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1.
The distributions of the trace metals iron (Fe), copper (Cu) and cadmium (Cd) along with hydrological parameters (salinity, temperature and reactive phosphate) across the New Zealand continental shelf near Otago Peninsula have been studied. This is a region in which the Subtropical Convergence (STC), a major oceanic front separating subtropical and subantarctic waters, is uniquely located close to land, permitting an examination of the influence of terrestrial sources of Fe and Cu on oceanic waters containing excess micronutrients. Acid-soluble (110 nmol kg−1) and dissolved (6.3 nmol kg−1) Fe concentrations were highest over the central shelf, and decreased rapidly across the mixing zone of the STC to about 5 nmol kg−1 for both forms. The distribution of acid-soluble and dissolved Cu were similar to their counterparts for Fe. Depth-concentration profiles for acid-soluble Fe and Cu suggest resuspension of shelf sediments is the main source. The ratio of oxine-labile to acid-soluble Fe varied from 0.03 to 0.26, with the highest values found in the near surface waters. Oxine-labile Fe and Cu also decreased in concentration in a seawards direction, and with depth, indicating the influence of near surface processes on the reactivity of these elements. Cd concentrations across the continental shelf were very low (<200 pmol kg−1) and exhibited no clear spatial trend and no correlation with phosphate. Comparison of the Cd/P ratio across the shelf indicated that the waters in this region were strongly depleted in Cd relative to P. Phosphate concentrations were lowest in neritic water and increased in the seawards direction because of mixing with nutrient-rich Subantarctic Surface Water.  相似文献   

2.
Natural iron fertilization processes are occurring around the Crozet Islands (46°26′S–52°18′E), thus relieving the water masses from the normally encountered High Nutrients Low Chlorophyll (HNLC) conditions of the Southern Ocean. During austral summers 2004/2005 and 2005/2006, iron and aluminium concentrations were investigated in large particles (> 53 µm) collected from just below the mixed layer at stations under the influence of island inputs, and also in adjacent HNLC waters. These large particles are anticipated to sink out of the mixed layer, and to reflect the net effects of input and cycling of these elements in the overlying mixed layer. Labile and refractory fractions were determined by a two-stage leaching technique. Data showed that water masses downstream of the islands were enriched in total iron and aluminium (0.25–2.68 nmol L− 1 and 0.34–3.28 nmol L− 1 respectively), relative to the southern HNLC control sites (0.15–0.29 nmol L− 1 for Fe and 0.12–0.29 nmol L− 1 for Al), with only a small fraction (typically < 1%) being acid leachable in both environments. Particulate iron predominantly derived from the island system represents a significant fraction of the total water column iron inventory and may complement dissolved Fe inputs that help support the high summer productivity around the Crozet islands.  相似文献   

3.
Microzooplankton (heterotrophic microplankton and heterotrophic nanoflagellates) and their herbivorous activity were estimated from dilution experiments in August 1998 during two Lagrangian drift experiments that sampled contrasting conditions—an upwelling/relaxation event along the shelf edge and an oligotrophic offshore filament. During upwelling/relaxation, heterotrophic microplankton were present at mean surface concentrations between 15,000 and 48,000 cells l−1. Heterotrophic nanoflagellate concentrations were between 200 and 700 cells ml−1 and the most abundant component of the heterotrophic microplankton was the aloricate choreotrich ciliates which increased dramatically in concentration from 6,000 to 24,000 cells l−1 during the first 4 days of the study. Total microzooplankton biomass reached a maximum of 39mgC.m−3. In the filament, which developed from the upwelling, cell concentrations were lower and averaged 4,500 cells l−1 for heterotrophic microplankton and 250 cells ml−1 for heterotrophic nanoflagellates. Total microzooplankton biomass was about 10–12mgC.m−3. Microzooplankton turned over between 40 and 85% of the phytoplankton standing stock, thereby consuming between 5 and 78mg phytoplankton carbon.m−3.d−1. The magnitude of this activity was highest during upwelling/relaxation and was positively correlated to heterotrophic nanoflagellate biomass and chlorophyll-a concentration but not heterotrophic microplankton biomass. The proportion of primary production grazed decreased from 160 to 59% d−1 during upwelling/relaxation and ranged between 60 and 90% d−1 in the filament. Microzooplankton herbivory within the euphotic zone increased from 684 to >2000mgC.m−2.d−1 during upwelling/relaxation and was between 327 and 802mgC.m−2.d−1 in the filament. Although microzooplankton herbivory was lower and less variable during the filament study, microzooplankton consumed on average 60% of the phytoplankton standing stocks which was higher than found during upwelling/relaxation. Microzooplankton assimilation efficiency ranged between 3 and 33% during upwelling/relaxation and between 0 and 13% in the filament. Our data demonstrate a close coupling between phytoplankton growth and microzooplankton herbivory in surface waters off the Galician Coast and suggest that microzooplankton may have been a significant sink for phytogenic carbon during August 1998.  相似文献   

