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1.
In this study we estimate diffusive nutrient fluxes in the northern region of Cape Ghir upwelling system (Northwest Africa) during autumn 2010. The contribution of two co-existing vertical mixing processes (turbulence and salt fingers) is estimated through micro- and fine-structure scale observations. The boundary between coastal upwelling and open ocean waters becomes apparent when nitrate is used as a tracer. Below the mixed layer (56.15±15.56 m), the water column is favorable to the occurrence of a salt finger regime. Vertical eddy diffusivity for salt (Ks) at the reference layer (57.86±8.51 m, CI 95%) was 3×10−5 (±1.89×10−9, CI 95%) m2 s−1. Average diapycnal fluxes indicate that there was a deficit in phosphate supply to the surface layer (6.61×10−4 mmol m−2 d−1), while these fluxes were 0.09 and 0.03 mmol m−2 d−1 for nitrate and silicate, respectively. There is a need to conduct more studies to obtain accurate estimations of vertical eddy diffusivity and nutrient supply in complex transitional zones, like Cape Ghir. This will provide us with information about salt and nutrients exchange in onshore–offshore zones. 相似文献
2.
《Marine Chemistry》2007,103(1-2):30-45
The chemistry of dissolved Fe(III) was studied in the Scheldt estuary (The Netherlands). Two discrete size fractions of the dissolved bulk (< 0.2 μm and < 1 kDa) were considered at three salinities (S = 26, 10 and 0.3).Within the upper estuary, where fresh river water meets seawater, the dissolved Fe concentration decreases steeply with increasing salinity, for the fraction < 0.2 μm from 536 nM at S = 0.3 to 104 nM at S = 10 and for the fraction < 1 kDa from 102 nM to 36 nM Fe. Further downstream, in the middle and lower estuary, this decrease in the Fe concentration continues, but is far less pronounced. For all samples, the traditionally recognised dissolved strong organic Fe-binding ligand concentrations are lower than the dissolved Fe concentrations.Characteristics of dissolved Fe-binding ligands were determined by observing kinetic interactions with adsorptive cathodic stripping voltammetry. From these kinetic experiments we concluded that apart from the well-known strong Fe-binding organic ligands (L, logK′ = 19–22) also weak Fe-binding ligands (P) existed with an α value (binding potential = K′ · [P]) varying between 1011.1 and 1011.9. The presence of this relatively weak ligand explained the high concentrations of labile Fe present in both size fractions in the estuary. This weak ligand can retard or prevent a direct precipitation after an extra input of Fe.The dissociation rate constants of the weak ligand varied between 0.5 × 10− 4 and 4.3 × 10− 4 s− 1. The rate constants of the strong organic ligand varied between kd = 1.5 × 10− 3–17 × 10− 2 s− 1 and kf = 2.2 × 108–2.7 × 109 M− 1 s− 1. The dissociation rate constant of freshly amorphous Fe-hydroxide was found to be between 4.3 × 10− 4 and 3.7 × 10− 3 s− 1, more labile or equal to the values found by Rose and Waite [Rose, A.L., Waite, T.D., 2003a. Kinetics of hydrolysis and precipitation of ferric iron in seawater. Environ. Sci. Technol., 37, 3897–3903.] for freshly precipitated Fe in seawater.Kinetic rate constants of Fe with the ligand TAC (2-(2-Thiazolylazo)-p-cresol) were also determined. The formation rate constant of Fe(TAC)2 varied between 0.1 × 108 and 3.6 × 108 M− 1 s− 1, the dissociation rate constant between 0.2 × 10− 5 and 17 × 10− 5 s− 1 for both S = 26 and S = 10. The conditional stability constant of Fe(TAC)2 (βFe(TAC)2′) varied between 22 and 23.4 for S = 10 and S = 26 more or less equal to that known from the literature (logβFe(TAC)2′ = 22.4; [Croot, P.L., Johansson, M., 2000. Determination of iron speciation by cathodic stripping voltammetry in seawater using the competing ligand 2-(2-Thiazolylazo)-p-cresol (TAC). Electroanalysis, 12, 565–576.]). However, at S = 0.3 the logβFe(TAC)2′ was 25.3, three orders of magnitude higher. Apparently the application of TAC to samples of low salinity can only be done when the correct βFe(TAC)2′ is known. 相似文献
3.
