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1.
The governments around the Baltic Sea have agreed on a new set of targets for nutrient load reductions. The major motive for this is new and better knowledge about the link between nutrient loads and water transparency in different parts of the sea. The Baltic Sea Action Plan (BSAP) defines target for transparency in different marine basins, the load reductions necessary to meet transparency targets and a scheme for the distribution of the abatement burden between countries adjacent to the sea.  相似文献   

2.
The concentration of dissolved and particulate Re have been measured in the Narmada, Tapi and the Mandovi estuaries in the Arabian Sea and the Hooghly estuary in the Bay of Bengal. Re concentration in water and particulate matter of these estuaries is highly variable. Re in river waters analysed varies from 1 to 41 pmol/kg, the lowest in the Mandovi and the highest in the Mahi river. Re concentrations in the rivers analysed except in the Mandovi river are higher than the average global riverine Re concentration of 2.1 pmol/kg. Based on this study and the available data, the contemporary global annual flux of dissolved riverine Re is estimated to be ~ 350 × 103 mol with an average concentration of ~ 9.2 pmol/kg, much higher than the earlier estimates. Residence time of Re in the oceans based on this estimate is 175,000 years, ~ 4 times lower compared to earlier estimates. Re behaves conservatively in all the estuaries studied. Re concentrations of seawater in the Bay of Bengal and in the Arabian Sea, estimated from the data of the Hooghly and the Mandovi estuaries respectively are ~ 40 pmol/kg, similar to the open ocean Re values of the Arabian Sea measured in this study and the values reported for in other oceanic regions. However, the dissolved Re in the Gulf of Cambay is 2 to 5 times higher, consistent with the high Re measured in the Mahi estuary and in the coastal waters of the Gulf of Cambay. The source of high Re in the Gulf of Cambay seems to be anthropogenic, measurements of Re in rivers and industrial waste waters draining into the Gulf supply amount to ~ 2300 mol of Re annually. This anthropogenic supply coupled with high residence time of water in the Gulf contribute to its high Re. Re concentration in suspended sediments of the Narmada estuary varies from 1 to 2 pmol/g, and does not show any discernible trend with salinity.The contemporary global riverine Re supply to the oceans estimated in this study is ~ 2–4 times higher compared to its removal in the reducing (anoxic/suboxic) sediments, indicating non-steady state of Re in the ocean. High dissolved riverine Re flux coupled with high Re content in the Gulf of Cambay highlights the need of a detailed study of Re in the various global rivers and in oceans including coastal regions and semi enclosed basins of the world to understand its behaviour in various reservoirs and to constrain the residence time of Re in the ocean.  相似文献   

3.
Seven years (2001–2008) of dissolved organic carbon (DOC) vertical profiles were examined in order to assess the main processes determining DOC concentration and distribution in the meso- and bathypelagic layers of the Mediterranean Sea. As expected, DOC showed high and highly variable concentrations in the surface layer of 57–68 μM (average values between 0 and 100 m), with a decrease to 44–53 μM between 200 and 500 m. Deep DOC distribution was strongly affected by deep-water formation, with a significant increase to values of 76 μM in recently ventilated deep waters, and low concentrations, comparable to those observed in the open oceanic waters (34–45 μM), where the oldest, deep waters occurred. In winter 2004/2005 a deep-water formation event was observed and the consequent DOC export at depth was estimated to range between 0.76–3.02 Tg C month–1. In the intermediate layer, the main path of the Levantine Intermediate Water (LIW) was followed in order to estimate the DOC consumption rate in its core. Multiple regression between DOC, apparent oxygen utilization (AOU), and salinity indicated that 38% of the oxygen consumption was related to DOC mineralization when the effect of mixing was removed. In deep waters of the southern Adriatic Sea a DOC decrease of 6 μM, together with an AOU increase of 9 μM, was observed between the end of January 2008 and the end of June 2008 (5 months). These data indicate a rate of microbial utilization of DOC of about 1.2 μM C month−1, with 92% of the oxygen consumption due to DOC mineralization. These values are surprisingly high for the deep sea and represent a peculiarity of the Mediterranean Sea.  相似文献   