4.
Dissolved iodate and total iodine were studied in St Helena Bay, South Africa, during a period of acute hypoxia, following upwelling off Cape Columbine. Despite the generally high concentrations of chlorophyll α (10–30 mg m−3) total iodine concentration was essentially constant in the main part of the Bay, and similar to that found elsewhere in the oceans. Occasional, lower concentrations of total iodine (0·28 to 0·42 μM) were found with exceptionally high chlorophyll α concentrations (500 mg m−3) in shallow waters. In contrast, iodate was found to be reduced to iodide at both the surface and the bottom of the Bay. The implications of these changes are discussed, given that the surface waters reflect sustained eutrophication while the bottom waters are hypoxic as a result of the organic-rich sediment from the waters above.  相似文献   

5.
Copper concentrations have been measured in more than 200 samples collected from an Alaskan fjord and continental shelf and slope regions in the northwestern Gulf of Alaska. Concentrations were lowest (2·1 nmol kg−1) at depths of 400–1000 m in the continental slope waters of the Gulf of Alaska. Copper increased systematically with decreasing salinities shoreward to concentrations >30 nmol kg−1 in fjord surface waters during summer months of high freshwater runoff. Copper concentrations increased with depth at an inner fjord station where deep basin waters have restricted circulation, and these data together with surface (<5 cm) pore water copper concentrations (mean=122 nmol kg−1) about an order of magnitude higher than bottom water copper concentrations are indicative of a flux of copper across the sediment-seawater interface. This latter was estimated at 32±12 nmol cm−2 annually, and represented less than 20% of the annual input to fjord surface water (228–411 nmol cm−2) added during summer months. Mass balances in bottom waters indicate a vigorous recycling of copper with a residence time estimated at 21±11 days. Most copper that is remobilized in surface sediments is returned to bottom waters and little (3%) is removed by subsequent diagenetic reaction in the buried sediments. However, an estimate of copper accumulating in anoxic fjord sediments was comparable with copper added to fjord surface waters suggesting that input-removal reactions rather than internal cycling controls copper geochemistry in this estuary.  相似文献   

6.
A five-element mooring array is used to study surface boundary-layer transport over the Northern California shelf from May to August 2001. In this region, upwelling favorable winds increase in strength offshore, leading to a strong positive wind stress curl. We examine the cross-shelf variation in surface Ekman transport calculated from the wind stress and the actual surface boundary-layer transport estimated from oceanic observations. The two quantities are highly correlated with a regression slope near one. Both the Ekman transport and surface boundary layer transport imply curl-driven upwelling rates of about 3×10−4 m s−1 between the 40 and 90 m isobaths (1.5 and 11.0 km from the coast, respectively) and curl-driven upwelling rates about 1.5×10−4m s−1 between the 90 and 130 m isobaths (11.0 and 28.4 km from the coast, respectively). Thus curl-driven upwelling extends to at least 25 km from the coast. In contrast, upwelling driven by the adjustment to the coastal boundary condition occurs primarily inshore of the 40-m isobath. The upwelling rates implied by the differentiating the 40-m transport observations with the coastal boundary condition are up to 8×10−4 m s−1. The estimated upwelling rates and the temperature–nitrate relationship imply curl-driven vertical nitrate flux divergences are about half of those driven by coastal boundary upwelling.  相似文献   