The European flounder Platichthys flesus is a widely distributed epibenthic species and an important component of demersal fish assemblages in the European Atlantic coastal waters. In Portuguese estuaries, this species reaches high densities, especially in Minho estuary (NW Iberian Peninsula, Europe), potentially playing an important role in the system's ecology. In this context, the population structure, production and the habitat use of juvenile P. flesus were investigated. Sampling took place monthly, from February 2009 until July 2010 along the entire estuarine gradient (5 sampling stations distributed in the first 29 km from the river mouth, with S1 located near the river mouth, S2 inside a salt marsh, S3 in a salinity transition zone, while S4 and S5 were located in the upper estuary). Flounder's density varied significantly among sampling stations and seasons (two-way PERMANOVA: p < 0.001), with the majority of the individuals being found during the spring (30.1%) and in S3 and S4 (72.6%). Males and females presented an even distribution, with a higher proportion of males observed during summer. Fish length also differed among sampling stations and seasons (two-way PERMANOVA: p < 0.001), with larger fishes being found in S1 during the autumn (168.50 ± 59.50 mm) and the smallest in S4 during the spring (33.80 ± 3.12 mm). Size classes associated differently with environmental variables, with larger juveniles being more abundant in the downstream areas of the estuary, whereas smaller juveniles were related to higher water temperatures, suggesting a habitat segregation of P. flesus of different sizes. The fish condition of P. flesus in Minho estuary was higher than in other systems, probably due to the dominance of juveniles on the population. Also, the densities found in this estuary were up to 32 times higher than in other locations, suggesting that Minho estuary is an important nursery area for the species. The estimated secondary production of P. flesus was lower than previous studies acknowledged in the system (0.037 g.WWm− 2.year− 1), indicating that the production estimates of this species in estuaries can vary considerably depending on of several factors such as the sampling year and strategy, population and fish size. 相似文献
4.
Investigations of primary production (PP) were undertaken in the southern Benguela ecosystem during two research surveys in October 2006 and May 2007. Significant differences in environmental conditions, as well as biomass and PP, were observed between October and May. During October, integrated biomass and PP were significantly higher, ranging from 20.43 to 355.01 mg m−2, and 0.71 to 6.98 g C m−2 d−1, respectively, than in May, where the range was 47.92–141.79 mg m−2, and 0.70–3.35 g C m−2 d−1, respectively. Distribution patterns indicated low biomass and PP in newly upwelled water along the coast, higher biomass and PP in the mid-shelf region, while lower values were observed at and beyond the shelf edge. Latitudinal variations showed consistently higher biomass and PP in the St. Helena Bay region compared to biomass and PP south of Cape Town. During both surveys, phytoplankton communities were comprised primarily of diatoms and small flagellates, with no significant differences. Phytoplankton adaptation to environmental variability was characterised by increased PmB and Ek under elevated temperatures and irradiance, while no clear relationships were evident for αB. Generalised Additive Models (GAMs) showed that photosynthetic parameters were all significant predictors of photosynthesis rates (Pz), with PmB being the most important, accounting for 36.97% of the deviance in Pz. However, biomass levels and environmental conditions exerted a much greater influence on Pz, with irradiance explaining the largest proportion (68.24%) of the deviance. Multiple predictor GAMs revealed that 96.26% of the deviance in Pz could be explained by a model which included nitrate, chlorophyll a, and irradiance. 相似文献
5.
《Marine Chemistry》2007,103(1-2):103-111
Particle–water interactions of selected platinum group elements (PGE) have been studied as a function of pH (between 5 and 10), salinity, and concentrations of Cl− and Ca2+. Rhodium(III), Pd(II) and Pt(IV) were added to water samples and sediment suspensions and, following a period of equilibration and subsequent phase separation, filtrates and HCl-digested filters were analysed by ICP-MS. PGE removal from the aqueous phase to the particulate phase appeared to proceed via both coagulation of organic/colloidal associations and adsorption to estuarine sediment particles. In river water, removal of Rh increased and Pt decreased with increasing pH, whereas Pd was not detected in the particulate phase throughout much of the pH range studied. In end-member estuarine water (salinity = 28), removal of Rh and Pt increased with increasing pH, but removal of Pd was relatively insensitive to pH. Conditional particulate-aqueous distribution coefficients, KDs (mL g− 1), were on the order of a few hundred (Pd and Pt) to several thousand (Rh) along the estuarine gradient. Increasing salinity and Cl− concentration were accompanied by an increase in KD for Rh and Pd, and a reduction in KD for Pt, while increasing Ca2+ concentration resulted in an increase in KD for all PGE. Experimental observations were qualitatively interpreted in terms of what is known about the aqueous speciation of PGE. Thus, Rh data were consistent with the adsorption of cationic species of the form: [RhCl6−x(H2O)x]x−3, where x = 0 to 6; although in river water complexation by additional (e.g. organic) ligands may have also occurred. Speciation of Pd was predicted to be dominated by organic complexes under all experimental conditions, consistent with its stabilisation in solution in freshwater and apparent salting out and/or coagulation in the presence of dissolved ions. The presence of hydroxychloride complexes of Pt(IV), whose ligand number (and negative charge) increases with increasing chlorinity, could explain most of the experimental observations for this element. 相似文献
6.