4.
Waves at 15 m water depth in the northern Arabian Sea are measured during the summer monsoon for a period of 45 days and the characteristics are described. The significant wave height varied from 1.1 to 4.5 m with an average value of 2.5 m. 75% of the wave height at the measurement location is due to the swells arriving from the south-west and the remaining is due to the seas from south-west to north-west. Wave age of the measured data indicates that the waves in the nearshore waters of northern Arabian Sea during the summer monsoon are swells with young sea.  相似文献   

5.
Dissolved and particulate Mn concentrations were investigated on a seasonal scale in surface waters of the NW German Wadden Sea (Spiekeroog Island) in 2002 and 2003. As the Wadden Sea forms the transition zone between the terrestrial and marine realms, Mn was analysed in coastal freshwater tributaries and in the adjoining German Bight as well. Additionally, sediments and porewaters of the tidal flat sediments were analysed for Mn partitioning and microbial activity.Dissolved Mn concentrations show strong tidal and seasonal variation with elevated concentrations during summer at low tide. Summer values in the Wadden Sea (av. 0.7 μM) are distinctly higher than in the central areas of the German Bight (av. 0.02 μM), suggesting a possible impact of the Wadden Sea environment on the Mn budget of the North Sea. Seasonality is also observed for particulate Mn in the Wadden Sea (winter av. 800 mg kg− 1; summer av. 1360 mg kg− 1). Although particles are relatively Mn-poor during winter, the high SPM load during this season causes elevated excess concentrations of particulate Mn, which in part exceed those of the dissolved phase. Therefore, winter values cannot be ignored in balance calculations for the Wadden Sea system.Porewater Mn concentrations differ depending on sediment type and season. Maximum concentrations are found in surface sediments at a mixed flat site (190 μM) during summer, while winter values are distinctly lower. This indicates that enhanced microbial activity owing to higher temperature during summer leads to increased reduction of Mn-oxides in surface sediments and enhances the corresponding diffusive and advective Mn flux across the sediment-water interface. Draining of Mn-rich porewaters from sediments is also documented by analyses of tidal creek waters, which are highly enriched in Mn during summer.Furthermore, an important Mn source is freshwater discharged into the Wadden Sea via a flood-gate. The concentration of dissolved Mn in freshwater was highly variable during the sampling campaigns in 2002 and 2003, averaging 4 μM. In contrast, particulate Mn displayed a seasonal behaviour with increasing contents during summer. On the basis of salinity variations in the Wadden Sea, the total amount of Mn contributed to the Wadden Sea via freshwater was estimated. This balance shows the importance of the freshwater environment for the Mn inventory of the Wadden Sea. During winter the total Mn inventory of the Wadden Sea water column may be explained almost completely by freshwater discharge, whereas in summer the porewater system forms the dominating source.  相似文献   

