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1.
New and published data on the distribution and speciation of manganese and iron in seawater are analyzed to identify and parameterize major biogeochemical processes of their cycling within the suboxic (15.6σt16.2) and anoxic layers (σt16.2) of the Black Sea. A steady-state transport-reaction model is applied to reveal layering and parameterize kinetics of redox and dissolution/precipitation processes. Previously published data on speciation of these elements in seawater are used to specify the nature of the transformations. Two particulate species of iron (Fe(III) hydroxide and Fe(II) sulfide) are necessary to adequately parameterize the vertical profile of suspended iron, while three particulate species (hydrous Mn(IV) oxide, Mn(II) sulfide, and Mn(II) carbonate) are necessary to describe the profile of suspended manganese. In addition to such processes as mixing and advection, precipitation, sinking, and dissolution of manganese carbonate are found to be essential in maintaining the observed vertical distribution of dissolved Mn(II). These results are used to interpret the observed difference in the form of vertical distribution for dissolved Mn(II) and Fe(II). Redox transformations of iron and manganese are coupled via oxidation of dissolved iron by sinking suspended manganese at σt16.2±0.2 kg m−3. The particulate manganese, necessary for this reaction, is supplied through oxidation of dissolved Mn(II). The best agreement with observations is achieved when nitrate, rather than oxygen, is set to oxidize dissolved Mn(II) in the lower part of the suboxic layer (15.90σt16.2). The results support the idea that, after sulfides of these metals are formed, they sink with particulate organic matter. The sinking rates of the particles and specific rates of individual redox and dissolved-particulate transformations have been estimated by fitting the vertical profile of the net rate.  相似文献   

2.
The dissociation constants (pK1 and pK2) for methionine have been measured in artificial seawater as a function of salinity (S = 5 to 35) and temperature (5 to 45 °C). The seawater pK2 values were lower than the values in NaCl at the same ionic strength while the pK1 values in seawater were lower only at S = 35. In an attempt to understand these differences, we have made measurements of the constants in Na–Mg–Cl solutions at 25 °C. The measured values have been used to determine the formation of Mg2+ complexes and Pitzer interaction parameters for Mg2+ with methionine. The seawater model with the interaction parameters accounts for the differences between the value of pK1 and pK2 between NaCl and seawater. This study demonstrates that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.  相似文献   

3.
Different estimates were used to assess the diversity of the total macrofauna and its major taxonomic groups separately from a broad bathymetric range at a site in the NE Atlantic. In the Goban Spur region, a transect was sampled from the shelf to the abyssal plain over a depth range from 200 to 4500 m and in the Porcupine Sea Bight two stations were sampled (at 3670 m and 4115 m). Species diversity (the number of species per number of individuals) increased with increasing water depth, both when expressed as Hurlbert's E(Sn) and as Shannon's H′log e. The expected number of species in a 100-individual sample E(S100) of total macrofauna increased from 30 on the shelf to 68 on the abyssal plain. Evenness (the proportional abundance of species), estimated with Shannon's J′, also increased with water depth from 0.66 to 0.91, whereas dominance (Simpson's D) decreased from 0.09 to 0.01. Species richness (the number of species per unit of area), however, showed a parabolic pattern with a peak at the upper slope. The largest number of species was found at the slope station at 1425 m (232 species within 0.66 m2). It is argued that species richness is not a synonym of species diversity, but that species richness depends both on species density (which decreases with increasing water depth) and on species diversity. Across the whole bathymetric range (200 to 4500 m) a total of 696 species within 8327 specimens in a total sampled area of 4.12 m2 were counted, yielding mean values of 12 individuals per species and 169 species per m2. Different communities were found to exist on the shelf, slope and abyss. It is suggested that this could have been caused by different selection processes. Differences in life-history strategies and organic-matter supply could (at least partly) explain the different community structures and diversity patterns found along the depth gradient.  相似文献   

4.
The Darwin Mounds are a series of small (5 m high, 75–100 m diameter) sandy features located in the northern Rockall Trough. They provide a habitat for communities of Lophelia pertusa and associated fauna. Suspended particulate organic matter (sPOM) reaching the deep-sea floor, which could potentially fuel this deep-water coral (DWC) ecosystem, was collected during summer 2000. This was relatively “fresh” (i.e. dominated by labile lipids such as polyunsaturated fatty acids) and was derived largely from phytoplankton remains and faecal pellets, with contributions from bacteria and microzooplankton. Labile sPOM components were enriched in the benthic boundary layer (10 m above bottom (mab)) relative to 150 mab. The action of certain benthic fauna that are exclusively associated with the DWC ecosystem (e.g. echiuran worms) leads to the subduction of fresh organic material into the sediments. The mound surface sediments are enriched in organic carbon, relative to off-mound sites. There is no evidence for hydrocarbon venting at this location.  相似文献   