《Estuarine, Coastal and Shelf Science》2007,74(3):449-457
Nutrient inputs associated with coastal population growth threaten the integrity of coastal ecosystems around the globe. In order to assess the threat posed by rapid growth in tourism, we analyzed the nutrient concentrations as well as the δ15N of NO3− and macrophytes to detect wastewater nitrogen (N) at 6 locations along a groundwater-dominated coastal seagrass bed on the Caribbean coast of Mexico. We predicted that locations with greater coastal development would have higher concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (P), as well as δ15N of NO3−, reflecting wastewater sources of N. However, concentrations of NO3− were not significantly different between developed (3.3 ± 5.3 μM NO3−) and undeveloped (1.1 ± 0.7 μM) marine embayments. The most important control on DIN concentration appeared to be mixing of fresh and salt water, with DIN concentrations negatively correlated with salinity. The δ15N of NO3− was elevated at an inland pond (7.0 ± 0.42‰) and a hydrologically-connected tide pool (7.6 ± 0.57‰) approximately 1 km downstream of the pond. The elevated δ15N of NO3− at the pond was paralleled by high δ15N values of Cladophora sp., a ubiquitous green alga (10 ± 1‰). We hypothesize that inputs of nitrogen rich (NO3− > 30 μM) groundwater, characterized by 15N enriched signatures, flow through localized submarine groundwater discharges (SGD) and contribute to the elevated δ15N signatures observed in many benthic macrophytes. However, changes in nitrogen concentrations and isotope values over the salinity gradient suggest that other processes (e.g. denitrification) could also be contributing to the 15N enrichments observed in primary producers. More measurements are needed to determine the relative importance of nitrogen transformation processes as a source of 15N to groundwaters; however, it is clear that continued inputs of anthropogenic N via SGD have the potential to severely impact ecologically and economically valuable seagrass meadows and coral reefs along the Caribbean coast of Mexico. 相似文献
7.
The Mondego estuary fish assemblage was studied for the accumulation of PCBs. Three sampling stations were visited along an estuarine salinity gradient, and, in total, 15 species were collected. Analysis of PCBs revealed no significant differences among the sampling stations, although differences were observed among the fish assemblages. Fish assemblages could be divided into three groups. The first group comprised those with higher concentration (more than 10 ng g− 1, dw), included the species Gobius niger, Sardina pilchardus, Anguilla anguilla, Pomatoschistus microps, Chelidonichthys lucerna and Liza ramada; the second group with medium concentration (5–10 ng g− 1, dw), included the species Pomatoschistus minutus, Dicentrarchus labrax, Atherina presbyter, Chelon labrosus, Diplodus vulgaris, Platichthys flesus and Cilata mustela; and a third group with low concentration (less than 5 ng g− 1, dw), included the species Solea solea and Callionymus lyra. A positive correlation was found between lipid content and PCB concentrations. To evaluate the influence of the residence time of species on the accumulation of PCBs, species were divided into two groups: species that spend more than 3 years in the estuary, and species that spend less than 3 years in the estuary. Species that spend more than 3 years in the estuary presented higher concentrations than species that spend less than 3 years in the estuary. CBs 138 and 153 had higher concentration, and tended to increase with time spent in the estuary. 相似文献
8.