7.
Dissolved and total dissolvable manganese concentrations have been measured at four stations in the western North Atlantic Ocean. Total dissolvable manganese concentrations are high in surface waters, decrease to uniformly low levels throughout the bulk of the water column, and increase in the bottom nepheloid layer. Dissolved Mn (Mnd) concentrations follow the total dissolvable concentrations throughout the surface and deep waters but do not increase in the near-bottom waters.Deep water concentrations of Mnd decrease from 30 ng l?1 in the Newfoundland Basin to 20 ng l?1 in the Sargasso Sea. This change and other features of the deep water distribution of dissolved manganese could be associated with the slow oxidation of Mn2+ to MnO2. There is also evidence at one station of scavenging of manganese from the dissolved phase in the near-bottom layer which may again be related to the kinetics of manganese oxidation.  相似文献   

8.
Data presented in this paper are part of an extensive investigation of the physics of cross-shelf water mass exchange in the north-east of New Zealand and its effect on biological processes. Levels of dissolved dimethylsulfide (DMS) were quantified in relation to physical processes and phytoplankton biomass. Measurements were made at three main sites over the north-east continental shelf of New Zealand's North Island during a current-driven upwelling event in late spring 1996 (October) and an oceanic surface water intrusion event in summer 1997 (January). DMS concentrations in the euphotic zone ranged between 0.4 and 12.9 nmol dm−3. Integrated water column DMS concentrations ranged from 33 to 173 μmol m−2 in late spring during the higher biomass (15–62 Chl-a mg m−2) month of October, and from 25 to 38 μmol m−2 in summer during the generally lower biomass (16–42 Chl-a mg m−2) month of January. We observed high levels of DMS in the surface waters at an Inner Shelf site in association with a Noctiluca scintillans bloom which is likely to have enhanced lysis of DMSP-producing algal cells during phagotrophy. Integrated DMS concentrations increased three-fold at a Mid Shelf site over a period of a week in conjunction with a doubling of algal biomass. A high correlation (r2=0.911, significant <0.001) of integrated DMS and chlorophyll-a concentrations for compiled data from all stations indicated that chlorophyll-a biomass may be a reasonable predictor of DMS in this region, even under highly variable hydrographic conditions. Integrated bacterial production was inversely correlated to DMS production, indicating active bacterial consumption of DMS and/or its precursor.  相似文献   

9.
Surface transects and vertical profiles of macronutrients, dissolved iron (D-Fe), and dissolved manganese (D-Mn) were investigated during August 2003 in the southeastern Bering Sea. We observed iron-limited, HNLC surface waters in the deep basin of the Bering Sea (15-20 μmol/kg nitrate, ∼0.07 nmol/kg D-Fe, and ?1.0 nmol/kg D-Mn); nitrate-limited, iron-replete surface waters over the shelf (<0.1 μmol/kg nitrate, 0.5-4 nmol/kg D-Fe, and 2-33 nmol/kg D-Mn); and high biomass at the shelf break (“Green Belt”), where diatoms appeared to have been stressed by low D-Fe concentrations (<0.3 nmol/kg). Sources of nitrate and iron to the Green Belt were investigated. A mixture of Aleutian North Slope Current water (with elevated, but non-sufficient iron concentrations relative to its high nitrate concentrations) and surface waters from the vicinity of the Bering Canyon (with lower nitrate concentrations, but similar dissolved iron concentrations) was carried along the shelf break by the Bering Slope Current. This water mixture provided macro- and micronutrients at the southern end of the shelf break. The oceanic domain supplied additional macronutrients to Green Belt waters, while the bottom layer of the outer shelf domain supplied additional macro- and micronutrients through enhanced vertical mixing at the shelf break. Surface waters near the Pribilof Islands, where the highest surface D-Fe concentrations were observed (∼5-6 nmol/kg), represent a potential source of additional iron to Green Belt waters. During summer, the subsurface water of the middle shelf domain is a potential source of nitrate to the nitrate depleted waters of the shelf. In this subsurface cool pool, we observed evidence of substantial denitrification with lower than expected nitrate concentrations.  相似文献   