6.
Variations in the nutrient concentrations were studied during two cruises to the Arabian Sea. The situation towards the end of the southwest monsoon season (September/October 1994) was compared with the inter-monsoonal season during November and December 1994. Underway surface transects showed the influence of an upwelling system during the first cruise with deep, colder, nutrient-rich water being advected into the surface mixed layer. During the southwesterly monsoon there was an area of coastal Ekman upwelling, bringing colder water (24.2°C) into the surface waters of the coastal margin. Further offshore at about 350 km there was an area of Ekman upwelling, as a result of wind-stress curl, north of the Findlater Jet axis; this area also had cooler surface water (24.6°C). Further offshore (>1000 km) the average surface temperatures increased to >27°C. These waters were oligotrophic with no evidence of the upwelling effects observed further inshore. In the upwelling regions nutrient concentrations in the close inshore coastal zone were elevated (NO3=18 μmol l-1, PO4=1.48 μmol l-1); higher concentrations also were measured at the region of offshore upwelling off the shelf, with a maximum nitrate concentration of 12.5 μmol l-1 and a maximum phosphate concentration of 1.2 μmol l-1. Nitrate and phosphate concentrations decreased with increasing distance offshore to the oligotrophic waters beyond 1400 km, where typical nitrate concentrations were 35.0 nmol l-1 (0.035 μmol l-1) in the surface mixed layer. A CTD section from the coastal shelf, to 1650 km offshore to the oligotrophic waters, clearly showed that during the monsoon season, upwelling is one of the major influences upon the nutrient concentrations in the surface waters of the Arabian Sea off the coast of Oman. Productivity of the water column was enhanced to a distance of over 800 km offshore. During the intermonsoon period a stable surface mixed layer was established, with a well-defined thermocline and nitracline. Surface temperature was between 26.8 and 27.4°C for the entire transect from the coast to 1650 km offshore. Nitrate concentrations were typically between 2.0 and 0.4 μmol l-1 for the transect, to about 1200 km where the waters became oligotrophic, and nitrate concentrations were then typically 8–12 nmol l-1. Ammonia concentrations for the oligotrophic waters were typically 130 nmol l-1, and are reported for the first time in the Indian Ocean. The nitrogen/phosphorus (N/P) ratios suggest that phytoplankton production was potentially nitrogen-limited in all the surface waters of the Arabian Sea, with the greatest nitrogen limitation during the intermonsoon period.  相似文献   

7.
We examined bacterioplankton biomass and heterotrophic production (BHP) during summer stratification in the northwestern Mediterranean in four successive stratification seasons (June–July of 1993–1996). Values of phytoplankton biomass and primary production were determined simultaneously so that the data sets for autotrophic and heterotrophic microbial plankton could be compared. Three standard stations were set along a transect from Barcelona to the channel between Mallorca and Menorca, representing coastally influenced shelf waters, frontal waters over the slope front, and open sea waters. Conversion factors from 3H-leucine incorporation to BHP were empirically determined and varied between 0.29 and 3.25 kg C mol-1. Bacterial biomass values were among the lowest found in any marine environment. BHP values (between 0.02 and 2.5 μg C L-1 d-1) were larger than those of low nutrient low chlorophyll areas such as the Sargasso Sea and lower than those from high nutrient low chlorophyll areas such as the equatorial Pacific. Growth rates of bacterioplankton were highest at the slope front (0.20 d-1) and lowest at the open sea station (0.04 d-1). Phytoplankton growth rates were similar at the three stations (∼0.50 d-1). Integrated values of bacterioplankton biomass, BHP and bacterial growth rates did not show significant differences among years, but differences between the three stations were clearly significant. Phytoplankton biomass, primary production, and phytoplankton growth rates did not show significant differences either with year or with station. As a consequence the bacterioplankton to phytoplankton biomass (BB/BPHY) and production (BHP/PP) ratios varied from the coastal to the open sea stations. The BB/BPHY ratio was 0.98 at the coast and ∼0.70 at the other two stations. These ratios are similar to those found in other oligotrophic marine environments. The BHP/PP ratio was 0.83 at the coast, 0.36 at the slope and 0.09 at the open sea station. The last value is also similar to values found in other oligotrophic marine environments. Vertical distribution of these ratios was also examined.The comparison of microbial parameters at the three stations indicates a different kind of relationship between bacterioplankton and phytoplankton in oligotrophic open sea waters and in coastal, nutrient-richer waters. According to such parameters and to the values of the BB/BPHY and BHP/PP ratios, open waters in the northwestern Mediterranean (despite their relatively short distance from the shore) were intermediate between the extremely oligotrophic waters of the eastern Mediterranean or the Sargasso Sea and the more productive waters of the equatorial Pacific.  相似文献   