《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(5):1217-1235
The total organic carbon (TOC) and total inorganic carbon (CT) exchange between the Atlantic Ocean and the Mediterranean Sea was studied in the Strait of Gibraltar in September 1997. Samples were taken at eight stations from western and eastern entrances of the Strait and at the middle of the Strait (Tarifa Narrows). TOC was analyzed by a high-temperature catalytic oxidation method, and CT was calculated from alkalinity–pHT pairs and appropriate thermodynamic relationships. The results are used in a two-layer model of water mass exchange through the Strait, which includes the Atlantic inflow, the Mediterranean outflow and the interface layer in between. Our observations show a decrease of TOC and an increase of CT concentrations from the surface to the bottom: 71–132 μM C and 2068–2150 μmol kg−1 in the Surface Atlantic Water, 74–95 μM C and 2119–2148 μmol kg−1 in the North Atlantic Central Water, 63–116 μM C and 2123–2312 μmol kg−1 in the interface layer, and 61–78 μM C and 2307–2325 μmol kg−1 in the Mediterranean waters. However, within the Mediterranean outflow, we found that the concentrations of carbon were higher at the western side of the Strait (75–78 μM C, 2068–2318 μmol kg−1) than at the eastern side (61–69 μM C, 2082–2324 μmol kg−1). This difference is due to the mixing between the Atlantic inflow and the Mediterranean outflow on the west of the Strait, which results in a flux of organic carbon from the inflow to the outflow and an opposite flux of inorganic carbon. We estimate that the TOC input from the Atlantic Ocean to the Mediterranean Sea through the Strait of Gibraltar varies from (0.97±0.8)104 to (1.81±0.90)104 mol C s−1 (0.3×1012 to 0.56×1012 mol C yr−1), while outflow of inorganic carbon ranges from (12.5±0.4)104 to (15.6±0.4)104 mol C s−1 (3.99–4.90×1012 mol C yr−1). The high variability of carbon exchange within the Strait is due to the variability of vertical mixing between inflow and outflow along the Strait. The prevalence of organic carbon inflow and inorganic carbon outflow shows the Mediterranean Sea to be a basin of active remineralization of organic material. 相似文献
9.
Thicklip grey mullet, Chelon labrosus, is an important commercial fish species and has been studied worldwide. However, no recent studies have been made regarding polychlorinated biphenyls (PCBs) in wild C. labrosus. Due to that, the concentration of 13 PCBs congeners was measured in muscles and livers, of males and females, of C. labrosus of different ages, allowing the estimation of PCB bioaccumulation throughout the species lifespan, in the Mondego estuary, a southern European temperate estuary. Male muscle sample concentrations ranged from 32 to 96 ng g− 1 (lipid wt.) and in females from 32 to 62 ng g− 1 (lipid wt.). In male liver sample concentrations ranged from 106 to 158 ng g− 1 (lipid wt.), while female concentrations ranged from 88 to 129 ng g− 1 (lipid wt.). The most abundant congeners presenting higher percentages in all samples were CB 138, 153 and 180. No significant differences were found between the concentrations in both sexes, but muscle and liver PCB concentrations in males tended to increase with age whereas in females concentrations remained stable throughout the species lifespan. Significant differences were found between concentrations in muscle and liver. 相似文献
10.
《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(10-11):1305-1321
Below the sill depth (at about 2400 m) of the Alpha-Mendeleyev ridge complex, the waters of the Canada Basin (CB) of the Arctic Ocean are isolated, with a 14C isolation age of about 500 yr. The potential temperature θ decreases with depth to a minimum θm≈−0.524°C near 2400 m, increases with depth through an approximately 300 m thick transition layer to θh≈−0.514°C, and then remains uniform from about 2700 m to the bottom at 3200–4000 m. The salinity increases monotonically with depth through the deep θm and transition layer from about 34.952 to about 34.956 and then remains uniform in the bottom layer. A striking staircase structure, suggestive of double-diffusive convection, is observed within the transition layer. The staircase structure is observed for about 1000 km across the basin and has been persistent for more than a decade. It is characterized by 2–3 mixed layers (10–60 m thick) separated by 2–16 m thick interfaces. Standard formulae, based on temperature and salinity jumps, suggest a double-diffusive heat flux through the staircase of about 40 mW m−2, consistent with the measured geothermal heat flux of 40–60 mW m−2. This is to be expected for a scenario with no deep-water renewal at present as we also show that changes in the bottom layer are too small to account for more than a small fraction of the geothermal heat flux. On the other hand, the observed interfaces between mixed layers in the staircase are too thick to support the required double-diffusive heat flux, either by molecular conduction or by turbulent mixing, as there is no evidence of sufficiently vigorous overturns within the interfaces. It therefore seems, that while the staircase structure may be maintained by a very weak heat flux, most of the geothermal heat flux is escaping through regions of the basin near lateral boundaries, where the staircase structure is not observed. The vertical eddy diffusivity required in these near-boundary regions is O(10−3) m2 s−1. This implies Thorpe scales of order 10 m. We observe what may be Thorpe scales of this magnitude in boundary-region potential temperature profiles, but cannot tell if they are compensated by salinity. The weak stratification of the transition layer means that the large vertical mixing rate implies a local dissipation rate of only O(10−10) W kg−1, which is not ruled out by plausible energy budgets. In addition, we discuss an alternative scenario of slow, continuous renewal of the CB deep water. In this scenario, we find that some of the geothermal heat flux is required to heat the new water and vertical fluxes through the transition layer are reduced. 相似文献
11.