10.
Vertical profiles of dimethylsulfide (DMS) and β-dimethylsulfoniopropionate, particulate (pDMSP) and dissolved (dDMSP), were measured biweekly in the upper 140 m of the Sargasso Sea (32°10′N, 64°30′W) during 1992 and 1993. DMS and pDMSP showed strong, but different, seasonal patterns; no distinct intra-annual pattern was observed for dDMSP. During winter, concentrations of DMS were generally less than 1 nmol l−1 at all depths, dDMSP was less than 3 nmol l−1 and pDMSP was less than 8 nmol l−1. In spring, concentrations of both dDMSP and pDMSP rose, on a few occasions up to 20 nmol l−1 in the dissolved pool and up to 27 nmol l−1 in the particulate pool. These increases, due to blooms of DMSP-containing phytoplankton, resulted in only minor increases in DMS concentrations (up to 4 nmol l−1). Throughout the summer, the concentrations of DMS continued to increase, reaching a maximum in August of 12 nmol l−1 (at 30 m depth). There was no concomitant summer increase in dDMSP or pDMSP. The differences among the seasonal patterns of DMS, dDMSP, and pDMSP suggest that the physical and biological processes involved in the cycling of DMS change with the seasons. There is a correlation between the concentration of DMS and temperature in this data set, as required by some of the climate feedback models that have been suggested for DMS. A full understanding of the underlying processes controlling DMS is required to determine if the temperature-DMS pattern is of significance in the context of global climate change.  相似文献   

11.
The first oceanographic research (hydrography, nutrient salts, chlorophyll, primary production and phytoplankton assemblages) in a Middle Galician Ria was carried out in Corme-Laxe during 2001, just a year before the Prestige oil spill, being the only reference to evaluate eventual changes in the phytoplankton community. Due to the small size of this ria (6.5 km2), oceanographic processes were driven by the continental water supplied by Anllons River during the wet season (20–30 m3 s−1 in winter), and the strong oceanic influence from the nearby shelf during the dry season. The annual cycle showed a spring bloom with high levels of chlorophyll (up to 14 μg Chl-a L−1) and primary production (3 g C m−2 d−1) and a summer upwelling bloom (up to 8 μg Chl-a L−1 and 10 g C m−2 d−1) where the proximity of the Galician upwelling core (<13.5 °C at sea surface) favors the input of upwelled seawater (up to 9 μM of nitrate and silicate) to the bottom ria layer, even during summer stratification events (primary production around 2 g C m−2 d−1). Thus, phytoplankton assemblages form a “continuum” from spring to autumn with a predominance of diatoms and overlapping species between consecutive periods; only in autumn dinoflagellates and flagellates characterized the phytoplankton community. In the Middle Rias as Corme-Laxe, the nutrient values, Chl-a, primary production and phytoplankton abundance for productive periods were higher than those reported for the Northern (Ria of A Coruña) and Southern Rias (Ria of Arousa) for year 2001; this suggests the importance of the hydrographic events occurring in the zone of maximum upwelling intensity of the Western Iberian Shelf, where a lack of annual cycles studies exists.  相似文献   