8.
We determined the distributions and fluxes of methyl chloride and methyl bromide in the East China Sea (ECS) and the Southern Yellow Sea (SYS) in November 2007. Methyl chloride and methyl bromide concentrations in the surface waters ranged from 47.1 to 163 pmol L?1 and from 0.70 to 9.82 pmol L? 1, with average values of 87.6 and 2.97 pmol L? 1, respectively. The distributions of the two methyl halides were clearly influenced by the Yangtze (Changjiang) River effluent and Kuroshio water, with high concentrations appearing in the coastal zone and low values occurring in the open waters. A positive linear correlation was observed between methyl chloride and methyl bromide concentration anomalies in the surface waters, suggesting that they may share some origins in this coastal area. However, no correlation was found between the two methyl halide concentration anomalies and chlorophyll a in the surface waters. The vertical profiles of the two methyl halides were characterized by the maxima in the upper mixed layer. Both gases were generally supersaturated in the surface seawater, with mean sea-to-air fluxes of methyl chloride and methyl bromide of 391 and 20.0 nmol m?2 d? 1, respectively.  相似文献   

9.
The concentration of dimethylsulfide (DMS) and supporting parameters were determined in surface seawater and vertical profiles at 26 stations in the South China Sea. The concentrations of DMS in surface seawater ranged from 61 to 148 ng S/l, with a mean of 82 ng S/l. High concentrations of DMS were found in the productive regions. The vertical profiles of DMS were characterized by a maximum at depths typically between 20 and 75 m. The concentrations of DMS were correlated with the levels of chlorophyll a both in the surface seawater and in the vertical distribution. The concentrations of DMS were higher than expected for this chlorophyll-poor tropical sea, as indicated by markedly high DMS (ng S/l)/chlorophyll a (μg/l) ratios ranging from 315 to 3524 with a mean of 1768 for all the surface seawater samples. DMS concentration was significantly correlated with seawater temperature and dissolved oxygen, but it showed an inverse relationship to nutrients (including nitrate, phosphate and silicate). On the basis of sea surface concentrations of DMS and gas exchange calculations, the mean flux of DMS from the South China Sea to the atmosphere was estimated to be 5.5 μmol m−2 d−1.  相似文献   

10.
Data collected from hydrographic stations occupied within the Venezuelan and Columbian basins of the Caribbean Sea from 1922 through 2003 are analyzed to study the decadal variability of deep temperature in the region. The analysis focuses on waters below the 1815-m sill depth of the Anegada–Jungfern Passage. Relatively dense waters (compared to those in the deep Caribbean) from the North Atlantic spill over this sill to ventilate the deep Caribbean Sea. Deep warming at a rate of over 0.01 °C decade–1 below this sill depth appears to have commenced in the 1970s after a period of relatively constant deep Caribbean Sea temperatures extending at least as far back as the 1920s. Conductivity–temperature–depth station data from World Ocean Circulation Experiment Section A22 along 66°W taken in 1997 and again in 2003 provide an especially precise, albeit geographically limited, estimate of this warming over that 6-year period. They also suggest a small (0.001 PSS-78, about the size of expected measurement biases) deep freshening. The warming is about 10 times larger than the size of geothermal heating in the region, and is of the same magnitude as the average global upper-ocean heat uptake over a recent 50-year period. Together with the freshening, the warming contributes about 0.012 m decade–1 of sea level rise in portions of the Caribbean Sea with bottom depths around 5000 m.  相似文献   

11.
The relationship between the spring bloom along the Primorye coast and the sea ice of the Tatarskiy Strait in the northern region of the East/Japan Sea, a semi-enclosed marginal sea in the North Pacific, was investigated using the ten-year SeaWiFS chlorophyll-a concentration data and DMSP/SSMI sea ice concentration data from 1998 to 2007. Year-to-year variations in the chlorophyll-a concentrations in the spring were positively correlated with those of the sea ice concentrations in the Tatarskiy Strait in the previous winter with a correlation coefficient of 0.77. Abrupt increases in nutrients, essential for the spring bloom in the upper ocean during spring, were supplied from sea ice-melted waters. Time series of vertical distributions of the nutrients indicated that phosphate concentrations were extremely elevated in the upper ocean (less than 100 m) without any connection to high concentrations in the deep waters below. The water mass from sea ice provided preferable conditions for the spring bloom through changes in the vertical stratification structure of the water columns. Along-coast ratios of stability parameters between two neighboring months clearly showed the rapid progression of the generation of a shallow pycnocline due to fresh water originating from sea ice. This study addressed the importance of the physical environment for biogeochemical processes in semi-enclosed marginal seas affected by local sea ice.  相似文献   