《Estuarine, Coastal and Shelf Science》2006,66(1-2):323-334
The macrotidal bay of Marennes-Oléron is the most important French site for shellfish production (oysters and mussels); yet the primary productivity of the phytoplankton compartment in this system is not well known. In this study, photosynthetic parameters were determined using 14C incubations of bottom and surface water samples, during fall, winter and summer (2001–2002), along a north–south transect in the bay. Estimates of primary productivity showed that water column primary production is light-limited in the bay and that a BZpI0 type model can be applied. Spatial differences existed in the bay, with a more productive northern zone and less productive river area. With a water column primary production of 185 g C m−2 yr−1, Marennes-Oléron Bay lies in the mean range for phytoplankton primary production capacity among European and North American estuaries. 相似文献
12.
《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(6):781-807
The fluxes of total mass, organic carbon (OC), biogenic opal, calcite (CaCO3) and long-chain C37 alkenones (ΣAlk37) were measured at three water depths (275, 455 and 930 m) in the Cariaco Basin (Venezuela) over three separate annual upwelling cycles (1996–1999) as part of the CARIACO sediment trap time-series. The strength and timing of both the primary and secondary upwelling events in the Cariaco Basin varied significantly during the study period, directly affecting the rates of primary productivity (PP) and the vertical transport of biogenic materials. OC fluxes showed a weak positive correlation (r2=0.3) with PP rates throughout the 3 years of the study. The fluxes of opal, CaCO3 and ΣAlk37 were strongly correlated (0.6<r2<0.8) with those of OC. The major exception was the lower than expected ΣAlk37 fluxes measured during periods of strong upwelling. All sediment trap fluxes were significantly attenuated with depth, consistent with marked losses during vertical transport. Annually, strong upwelling conditions, such as those observed during 1996–1997, led to elevated opal fluxes (e.g., 35 g m−2 yr−1 at 275 m) and diminished ΣAlk37 fluxes (e.g., 5 mg m−2 yr−1 at 275 m). The opposite trends were evident during the year of weakest upwelling (1998–1999), indicating that diatom and haptophyte productivity in the Cariaco Basin are inversely correlated depending on upwelling conditions.The analyses of the Cariaco Basin sediments collected via a gravity core showed that the rates of OC and opal burial (10–12 g m−2 yr−1) over the past 5500 years were generally similar to the average annual water column fluxes measured in the deeper traps (10–14 g m−2 yr−1) over the 1996–1999 study period. CaCO3 burial fluxes (30–40 g m−2 yr−1), on the other hand, were considerably higher than the fluxes measured in the deep traps (∼10 g m−2 yr−1) but comparable to those obtained from the shallowest trap (i.e. 38 g m−2 yr−1 at 275 m). In contrast, the burial rates of ΣAlk37 (0.4–1 mg m−2 yr−1) in Cariaco sediments were significantly lower than the water column fluxes measured at all depths (4–6 mg m−2 yr−1), indicating the large attenuation in the flux of these compounds at the sediment–water interface. The major trend throughout the core was the general decrease in all biogenic fluxes with depth, most likely due to post-depositional in situ degradation. The major exception was the relatively low opal fluxes (∼5 g m−2 yr−1) and elevated ΣAlk37 fluxes (∼2 mg m−2 yr−1) measured in the sedimentary interval corresponding to 1600–2000 yr BP. Such compositions are consistent with a period of low diatom and high haptophyte productivity, which based on the trends observed from the sediment traps, is indicative of low upwelling conditions relative to the modern day. 相似文献
13.