12.
Physical forcing plays a major role in determining biological processes in the ocean across the full spectrum of spatial and temporal scales. Variability of biological production in the Bay of Bengal (BoB) based on basin-scale and mesoscale physical processes is presented using hydrographic data collected during the peak summer monsoon in July–August, 2003. Three different and spatially varying physical processes were identified in the upper 300 m: (I) anticyclonic warm gyre offshore in the southern Bay; (II) a cyclonic eddy in the northern Bay; and (III) an upwelling region adjacent to the southern coast. In the warm gyre (>28.8 °C), the low salinity (33.5) surface waters contained low concentrations of nutrients. These warm surface waters extended below the euphotic zone, which resulted in an oligotrophic environment with low surface chlorophyll a (0.12 mg m−3), low surface primary production (2.55 mg C m−3 day−1) and low zooplankton biovolume (0.14 ml m−3). In the cyclonic eddy, the elevated isopycnals raised the nutricline upto the surface (NO3–N > 8.2 μM, PO4–P > 0.8 μM, SiO4–Si > 3.5 μM). Despite the system being highly eutrophic, response in the biological activity was low. In the upwelling zone, although the nutrient concentrations were lower compared to the cyclonic eddy, the surface phytoplankton biomass and production were high (Chl a – 0.25 mg m−3, PP – 9.23 mg C m−3 day−1), and mesozooplankton biovolume (1.12 ml m−3) was rich. Normally in oligotrophic, open ocean ecosystems, primary production is based on ‘regenerated’ nutrients, but during episodic events like eddies the ‘production’ switches over to ‘new production’. The switching over from ‘regenerated production’ to ‘new production’ in the open ocean (cyclonic eddy) and establishment of a new phytoplankton community will take longer than in the coastal system (upwelling). Despite the functioning of a cyclonic eddy and upwelling being divergent (transporting of nutrients from deeper waters to surface), the utilization of nutrients leading to enhanced biological production and its transfer to upper trophic levels in the upwelling region imply that the energy transfer from primary production to secondary production (mesozooplankton) is more efficient than in the cyclonic eddy of the open ocean. The results suggest that basin-scale and mesoscale processes influence the abundance and spatial heterogeneity of plankton populations across a wide spatial scale in the BoB. The multifaceted effects of these physical processes on primary productivity thus play a prominent role in structuring of zooplankton communities and could consecutively affect the recruitment of pelagic fisheries.  相似文献   

13.
Few data on dissolved trace metals in rivers and estuaries are presently available. This paper is an attempt to provide additional data on dissolved concentrations obtained in polluted and so-called unpolluted river estuarine systems. Data for two major French rivers (Gironde, Rhône) have been compared with the Chinese Yellow River (Huanghe) and Yangtze River (Changjiang). Dissolved Cd concentrations have been measured by differential pulse anodic stripping voltammetry. Average concentrations range from 15 ng kg−1 to 50 ng kg−1 (0.13–0.45 nmol kg−1) in the French rivers and are below 4 ng kg−1 (0.040 nmol kg−1) in the Chinese rivers.In all the estuaries studied the dissolved Cd concentrations depict a systematic bulge in the mixing zone which is attributed largely to remobilization processes from particulate matter when the chlorinity increases. Other parameters that may also play a significant role for remobilization are discussed. The processes concerned lead us to reassess the net Cd river input to the oceans, and this should be taken into account for a more precise evaluation of the residence time of oceanic Cd.  相似文献   

14.
The speciation of sedimentary sulfur (pyrite, acid volatile sulfides (AVS), S0, H2S, and sulfate) was analyzed in surface sediments recovered at different water depths from the northwestern margin of the Black Sea. Additionally, dissolved and dithionite-extractable iron were quantified, and the sulfur isotope ratios in pyrite were measured. Sulfur and iron cycling in surface sediments of the northwestern part of the Black Sea is largely influenced by (1) organic matter supply to the sediment, (2) availability of reactive iron compounds and (3) oxygen concentrations in the bottom waters. Biologically active, accumulating sediments just in front of the river deltas were characterized by high AVS contents and a fast depletion of sulfate concentration with depth, most likely due to high sulfate reduction rates (SRR). The δ34S values of pyrite in these sediments were relatively heavy (−8‰ to −21‰ vs. V-CDT). On the central shelf, where benthic mineralization rates are lower, re-oxidation processes may become more important and result in pyrite extremely depleted in δ34S (−39‰ to −46‰ vs. V-CDT). A high variability in δ34S values of pyrite in sediments from the shelf-edge (−6‰ to −46‰ vs. V-CDT) reflects characteristic fluctuations in the oxygen concentrations of bottom waters or varying sediment accumulation rates. During periods of oxic conditions or low sediment accumulation rates, re-oxidation processes became important resulting in low AVS concentrations and light δ34S values. Anoxic conditions in the bottom waters overlying shelf-edge sediments or periods of high accumulation rates are reflected in enhanced AVS contents and heavier sulfur isotope values. The sulfur and iron contents and the light and uniform pyrite isotopic composition (−37‰ to −39‰ vs. V-CDT) of sediments in the permanently anoxic deep sea (1494 m water depth) reflect the formation of pyrite in the upper part of the sulfidic water column and the anoxic surface sediment. The present study demonstrates that pyrite, which is extremely depleted in 34S, can be found in the Black Sea surface sediments that are positioned both above and below the chemocline, despite differences in biogeochemical and microbial controlling factors.  相似文献   