5.
The dissociation constants (pK1, pK2 and pK3) for cysteine have been measured in seawater as a function of temperature (5 to 45 °C) and salinity (S = 5 to 35). The seawater values were lower than the values in NaCl at the same ionic strength. In an attempt to understand these differences, we have made measurements of the constants in Na–Mg–Cl solutions at 25 °C. The measured values have been compared to those calculated from the Pitzer ionic interaction model. The lower values of pK3 in the Na–Mg–Cl solutions have been attributed to the formation of Mg2+ complexes with Cys2− anions
Mg2+ + Cys2− = MgCys
The stability constants have been fitted to
after corrections are made for the interaction of Mg2+ with H+.The pK1 seawater measurements indicate that H3Cys+ interacts with SO42−. The Pitzer parameters β0(H3CysSO4), β1(H3CysSO4) and C(H3CysSO4) have been determined for this interaction. The formation of CaCys as well as MgCys are needed to account for the values of pK2 and pK3 in seawater.The consideration of the formation of MgCys and CaCys in seawater yields model calculated values of pK1, pK2 and pK3 that agree with the measured values to within the experimental error of the measurements. This study shows that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.  相似文献   

6.
Jingfeng Wu   《Marine Chemistry》2007,103(3-4):370-381
A low-blank pre-concentration procedure is described for the analysis of picomolar iron (Fe) in seawater by isotope dilution high-resolution inductively coupled plasma mass-spectrometry (HR-ICPMS). The procedure uses a two-step Mg(OH)2 co-precipitation procedure to extract Fe from a 50 ml seawater sample into a 100 μl 4% nitric acid (HNO3) solution followed by HR-ICPMS measurement. The high pre-concentration ratio ( 500:1) achieved by the procedure minimizes the Fe blank due to ICPMS instrumental Fe background and results in a detection limit of  2 pM and a precision of  4% at the 50 pM Fe level. The measurement of a low-Fe seawater sample spiked with gravimetric Fe standard shows that the method can clearly distinguish 0.01 nM Fe from 0.02 nM Fe in seawater with high accuracy. The method is demonstrated by the analysis of dissolved Fe in the equatorial Pacific Ocean.  相似文献   

7.
The unsteady cavity patterns around the gap of the conventional and newly developed semi-spade rudders for marine ships are visualized qualitatively using a high-speed CCD camera. Time-resolved PIV analysis is also performed with the bubble tracers to study the flow behavior over the rudder surface. In addition, pressure measurements are conducted on the rudder surface and inside the gap to find out the flow characteristics around the gap entrance of the rudder. Both the rudders are tested without a propeller wake at the various cavitation numbers and at the rudder deflection angle of −8°θ10°. The strong cavitation patterns around the conventional rudder gap are significantly reduced by adopting a newly developed entrance profile, and a time-resolved velocity field is found to be very effective in catching the vortical cavity flow around the rudder gap. The stagnation point near the gap entrance of the conventional rudder can cause unsteady cavity flow. However, the developed rudder has very stable pressure distribution along the horn surface and decreases the pressure inside the gap because of the modification of the gap entrance. The pressure distribution around the gap of the suction side is closely related to the variation of the rudder deflection angle. The cavitation inception speed is delayed by about 4 knots in the angle range of −5°θ5° by employing the developed profile of the gap entrance.  相似文献   

8.
From observations of ice cover, temperature, salinity, currents and nitrate, it is evident that along-shelf variability was significant over the middle shelf of the eastern Bering Sea, but less distinct than that observed in the cross-shelf domains. Along the 70-m isobath, three zones were evident in the summer: the southeastern cold pool (centered at 57°N); an intermediate zone, consisting of warmer water, with weaker stratification; and the northern cold pool, extending northward from 58°N. Small-scale (20 km) horizontal features that persisted for months were common. Nutrient concentrations were related to salinity and were replenished more uniformly over the southern shelf, than north of the Pribilof Islands. Although mean currents were weak (1 cm s−1), short energetic advective events impacted the temperature and salinity structure.  相似文献   