《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(3):403-414
Determinations of the activity of the respiratory electron transport system (ETS), during the FRAM III expedition permit us to estimate oxygen utilization rates (RO2) from the surface to 2000 m under the polar pack ice in the Nansen Basin just north of Svalbard (83°N, 7°E) during April 1981. We found RO2 at in situ temperatures ranging from 20 pM O2 min−1 just below the ice to 0.2 pM O2 min−1 at 2000 m. These rates are low compared to most other ocean regions, but they could decrease particulate organic carbon and nitrogen by 76% and 74%, respectively, over a period of ∼6 months. The RO2 calculations based on measurements made at 0 °C yielded a power function of RO2 vs. depth (Z) of RO2=67Z−0.5534. When this RO2 profile was superimposed on a more recent oxygen utilization rate profile made using the 3He–3H–AOU method (OUR), in the same vicinity of the Nansen Basin during 1987 (OUR=52Z–0.4058, [Zheng, Y., Schlosser, P., Swift, J.W., Jones, E.P., 1997. Oxygen utilization rates in the Nansen Basin, Arctic Ocean: implications for new production. Deep Sea Research I 44, 1923–1943]), the agreement of the two profiles was close. On one hand, this was to be expected because RO2 is the biological basis of OUR, on the other hand, it was a surprise because the methodologies are so different. Nitrate mineralization obtained from ETS activities also compared favorably with calculations based on the data of Zheng et al. [1997. Oxygen utilization rates in the Nansen Basin, Arctic Ocean: implications for new production. Deep Sea Research I 44, 1923–1943]. Chlorophyll ranged from 6 ng L−1 at 5 m to 0.06 ng L−1 at 2000 m. Particulate organic carbon (POC) decreased from 0.93 μM C just below the ice to less than 0.4 μM C at 500 m. Particulate organic nitrogen (PON) was not detectable below 70 m, however in the upper 70 m it ranged from 0.16 to 0.04 μM N. The C/N mass ratio over these depths ranged from 5.8 to 11.3. Annual carbon productivity as calculated to balance the total water column respiration was 27 g C m−2 y−1. The integrated respiration rate between 50 and 4000 m suggests that exported production and carbon flux from the 50 m level was 24 g C m−2 y−1. These are minimal estimates for the southern Nansen Basin because they are based on measurements made at the end of the Arctic winter. 相似文献
14.
《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(8):1320-1334
Whereas diatoms (class Bacillariophyceae) often dominate phytoplankton taxa in the Amazon estuary and shelf, their contribution to phytoplankton dynamics and impacts on regional biogeochemistry are poorly understood further offshore in the western tropical Atlantic Ocean (WTAO). Thus, relative contribution of diatoms to phytoplankton biomass and primary production rates and associated environmental conditions were quantified during three month-long cruises in January–February 2001, July–August 2001, and April–May 2003. The upper water column was sampled at 6 light depths (100%, 50%, 25%, 10%, 1% and 0.1% of surface irradiance) at 64 stations between 3° and 14°N latitude and 41° and 58°W longitude. Each station was categorized as ‘oceanic’ or ‘plumewater’, based on principal component analysis of eight physical, chemical and biological variables. All stations were within the North Brazil Current, and plumewater stations were characterized by shallower mixed layers with lower surface salinities and higher dissolved silicon (dSi) concentrations than oceanic stations. The major finding was a much greater role of diatoms in phytoplankton biomass and productivity at plumewater stations relative to oceanic stations. Mean depth-integrated bSi concentrations at the plumewater and oceanic stations were 14.2 and 3.7 mmol m−2, respectively. Mean depth-integrated SiP rates at the plumewater and oceanic stations were 0.17 and 0.02 mmol m−2 h−1, respectively. Based on ratios of SiP and PP rates, and typical Si:C ratios, diatoms contributed on average 29% of primary productivity at plumewater stations and only 3% of primary productivity at oceanic stations. In contrast, phytoplankton biomass (as chlorophyll a concentrations) and primary production (PP) rates (as 14C uptake rates) integrated over the euphotic zone were not significantly different at plumewater and oceanic stations. Chlorophyll a concentrations ranged from 8.5 to 42.4 mg m−2 and 4.0 to 38.0 mg m−2 and PP rates ranged from 2.2 to 11.2 mmol m−2 h−2 and 1.8 to 10.8 mmol m−2 h−2 at plumewater and oceanic stations, respectively. A conservative estimate of annual integrated SiP in offshore waters of Amazon plume between April and August is 0.59 Tmol Si, based on mean SiP rates in plumewaters and satellite-derived estimates of the area of the Amazon plume. In conclusion, river plumewaters dramatically alter the silicon dynamics of the WTAO, forming extensive diatom-dominated phytoplankton blooms that may contribute significantly to the global Si budget as well as contributing to energy and matter flow off of the continental shelf. 相似文献
15.