15.
The release of ammonium from the photochemical degradation of dissolved organic matter (DOM) has been proposed by earlier studies as a potentially important remineralisation pathway for refractory organic nitrogen. In this study the photochemical production of ammonium from Baltic Sea DOM was assessed in the laboratory. Filtered samples from the Bothnian Bay, the Gulf of Finland and the Arkona Sea were exposed to UVA light at environmentally relevant levels, and the developments in ammonium concentrations, light absorption, fluorescence and molecular size distribution were followed. The exposures resulted in a decrease in DOM absorption and loss of the larger sized fraction of DOM. Analysis of the fluorescence properties of DOM using parallel factor analysis (PARAFAC) identified 6 independent components. Five components decreased in intensity as a result of the UVA exposures. One component was produced as a result of the exposures and represents labile photoproducts derived from terrestrial DOM. The characteristics of DOM in samples from the Bothnian Bay and Gulf of Finland were similar and dominated by terrestrially derived material. The DOM from the Arkona Sea was more autochthonous in character. Photoammonification differed depending on the composition of DOM. Calculated photoammonification rates in surface waters varied between 121 and 382 μmol NH4+ L− 1 d− 1. Estimated areal daily production rates ranged between 37 and 237 μmol NH4+ m− 2 d− 1, which are comparable to atmospheric deposition rates and suggest that photochemical remineralisation of organic nitrogen may be a significant source of bioavailable nitrogen to surface waters during summer months with high irradiance and low inorganic nitrogen concentrations.  相似文献   

16.
Lagrangian experiments with short-term, drifting sediment traps were conducted during a cruise on RRS Charles Darwin to the NW coast of Spain to study the vertical flux and composition of settling biogenic matter. The cruise was split into two legs corresponding to (i) a period of increased production following an upwelling event on the continental shelf (3–10 August 1998) and (ii) an evolution of a cold water filament originating from the upwelled water off the shelf (14–19 August). The export of particulate organic carbon (POC) from the upper layer (0–60m) on the shelf was 90–240mgC.m−2.d−1 and off the shelf was 60–180mgC.m−2.d−1. Off shelf the POC flux at 200m was 50–60mg.m−2.d−1. A modest sedimentation of diatoms (15–30mgC.m−2.d−1) after the upwelling was associated with increased vertical flux of chlorophyll a (1.8–2.1mg.m−2.d−1) and a decrease of the POC:PON molar ratio of the settled material from 9 to 6.4. Most of the pico-, nano-, and microplankton in the settled material were flagellates; diatoms were significant during the on shelf and dinoflagellates during the off shelf leg. Off shelf, the exponential attenuation of POC flux indicated a strong retention capacity of the plankton community between 40 and 75m. POC:PON ratio of the settled particulate matter decreased with depth and the relative portion of flagellates increased, suggesting a novel, flagellate and aggregate mediated particulate flux in these waters. Export of POC from the euphotic layer comprised 14–26% of the integrated primary production per day during the on shelf leg and 25–42% during the off shelf leg, which characterises the importance of sedimentation in the organic carbon budget of these waters.  相似文献   