12.
Despite the fact that marine viruses have been increasingly investigated in the last decade, knowledge on virus abundance, biomass and distribution in mesopelagic and bathypelagic waters is limited. We report here the results of a large-spatial-scale study (covering more than 3000 km) on the virioplankton distribution in epi-, meso- and bathypelagic waters in 19 areas of the Mediterranean Sea, from the Alboran Sea and Western Mediterranean, to the Tyrrhenian Sea, Sicily Channel and Ionian Sea. Integrated viral abundance in epipelagic waters was significantly higher than in deep-sea waters (on average, 2.4 vs. 0.5×1012 viruses m−3). However, abundance of viruses in the deep-Mediterranean waters was the highest reported so far for deep seas worldwide (7.0 and 3.1×1011 viruses m−3 in mesopelagic and bathypelagic waters, respectively) and their biomass accounted for 13–18% of total prokaryotic C biomass. The significant relationship between viral abundance and prokaryotic abundance and production in deep waters suggests that also deep-sea viruses are closely dependent on the abundance and metabolism of their hosts. Moreover, virus to prokaryote (and nucleoid-containing cell (NuCC)) abundance ratio increased with increasing depths suggesting that deep waters may represent optimal environments for viral survival or proliferation. Overall, our results indicate that deep waters may represent a significant reservoir of viruses and open new perspectives for future investigations of viral impact on the functioning of meso-bathypelagic ecosystems.  相似文献   

13.
Primary production, nutrient concentrations, phytoplankton biomass (incl. chlorophyll a) and water transparency (Secchi depth), are important indicators of eutrophication. Earlier basin-wide primary production estimates for the Baltic Sea, a shallow shelf sea, were based mainly on open-sea data, neglecting the fundamentally different conditions in the large river plumes, which might have substantially higher production. Mean values of the period 1993–1997 of nutrient concentrations (phosphate, nitrate, ammonium and silicate), phytoplankton biomass, chlorophyll a (chl a) concentration, turbidity and primary production were calculated in the plumes of the rivers Oder, Vistula and Daugava and Klaipeda Strait as well as the open waters of the Arkona Sea, Bornholm Sea, eastern Gotland Sea and the Gulf of Riga. In the plumes, these values, except for primary production, were significantly higher than in the open waters. N:P ratios in the plumes were >16 (with some exceptions in summer and autumn), indicating potential P-limitation of phytoplankton growth, whereas they were <16 in the open Baltic Proper, indicating potential N-limitation. On the basis of in situ phytoplankton primary production, phytoplankton biomass and nutrient concentrations, the large river plumes and the Gulf of Riga could be characterized as eutrophic and the outer parts of the coastal waters and the open sea as mesotrophic. Using salinity to define the border of the plumes, their mean extension was calculated by means of a circulation model. Taking into account the contribution of coastal waters, the primary production in the Baltic Proper and the Gulf of Riga was 42·6 and 4·3×106 t C yr−1, respectively. Hence, an annual phytoplankton primary production in the whole Baltic Sea was estimated at 62×106 t C yr−1. The separate consideration of the plumes had only a minor effect on the estimation of total primary production in comparison with an estimate based on open sea data only. There is evidence for a doubling of primary production in the last two decades. Moreover, a replacement of diatoms by dinoflagellates during the spring bloom was noticed in the open sea but not in the coastal waters. A scheme for trophic classification of the Baltic Sea, based on phytoplankton primary production and biomass, chl a and nutrient concentrations, is proposed.  相似文献   