《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(6):971-986
Biochemical and productivity measurements and nutrient enrichment experiments were conducted on three cruises in summer and two cruises in winter on the shelf and the basin of the northern South China Sea (SCS) between 2001 and 2004. Phytoplankton production, in terms of depth-integrated new production (INP) or depth-integrated primary production (IPP), was higher in winter than in summer and on the shelf than in the basin. In winter, with deepening of the mixed layer, nitrate from the shallow nitracline that characterized the SCS waters was made available in the surface and supported the highest production of the year. Averaged INP measured in winter (0.25 g C m−2 d−1) was about twice the summer average (0.12 g C m−2 d−1) and was 0.19 g C m−2 d−1 on the shelf compared with 0.15 g C m−2 d−1 in the basin. In winter, average INP on the shelf was higher than the basin (0.34 versus 0.21 g C m−2 d−1); whereas in summer, averaged INP on the shelf (0.13 g C m−2 d−1) and the basin (0.11 g C m−2 d−1) were similar. While averaged IPP measured in the basin was higher in winter than in summer (0.53 versus 0.35 g C m−2 d−1), IPP on the shelf showed little temporal variation (0.82 in winter versus 0.84 g C m−2 d−1 in summer). Considerable spatial and inter-annual variation in production was measured in the shelf waters during summer, which could be linked to discharge volume and plume flow direction of the Zhujiang River. While the shelf waters in summer were mostly nitrogen starved or nitrogen and phosphorus co-limited, excessive river runoff may cause the nutritive state to shift to phosphorus deficiency. Waters with low surface salinities and high fluorescence from riverine mixing could be found extending from the Zhujiang mouth to as far as offshore southern Taiwan after a typhoon passed the northern SCS and brought heavy rainfall. Overall, both nutrient advection in winter and river discharge from the China coast in summer made new nitrogen available and shaped the dynamics of phytoplankton production in these oligotrophic waters. 相似文献
16.
《Deep Sea Research Part II: Topical Studies in Oceanography》2010,57(15):1293-1302
As part of a multidisciplinary cruise to the Porcupine Abyssal Plain (PAP) study site (49°00′N 16°30′W), in June and July 2006, observations were made of the vertical nitrate flux due to turbulent mixing. Daily profiles of nitrate and turbulent mixing, at the central PAP site, give a mean nitrate flux into the euphotic zone of 0.09 (95% confidence intervals: 0.05–0.16) mmol N m−2 d−1. This is a factor of 50 lower than the mean observed rate of nitrate uptake within the euphotic zone (5.1±1.3 mmol N m−2 d−1). By using our direct observations to ‘validate’ a previously published parameterisation for turbulent mixing, we further quantify the variability in the vertical turbulent flux across a roughly 100×100 km region centred on the PAP site, using hydrographic data. The flux is uniformly low (0.08±0.26 mmol N m−2 d−1, the large standard deviation being due to a strongly non-Gaussian distribution) and is consistent with direct measurements at the central site. It is demonstrated that on an annual basis convective mixing supplies at least 40-fold more nitrate to the euphotic zone than turbulent mixing at this location. Other processes, such as those related with mesoscale phenomena, may also contribute significantly. 相似文献
17.
An autonomous upwardly-moving microstructure profiler was used to collect measurements of the rate of dissipation of turbulent kinetic energy (ε) in the tropical Indian Ocean during a single diurnal cycle, from about 50 m depth to the sea surface. This dataset is one of only a few to resolve upper ocean ε over a diurnal cycle from below the active mixing layer up to the air–sea interface. Wind speed was weak with an average value of ~5 m s−1 and the wave field was swell-dominated. Within the wind and wave affected surface layer (WWSL), ε values were on the order of 10−7–10−6 W kg−1 at a depth of 0.75 m and when averaged, were almost a factor of two above classical law of the wall theory, possibly indicative of an additional source of energy from the wave field. Below this depth, ε values were closer to wall layer scaling, suggesting that the work of the Reynolds stress on the wind-induced vertical shear was the major source of turbulence within this layer. No evidence of persistent elevated near-surface ε characteristic of wave-breaking conditions was found. Profiles collected during night-time displayed relatively constant ε values at depths between the WWSL and the base of the mixing layer, characteristic of mixing by convective overturning. Within the remnant layer, depth-averaged values of ε started decaying exponentially with an e-folding time of 47 min, about 30 min after the reversal of the total surface net heat flux from oceanic loss to gain. 相似文献
18.
Highly sensitive STOX O2 sensors were used for determination of in situ O2 distribution in the eastern tropical north and south Pacific oxygen minimum zones (ETN/SP OMZs), as well as for laboratory determination of O2 uptake rates of water masses at various depths within these OMZs. Oxygen was generally below the detection limit (few nmol L−1) in the core of both OMZs, suggesting the presence of vast volumes of functionally anoxic waters in the eastern Pacific Ocean. Oxygen was often not detectable in the deep secondary chlorophyll maximum found at some locations, but other secondary maxima contained up to ~0.4 µmol L−1. Directly measured respiration rates were high in surface and subsurface oxic layers of the coastal waters, reaching values up to 85 nmol L−1 O2 h−1. Substantially lower values were found at the depths of the upper oxycline, where values varied from 2 to 33 nmol L−1 O2 h−1. Where secondary chlorophyll maxima were found the rates were higher than in the oxic water just above. Incubation times longer than 20 h, in the all-glass containers, resulted in highly increased respiration rates. Addition of amino acids to the water from the upper oxycline did not lead to a significant initial rise in respiration rate within the first 20 h, indicating that the measurement of respiration rates in oligotrophic Ocean water may not be severely affected by low levels of organic contamination during sampling. Our measurements indicate that aerobic metabolism proceeds efficiently at extremely low oxygen concentrations with apparent half-saturation concentrations (Km values) ranging from about 10 to about 200 nmol L−1. 相似文献
19.