17.
A sensitive method for iron determination in seawater has been adapted on a submersible chemical analyser for in situ measurements. The technique is based on flow injection analysis (FIA) coupled with spectrophotometric detection. When direct injection of seawater was used, the detection limit was 1.6 nM, and the precision 7%, for a triplicate injection of a 4 nM standard. At low iron concentrations, on line preconcentration using a column filled with 8-hydroxyquinoline (8HQ) resin was used. The detection limit was 0.15 nM (time of preconcentration = 240 s), and the precision 6%, for a triplicate determination of a 1 nM standard, allowing the determination of Fe in most of the oceanic regimes, except the most depleted surface waters. The effect of temperature, pressure, salinity, copper, manganese, and iron speciation on the response of the analyser was investigated. The slope of the calibration curves followed a linear relation as a function of pressure (Cp = 2.8 × 10− 5P + 3.4 × 10− 2 s nmol− 1, R2 = 0.997, for Θ = 13 °C) and an exponential relation as a function of temperature (CΘ = 0.009e0.103Θ, R2 = 0.832, for P = 3 bar). No statistical difference at 95% confidence level was observed for samples of different salinities (S = 0, 20, 35). Only very high concentration of copper (1000 × [Fe]) produced a detectable interference. The chemical analyser was deployed in the coastal environment of the Bay of Brest to investigate the effect of iron speciation on the response of the analyser. Direct injection was used and seawater samples were acidified on line for 80 s. Dissolved iron (DFe, filtered seawater (0.4 μm), acidified and stored at pH 1.8) corresponded to 29 ± 4% of Fea (unfiltered seawater, acidified in line at pH 1.8 for 80 s). Most of Fea (71 ± 4%) was probably a fraction of total dissolvable iron (TDFe, unfiltered seawater, acidified and stored at pH 1.8).  相似文献   

18.
Over 50 seawater samples from two different sites—Barcelona (Spain) and Banyuls-sur-Mer (France)—were analyzed in order to study the extent and postulate the processes driving the enrichment of hydrophobic organic pollutants in the sea surface microlayer (SML). A number of individual polychlorinated biphenyl (PCB) congeners (41) were measured to study their partitioning between the particulate (fraction > 0.7 μm) and the dissolved + colloidal phases (fraction < 0.7 μm), with the latter being differentiated into estimated dissolved and colloidal phases. In addition, several organochlorine pesticides were also measured, namely, HCB, α-HCH, γ-HCH, 4,4′-DDE, 4,4′-DDD and 4,4′-DDT. The presence of PCB congener profiles found in the SML suggests a dynamic coupling with the atmosphere in Banyuls sampling site, whereas offshore Barcelona the presence of highly chlorinated congeners was due to persistent sediment resuspension. The average PCB concentration in the SML dissolved + colloidal phase were higher in Banyuls (7.8 ng L− 1) than in Barcelona (3.6 ng L− 1) samples, but in the particulate phase concentrations were higher in Barcelona (3.2 ng L− 1) to that of Banyuls (1.4 ng L− 1). However, PCB concentrations in the SML generally also showed large variability. Enrichment factors of PCBs and other organochlorine compounds in the SML with respect to the underlying water column ranged from 0.2 to 7.4. This may be explained for both the dissolved + colloidal and particulate phases by the enrichment in the SML of organic carbon (OC) as discerned from particle–water and colloid–water partitioning.  相似文献   

