussed.  相似文献   

20.
During nine field transplant tests in San Diego Bay (1987–1990), juvenile mussels were exposed to mean concentrations of tributyltin (TBT) in ambient seawater ranging from 2 to 530 ng liter−1 for 12 weeks under natural conditions. A total of 79 cages with 18 mussels each were monitored at 18 different sites. Growth and seawater TBT concentrations were measured weekly or on alternate weeks (biweekly). Mean growth rates ranged from 17 to 505 mg week−1 (0·2 to 2·5 mm week−1). Accumulation of TBT in mussel tissues was measured at the end of each 12-week test exposure and ranged from 0·1 to 3·2 μg g−1 TBT wet weight. The frequency of the measurements and the integration of chemical and biological measurements improved the accuracy of the assessment over more traditional approaches. Growth was significantly related to seawater and tissue TBT. The statistical relationships with growth effects were used to estimate chemical effect zones for TBT in San Diego Bay. Site-specific differences were distinguished by additional statistical analyses and consideration of environmental significance.  相似文献   

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