14.
Concentrations of dissolved Al and Fe in the surface mixed layer were measured during five cruises of the 1995 US JGOFS Arabian Sea Process Study, Concentrations of both Al and Fe were relatively uniform between January and April, the NE Monsoon and the Spring Intermonsoon period, ranging from 2 to 11 nM Al (mean 5.3 nM) and 0.5 to 2.4 nM Fe (mean 1.0 nM). In July/August, after the onset of the SW Monsoon, surface water Al and Fe concentrations increased significantly (Al range 4.5–20.1 nM; mean=10 nM, Fe range 0.57–2.4 nM; mean=1.3 nM), particularly in the NE part of the Arabian Sea, as the result of the input and partial dissolution of eolian dust. Using the enrichment of Al in the surface waters, we estimate this is the equivalent to the deposition of 2.2–7.4 g m−2 dust, which is comparable to values previously estimated for this region. Approximately one month later (August/September), surface water concentrations of both Al and Fe were found to have decreased significantly (mean Al 7.4 nM, mean Fe 0.90 nM) particularly in the same NE region, as the result of export of particulate material from the euphotic zone. Fe supply to the surface waters is also affected by upwelling of sub-surface waters in the coastal region of the Arabian Sea during the SW Monsoon. Despite the proximity of high concentrations of Fe in the shallow sub-oxic layer, freshly upwelled water is not drawn from this layer and the NO3/Fe ratio in the initially upwelled water is below the value at which Fe limitation is through to occur. Continued deposition of eolian Fe into the upwelled water as it advects offshore provides the Fe required to raise this ratio above the Fe limitation value.  相似文献   

15.
Large areas of the bottom sediments of the Baltic Sea are temporarily or permanently anoxic. These sediments are also an important sink for a variety of contaminants. Reoxygenation of bottom waters allows recolonisation by benthic infauna, which may have important implications for the fate of buried contaminants. This study used tracers to experimentally examine the role of bioturbation by benthic infauna in transporting sediment-associated contaminants in the Baltic Sea. Three different tracer methods were used in two experiments, using three key Baltic macrofaunal species: the amphipod crustacean Monoporeia affinis; the Baltic clam Macoma baltica; and the priapulid worm Halicryptus spinulosus. In the first experiment, a reoxygenation–recolonisation scenario was recreated in the laboratory, using hypoxic sediment cores collected in the field, to determine if there was remobilisation of buried 137Cs from the Chernobyl nuclear accident in 1986. The potential for the infauna to bury newly settled surface contamination was also investigated, using a fluorescent particle tracer. In the second experiment, artificially-created radiolabelled tracer layers (14C and 51Cr) were used to quantify both upward and downward movements of organic matter and sediment-associated contaminants by bioturbation.In both experiments there were clear visual differences between the sediment effects of the three species. Halicryptus spinulosus buried deepest into the sediment, creating a network of burrows, Monoporeia affinis burrowed actively in the upper few centimeters of the sediment, and Macoma baltica was quite stationary, but appeared to filter- and deposit feed at the sediment surface. Mixing depths in the hypoxic sediment varied from 4.0 ± 3.5 cm for M. baltica to 7.8 ± 2.1 cm for H. spinulosus. Biodiffusion rates (Db) were similar for all treatments but biotransport rates (r) were significantly different between treatments, mainly due to a high r value for H. spinulosus. In the experiment with radiolabelled tracer layers, 51Cr was transported more than 14C, and tracer originally at the surface transported more than tracer buried 4 cm below the surface. There was also transport of all tracers in treatments without added macrofauna. The most likely explanation is bioturbation by the meiofauna that were undoubtedly present in both experiments.Bioturbation by macrofauna both buries surface contaminants and remobilises those that are buried, but the effects are small and on a similar scale to transport caused by meiofauna. In addition, 137Cs profiles at the hypoxic site indicated that resuspension and redeposition of sediment by physical processes had occurred, and also showed that contaminants from the last 40 years were still present in the top 5–10 cm of the sediment, well within active mixing depths. At this site, as at many others in the Baltic, physical processes are likely to be far more important than biological processes in the redistribution of contaminants on a decadal timescale.  相似文献   