19.
The consequences of two upwelling events in mid- (MW) and late (LW) winter on biogeochemical and phytoplankton patterns were studied in the Pontevedra Ria and compared with the patterns measured under typical winter conditions and under a summer upwelling event. Thermohaline patterns measured during the mid-winter upwelling event (MW-up) revealed the intrusion of saltier seawater (35.9) into the ria associated with the Iberian Poleward Current (IPC). During the late-winter upwelling event (LW-up), the seawater which had welled up into the ria showed characteristics of the Eastern North Atlantic Central Water mass (ENACW). In both cases the measured water residence time (4 days during MW-up and 10 days during LW-up) was related to both meteorological and fluvial forcing. This residence time contrasts with that of summer upwelling (7 days) and with that estimated under unfavorable upwelling atmospheric conditions (2–4 weeks). During MW-up, the ria became poor in nutrients due to continental freshwater dilution, associated with the shorter residence time of the water, and the intrusion of IPC, which is a water body poor in nutrient salts: 2.9 μM of nitrate, 0.1 μM of phosphate and 1.5 μM of silicate. During this event, the ria exported 3.4 molDIN s−1, compared with 6.9 molDIN s−1 in non-upwelling conditions. Phytoplankton showed a uniform distribution throughout the ria, as during unfavorable upwelling conditions, and was characterized by the dominance of diatoms, mainly Nitzschia longissima and Skeletonema costatum. During LW-up, a nutrient depletion in the photic layer also occurred, but as a result of a phytoplankton spring bloom developing at this time. The ria was a nutrient trap where 4.1 molDIN s−1 were processed by photosynthesis. This budget is three times higher than the one under non-upwelling conditions. In contrast with the MW-up, which had no effect on primary production, during LW-up the ria became more productive, although not as productive as during a summer upwelling event (9.9 molDIN s−1). The taxonomic composition of the phytoplankton community did not change noticeably during LW-up and the summer upwelling, with the same species present and changing only in relative proportions. Diatoms were always the dominant microphytoplankton community, with Pseudonitzschia pungens, Thalassionema nitzschioides and several species of Chaetoceros as characteristic taxons.  相似文献   

20.
Dissolved Fe, Mn and Al concentrations (dFe, dMn and dAl hereafter) in surface waters and the water column of the Northeast Atlantic and the European continental shelf are reported. Following an episode of enhanced Saharan dust inputs over the Northeast Atlantic Ocean prior and during the cruise in March 1998, surface concentrations were enhanced up to 4 nmol L− 1 dFe, 3 nmol L− 1 dMn and 40 nmol L− 1 dAl and returned to 0.6 nmol L− 1 dFe, 0.5 nmol L− 1 dMn and 10 nmol L− 1 dAl towards the end of the cruise three weeks later. A simple steady state model (MADCOW, [Measures, C.I., Brown, E.T., 1996. Estimating dust input to the Atlantic Ocean using surface water aluminium concentrations. In: Guerzoni. S. and Chester. R. (Eds.), The impact of desert dust across the Mediterranean, Kluwer Academic Publishers, The Netherlands, pp. 301–311.]) was used which relies on surface ocean dAl as a proxy for atmospheric deposition of mineral dust. We estimated dust input at 1.8 g m− 2 yr− 1 (range 1.0–2.9 g m− 2 yr− 1) and fluxes of dFe, dMn and dAl were inferred. Mixed layer steady state residence times for dissolved metals were estimated at 1.3 yr for dFe (range 0.3–2.9 yr) and 1.9 yr for dMn (range 1.0–3.8 yr). The dFe residence time may have been overestimated and it is shown that 0.2–0.4 yr is probably more realistic. Using vertical dFe versus Apparent Oxygen Utilization (AOU) relationships as well as a biogeochemical two end member mixing model, regenerative Fe:C ratios were estimated respectively to be 20 ± 6 and 22 ± 5 μmol Fe:mol C. Combining the atmospheric flux of dFe to the upper water column with the latter Fe:C ratio, a ‘new iron’ supported primary productivity of only 15% (range 7%–56%) was deduced. This would imply that 85% (range 44–93%) of primary productivity could be supported by regenerated dFe. The open ocean surface data suggest that the continental shelf is probably not a major source of dissolved metals to the surface of the adjacent open ocean. Continental shelf concentrations of dMn, dFe, and to a lesser extent dAl, were well correlated with salinity and express mixing of a fresher continental end member with Atlantic Ocean water flowing onto the shelf. This means probably that diffusive benthic fluxes did not play a major role at the time of the cruise.  相似文献   

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