9.
The spatial distributions of dissolved manganese and nutrients were examined in the Columbia River plume off Oregon and Washington during the summer of 2004 and 2005 as part of the River Influence on Shelf Ecosystems (RISE) program. Factors influencing the hydrochemical characteristics of the freshly formed and aged Columbia River plume were investigated. Hydrographic data and nutrient concentrations were used to delineate three distinct water sources for the Columbia River Plume: California Current surface water, coastal upwelled water, and Columbia River water. The warm, intermediate salinity, nutrient poor California Current water contains low levels of dissolved manganese (< 5 nM) and silicic acid (< 5 μM), and is depleted in nitrate. The cold, high salinity, nutrient rich, freshly upwelled water is highly variable (2–20 nM) in dissolved manganese and can be as high as  45 μM in silicic acid and  30 μM nitrate. The variable Columbia River has summer temperatures ranging from  13 to 24 °C, high silicic acid concentrations (ranging from  120 to 200 μM), and lower nitrate concentrations (ranging from  2 to 20 μM). During the summer, the concentrations of silicic acid and dissolved manganese can exceed 100 μM and 200 nM, respectively, in near-field Columbia River plumes. These values are markedly greater than those of surface coastal waters (even during upwelling conditions). As the plume advects and mixes, the concentrations of these two constituents remain relatively high within plume waters. The concentrations of dissolved manganese in the near-field plume vary with tidal amplitude, exhibiting much higher concentrations for a given salinity during spring tides than during neap tides. For example, the Columbia River plume at a salinity of 20 has a concentration of dissolved manganese of  240 nM during spring tides, as compared to only  60 nM during low amplitude tides. Silicic acid concentrations in the near-field plume remain relatively constant throughout the tidal month. Calculations indicate there is roughly an equivalent yearly delivery of dissolved manganese and silicic acid to the coastal waters off Oregon and Washington by upwelled waters and by the Columbia River plume.  相似文献   

10.
Dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) measured in deep profiles in the N-E Atlantic and in the N-W Mediterranean in the period 1984–2002 are described. After accurate validation, they show close agreement with those previously published.Classic profiles were obtained, with concentrations decreasing in deep waters. In the Mediterranean and in the Atlantic comparable concentrations were found in the 1500–2000 m waters, 44–46 μmol l−1 DOC, 2.6–2.8 μmol l−1 DON and 0.02–0.03 μmol l−1 DOP. In the surface layers, DOC concentrations were higher, but DON and DOP concentrations lower, in the Mediterranean than in the Atlantic, leading to higher element ratios in the Mediterranean. In autumn, values were, respectively, DOC:DON 17 vs. 14, DOC:DOP 950 vs. 500 and DON:DOP 55 vs. 35. The data suggest an increase in DOC and DON in the North Atlantic Central Water over 15 years, which may be linked to the North Atlantic climatic oscillations.Refractory DOM found in the 1500–2000 m layer exhibited C:N:P ratios of 1570:100:1. The labile+semi-labile (=non-refractory) DOM (nrDOM) pool was computed as DOM in excess of the refractory pool. Its contribution to total DOM above the thermocline in the open sea amounted to 25–35% of DOC, 30–35% of DON, and 60–80% of DOP. Element ratios of the nrDOM varied among stations and were lower than those of refractory DOM, except for C:N in the Mediterranean: nrDOC:nrDON 10–19, nrDOC:nrDOP 160–530 and nrDON:nrDOP 15–38. The specific stoichiometry of DOM in the Mediterranean led us to postulate that overconsumption of carbon is probably a main process in that oligotrophic sea.By coupling non-refractory DOM stoichiometry and relationships between the main DOM elements in the water column, the relative mineralization of C, N and P from DOM was studied. Below the thermocline, the preferential removal of phosphorus with regard to carbon from the semi-labile DOM can be confirmed, but not the preferential removal of nitrogen. In the ocean surface layers, processes depend on the oceanic area and can differ from deep waters, so preferential carbon removal seems more frequent. Bacterial growth efficiency data indicate that bacteria are directly responsible for mineralization of a high proportion of DON and DOP in the deep water.  相似文献   