16.
Mass fluxes of diatom opal, planktonic foraminifera carbonate and coccolithophorid carbonate were measured with time-series sediment traps at six sites in the Arabian Sea, Bay of Bengal and Equatorial Indian Ocean (EIOT). The above fluxes were related to regional variations in salinity, temperature and nutrient distribution. Annual fluxes of diatom opal range between 3 and 28 g m−2 yr−1, while planktonic foraminifera carbonate fluxes range between 6 and 23 g m−2 yr−1 and coccolithophorid carbonate fluxes range between 4 and 24 g m−2 yr−1. Annual planktonic foraminifera carbonate to coccolithophorid carbonate ratios range between 0.8 and 2.2 and coccolithophorid carbonate to diatom opal ratios range between 0.5 and 3.3.In the western Arabian Sea, coccolithophorids are the major contributors to biogenic flux during periods of low nutrient concentrations. Coccolithophorid carbonate fluxes decrease and planktonic foraminiferal carbonate and diatom opal fluxes increase when nutrient-rich upwelled waters are advected over the trap site. In the oligotropic eastern Arabian Sea, coccolithophorid carbonate fluxes are high throughout the year. Planktonic foraminiferal carbonate fluxes are the major contributors to biogenic flux in the EIOT. In the northern and central Bay of Bengal, when surface salinity values drop sharply during the SW monsoon, there is a drastic reduction in planktonic foraminiferal carbonate fluxes, but coccolithophorid carbonate and diatom opal fluxes remain steady or continue to increase. Distinctly higher annual molar Sibio/Cinorg (>1) and Corg/Cinorg (>1.5) ratios are observed in the northern and central Bay of Bengal mainly due to lower foraminiferal carbonate production as a result of sharp salinity variations. We can thus infer that the enhanced freshwater supply from rivers should increase oceanic CO2 uptake. Its silicate supply favours the production of diatoms while the salinity drop produces conditions unfavourable for most planktonic foraminifera species.  相似文献   

17.
The Arctic Ocean has wide shelf areas with extensive biological activity including a high primary productivity and an active microbial loop within the surface sediment. This in combination with brine production during sea ice formation result in the decay products exiting from the shelf into the deep basin typically at a depth of about 150 m and over a wide salinity range centered around S ～33. We present data from the Beringia cruise in 2005 along a section in the Canada Basin from the continental margin north of Alaska towards the north and from the International Siberian Shelf Study in 2008 (ISSS-08) to illustrate the impact of these processes. The water rich in decay products, nutrients and dissolved inorganic carbon (DIC), exits the shelf not only from the Chukchi Sea, as has been shown earlier, but also from the East Siberian Sea. The excess of DIC found in the Canada Basin in a depth range of about 50–250 m amounts to 90±40 g C m?2. If this excess is integrated over the whole Canadian Basin the excess equals 320±140×1012 g C. The high DIC concentration layer also has low pH and consequently a low degree of calcium carbonate saturation, with minimum aragonite values of 60% saturation and calcite values just below saturation. The mean age of the waters in the top 300 m was calculated using the transit time distribution method. By applying a future exponential increase of atmospheric CO2 the invasion of anthropogenic carbon into these waters will result in an under-saturated surface water with respect to aragonite by the year 2050, even without any freshening caused by melting sea ice or increased river discharge.  相似文献   

18.
Dimethylsulfoxide (DMSO) is an important degradation product of the climate-influencing gas dimethylsulfide (DMS). In the Ross Sea, Antarctica, dissolved DMSO (DMSOd) concentrations exhibited substantial seasonal and vertical variations. Surface water DMSOd concentrations in pre-bloom waters were very low (<1 nM) but increased rapidly up to 41 nM during the spring Phaeocystis antarctica bloom (late November). Increases in DMSOd concentrations lagged by several days increases in DMS concentrations. Although DMSOd concentrations reached relatively high levels during the spring bloom, concentrations were generally higher (36.3–60.6 nM) during summer (January), even though phytoplankton biomass and DMS concentrations had decreased by that time. During both seasons, DMSOd concentrations were substantially higher within the surface mixed layer than below it. DMSOd production from biological DMS consumption (BDMSC) was higher during late November (3.4–5.2 nM d?1) than during the summer (0.7–2.4 nM d?1); therefore, production via BDMSC alone could not explain the higher DMSOd concentrations encountered during the summer. Mixed layer-integrated DMSOd production from BDMSC was 2.5–13.7 times greater than production from dissolved DMS photolysis during the P. antarctica bloom, while photolysis contributed 1.3 times more DMSO than BDMSC before the bloom. The DMSO yield from BDMSC was consistently higher within the upper mixed layer than at depths below. Experimental incubations with water from the mixed layer showed that exposure to full spectrum sunlight for 72 h caused an increase in the DMSO yield whereas exposure to only photosynthetically active radiation did not. This suggests that ultraviolet radiation is a potential factor shifting the fate of biologically consumed DMS toward DMSO. In general, the highest DMSO yields from BDMSC were in samples with slow biological DMS turnover, whereas fast turnover favored sulfate rather than DMSO as a major end-product. This study provides the first detailed information about DMSOd distribution and production in the Ross Sea and points to DMSOd as an important biological and photochemical degradation product of DMS and a major reservoir of methylated sulfur in these polar surface waters.  相似文献   