《Estuarine, Coastal and Shelf Science》2005,62(1-2):169-181
Taxonomic composition and productivity of winter and spring phytoplankton in a eutrophic estuary have been investigated in order to elucidate the carbon flux under conditions of limitation by physical factors – light and temperature. In spite of the important differences in nutrients, solar radiation and water temperature between winter and spring season, mean concentrations of particulate organic carbon were equal to 13.2 and 13.0 mgC l−1, respectively. Chlorophyll a averaged at 79 μgChl l−1 in winter, that is 69% of spring. Although community respiration accounted for only 6–26% of light saturated photosynthesis, integrated net primary production of the 1.2 m deep water column was negative until April. High attenuation of the water body (Ko = 2.9 m−1) lead to a negative carbon balance (net heterotrophy) below 35 cm for all sampling dates. Thus, the high winter POC and phytoplankton values can only originate from summer or autumn primary production. This assumption was supported by a carbon loss rate of just 3% of total organic carbon per day for the whole water column. The composition of phytoplankton was very constant through both seasons: 39% Chlorophyceae, 33% Cyanobacteria and 25% Bacillariophyceae. As expected, phytoplankton was low light acclimated, having high α values (slope of light limited photosynthesis), but moderate maximum photosynthesis rates at saturating irradiances, which were heavily affected by temperature. Calculation of net carbon flux yet showed net heterotrophy of the Bodden waters in winter and early spring were caused by external physical limitation (low surface irradiance and low temperature) in combination with a high light attenuation of the water body. 相似文献
20.
《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(8):1273-1288
The giant diatom Ethmodiscus was examined along an east–west transect at 28–30°N during 2002 and 2003 to determine if abundance, chemical composition or physiological status of this largest of diatoms varied on the scale of 100's–1000's of km in North Pacific gyre. Abundance ranged from <0.1–>2.0 cells m−3 and supported the notion of an abundance mosaic reported previously. However, there was only minimal support for the relationship between abundance and nutrient concentration at 125 m reported previously. Cellular chlorophyll varied little along the transect (7.3–10.9 ng chl cell−1) except at the westernmost station. Cellular N and P quotas co-varied 3–4.5 fold (mean=50.8±3.7 and 3.7±0.8 nmol N and P cell−1) and yielded N:P ratios that closely clustered around the Redfield ratio (average=14.6±1.1). Only low levels of chlorophyll-normalized alkaline phosphatase (APase) activity were observed (0.4–2.5 nmol P μg chl−1 h−1) with APase activity lower than that in either the bulk water, or co-occurring Trichodesmium spp. and Pyrocystis noctiluca. The active fluorescence parameter Fv:Fm, a property sensitive to Fe stress, was uniformly high at all stations (average=0.73±0.04 for 2003, and 0.69±0.05 for 2002), indicating sufficient Fe for optimum photosynthetic competence. These results contrasted sharply with results from Rhizosolenia mats reported along the same transect where there was a significant decline westward in Fv:Fm. Both ferredoxin (Fd) and flavodoxin accumulated in cells of Ethmodiscus, resulting in Fd Index values of<0.6. Iron cell quotas ranged from 0.7–5.1 pmol Fe cell−1. When normalized to cytoplasmic volume, the Fe μm−3 was comparable to that of Escherichia coli. We note that the disproportionate contribution of the vacuole (with its high organic content) to total volume typical of large diatoms is a potentially significant source of error in Fe:C ratios and suggest that Fe should be normalized to cytoplasmic volume whenever possible to permit valid intercomparisons between studies. The composition, Fv:Fm data and Fe:C ratio suggest a relatively uniform population experiencing little N, P or Fe stress. The uncoupling of the Fd Index from these measures is consistent with previous findings showing that the expression of flavodoxin can be characterized as an early stress response and that its accumulation is not necessarily correlated with physiological deficit. Ethmodiscus appears to be well adapted to some of the most oligotrophic waters in the ocean. Because it is an important sedimentary marker, the biology of living Ethmodiscus provides insights into the source of extensive Ethmodiscus oozes. Mass sedimentation after frontal accumulation has been suggested as a source for these oozes. Our data contain no evidence that the flux is linked directly to Fe, N or P stress. 相似文献