11.
This study presents a sea-level curve from 9500 to 6500 cal BP for the farfield location of Singapore, on the Sunda Shelf in southeast Asia. The curve is based on more than 50 radiocarbon dates from elevations of +1.43 m to −15.09 m representing sea-level index points in intertidal mangrove and shallow marine sediments deposited by sea-level rise accompanying deglaciation. The results indicate that mean sea level rose rapidly from around −17 m at 9500 cal BP to around −3 m by 8000 cal BP. After this time, the data suggest (but do not unequivocally prove) that the rate of sea-rise slowed for a period of 300–500 years centred on 7700 cal BP, shortly after the cessation of meltwater input to the oceans from the northern hemisphere. Renewed sea-level rise amounting to 3–5 m began around 7400 cal BP and was complete by 7000 cal BP. The existence of an inflection in the rate of sea-level rise, with a slow-down centred on 7700 cal BP, is broadly consistent with other available sea-level curves over this interval and is supported by evidence of stable shorelines and delta initiation elsewhere at this time, as well as evidence of comparatively rapid retreat of the West Antarctic ice sheet beginning around 7500 cal BP. ‘Stepped’ sea-level rise occurring shortly after 7500 cal BP and also earlier during deglaciation may have served to focus significant post-glacial episodes of human maritime/coastal dispersal, into comparatively narrow time intervals.  相似文献   

12.
Sources and discharges of dissolved organic carbon (DOC) from the central Sumatran river Siak were studied. DOC concentrations in the Siak ranged between 560 and 2594 μmol l−1 and peak out after its confluence with the river Mandau. The Mandau drains part of the central Sumatran peatlands and can be characterized as a typical blackwater river due to its high DOC concentration, its dark brown-coloured, acidic water (pH 4.4–4.7) and its low concentration of total suspended matter (12–41 mg l−1). The Mandau supplies about half of the DOC that enters the Siak Estuary where it mixes conservatively with ocean water. The DOC input from the Siak into the ocean was estimated to be 0.3 Tg C yr−1. Extrapolated to entire Indonesia the data suggest a total Indonesian DOC export of 21 Tg yr−1 representing 10% of the global riverine DOC input into the ocean.  相似文献   

13.
The marine microalga Dunaliella salina was used as a model organism in this study. Hydroxyl radicals (OH) were determined using HPLC with sodium benzoate as a probe, and the photochemical activity of marine alga in the formation of OH was confirmed for the first time. Coastal organisms are often exposed to both metal pollution and macronutrient enrichment, and so the effects of algal concentration, exposure time, macronutrient (nitrate and phosphate) additions and metal pollution (5.0 μg/L Pb(II) and 0.1 μg/L methylmercury) on the photoproduction of OH were examined. Photoproduction was increased with increasing algal concentration and with exposure time. It could be increased greatly, with or without the presence of D. salina, by the addition of Pb(II), or Pb(II) and methylmercury, but was decreased by the addition of methylmercury only. Photoproduction of OH was positively correlated with the amount of basic functional groups on the cell's surface and also with the chlorophyll a content per cell. The influence of macronutrient additions on the photoproduction of OH resulted from the photolysis of nitrate and their effects on the photochemical activity of D. salina.  相似文献   

14.
In this paper, a time-dependent dynamic equation for the potential energy anomaly, , is rigorously derived from dynamic equations for potential temperature and salinity, the continuity equation and the equation of state for sea water. The terms locally changing are (A) the -advection, (B) the depth-mean straining, (C) the non-mean straining, (D) the vertical advection, (E) the vertical mixing, (F) surface and bottom density fluxes, (G) inner sources of density e.g. due to absorption of solar radiation and the non-linearity of the equation of state, and (H) horizontal divergence of horizontal turbulent density fluxes. In order to derive the equation in concise form, a vertical velocity (linearly varying with depth) with respect to depth-proportional vertical coordinates had to be defined. The evaluation of the terms in the -equation is then carried out for a one-dimensional tidal straining study and a two-dimensional estuarine circulation study. Comparisons to empirical estimates for these terms are made for the one-dimensional study. It is concluded that the -equation provides a general reference for empirical bulk parameterisations of stratification and mixing processes in estuaries and coastal seas and that it is a tool for complete analysis of the relevant terms from numerical models.  相似文献   

15.
Nutrient and oxygen data collected in the southern Aegean Sea (Cretan Sea) and the straits of the Cretan Arc, during the four seasonal PELAGOS cruises in 1994–1995, are investigated and compared with data collected from 1987 to 1992 within the same area. During the cruises of the PELAGOS Project, nutrient enrichment of the intermediate layers of the Cretan Sea was observed, as a result of intrusion of ‘nutrient-rich, oxygen-poor’ Transition Mediterranean Water (TMW) compensating the Cretan Deep Water (CDW) outflow. TMW occupied the intermediate layers of the entire Cretan Sea. The concentrations of nutrients within this layer were often two times higher than those observed in the same area during previous studies undertaken before 1992 (increase 2.5 μmol/l of nitrate, 0.05 μmol/l of phosphate and 2.5μmol/l of silicate). The decrease of oxygen in this layer is about 0.8ml/l (35 μmol/l). Outflow of CDW occurs principally through the Antikithira and Kassos Straits (the two deeper straits of the Cretan Arc); it results in an increase of oxygen content but a decrease in the nutrient content of water in the deep and bottom layers outside the Cretan Sea. The major mesoscale features in the area have a major influence of the distributions and exchanges of nutrients and oxygen through the straits of the Cretan Arc. The surface and the intermediate layers were richer in nutrients and poorer in oxygen in spring (March 1994), than in autumn (September 1994).  相似文献   