19.
《Marine Chemistry》2006,98(2-4):210-222
This study presents concentrations of dimethylsulphide (DMS) and its precursor compound dimethylsulphoniopropionate (DMSP) in a variety of sea ice and seawater habitats in the Antarctic Sea Ice Zone (ASIZ) during spring and summer. Sixty-two sea ice cores of pack and fast ice were collected from twenty-seven sites across an area of the eastern ASIZ (64°E to 110°E; and the Antarctic coastline north to 62°S). Concentrations of DMS in 81 sections of sea ice ranged from < 0.3 to 75 nM, with an average of 12 nM. DMSP in 60 whole sea ice cores ranged from 25 to 796 nM and showed a negative relationship with ice thickness (y = 125x− 0.8). Extremely high DMSP concentrations were found in 2 cores of rafted sea ice (2910 and 1110 nM). The relationship of DMSP with ice thickness (excluding rafted ice) suggests that the release of large amounts of DMSP during sea ice melting may occur in discrete areas defined by ice thickness distribution, and may produce ‘hot spots’ of elevated seawater DMS concentration of the order of 100 nM. During early summer across a 500 km transect through melting pack ice, elevated DMS concentrations (range 21–37 nM, mean 31 nM, n = 15) were found in surface seawater. This band of elevated DMS concentration appeared to have been associated with the release of sea ice DMS and DMSP rather than in situ production by an ice edge algal bloom, as chlorophyll a concentrations were relatively low (0.09–0.42 μg l− 1). During fast ice melting in the area of Davis station, Prydz Bay, sea ice DMSP was released mostly as extracellular DMSP, since intracellular DMSP was negligible in both hyposaline brine (5 ppt) and in a melt water lens (4–5 ppt), while extracellular DMSP concentrations were as high as 149 and 54 nM, respectively in these habitats. DMS in a melt water lens was relatively high at 11 nM. During the ice-free summer in the coastal Davis area, DMS concentrations in surface seawater were highest immediately following breakout of the fast ice cover in late December (range 5–14 nM), and then remained at relatively low concentrations through to late February (< 0.3–6 nM). These measurements support the view that the melting of Antarctic sea ice produces elevated seawater DMS due to release of sea ice DMS and DMSP.  相似文献   

20.
Cu speciation was characterized at three stations in the sub arctic NW Pacific and Bering Sea using cathodic stripping voltammetry with the competing ligands benzoylacetone and salicylaldoxime. A single ligand model was fit to the titration data, yielding concentrations throughout the water column of ∼3–4 nM, and conditional stability constants ranging from 1012.7 to 1014.1, this range being partly due to the choice of competing ligand. Free Cu2+ in surface waters was 2–4×10−14 M, in close agreement with values reported by previous workers in the NE Pacific using anodic stripping voltammetry (ASV). However, those results showed that complexation by strong organic ligands becomes unimportant below 200–300 m, while our data indicated Cu is strongly complexed to depths as great as 3000 m. Free Cu2+ concentrations in surface waters reported here and in previous work are close to the threshold value where Cu can limit the acquisition of Fe by phytoplankton.  相似文献   

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