16.
A series of experiments was conducted to evaluate the appropriateness of cross-flow ultrafiltration (CFUF) techniques for the determination of the phase speciation of monomethyl mercury (MeHg) in natural waters. Spiral-wound cartridge (Amicon S1Y1) and Miniplate (Amicon) were evaluated for their nominal molecular weight cut-offs of 1 and 10 kDa, respectively. The ultrafiltration behavior of standard macromolecules showed that the permeation of high molecular weight (HMW) organic macromolecules was not significant when a concentration factor (CF)>15 was used. The retention of low molecular weight (LMW) molecules was significant, especially at a low CF<5, suggesting that the use of a high CF (15) will minimize the retention of LMW molecules. Sorptive losses of MeHg in the solution phase to the 1 kDa membrane were negligible, but MeHg bound to HMW macromolecules was still retained (20%), even with a preconditioned membrane. The mass balance recovery of MeHg during ultrafiltration averaged 101±15% (n=7) and 105±14% (n=5) for the 1 and 10 kDa membranes, respectively. Sample storage over 24 h caused significant coagulation (47%) of the <10 kDa MeHg into the 10 kDa–0.45 μm colloidal or the particulate MeHg pool. The 1 kDa–0.45 μm colloidal MeHg in Galveston Bay and the Trinity River water samples accounted for 40–48% of the filter-passing MeHg, although the most abundant fraction (52–60%) of MeHg was the truly dissolved fraction (<1 kDa). The partition coefficient between the colloidal (1 kDa–0.45 μm) and truly dissolved MeHg (average log KC=5.2) was higher than the partition coefficient based on particle/filter-passing (average log KD=4.6) or particle/truly dissolved MeHg (average log KP=4.8), suggesting that MeHg has stronger affinity for natural colloids than macroparticulate materials (>0.45 μm).  相似文献   

17.
The dissolved organic carbon pool (DOC) is among the largest reservoir of reduced carbon on our planet. The demonstration that DOC polymers remain in assembly/dispersion equilibrium forming microscopic hydrogels has a broad range of critical implications. Previous studies estimate that  10% of DOC could be assembled as gels, yielding values of  7 × 1016 g of organic carbon present as microscopic hotspots of high substrate concentration. This huge mass of reduced carbon emphasizes the need to develop reliable methods to systematically investigate the budget of self-assembled marine gels (SAG), and their role in biogeochemical cycling. However, a quantitative method to measure SAG in seawater has not been available. Here we present the validation of a simple assay to measure the mass of organic carbon assembled as microgels in native seawater. This method is based on the ratio of Chlortetracycline (CTC) fluorescence quenching between Ca bound to non-assembled organic molecules and molecules assembled as microgels. This assay can be readily implemented on board using a low cost fluorometer and provisions to measure TOC.  相似文献   

18.
Methods are described for the rapid (11 min) automated shipboard analysis of dissolved sulfur hexafluoride (SF6) in small volume (200 cm3) seawater samples. Estimated precision for the SF6 measurements is 2% or 0.02 fmol kg−1 (whichever is greater). The method also allows for the simultaneous measurement of chlorofluorocarbon-11 (CFC11) and chlorofluorocarbon-12 (CFC12) on the same water sample, with significantly improved sensitivity over previous analytical methods.  相似文献   

19.
Geochemical estimates of N2 fixation in the North Atlantic often serve as a foundation for estimating global marine diazotrophy. Yet despite being well-studied, estimations of nitrogen fixation rates in this basin vary widely. Here we investigate the variability in published estimates of excess nitrogen accumulation rates in the main thermocline of the subtropical North Atlantic, testing the assumptions and choices made in the analyses. Employing one of these previously described methods, modified here with improved estimates of excess N spatial gradients and ventilation rates of the main thermocline, we determine a total excess N accumulation rate of 7.8 ± 1.7 × 1011 mol N yr− 1. Contributions to excess N development include atmospheric deposition of high N:P nutrients (adding excess N at a rate of 3.0 ± 0.9 × 1011 mol N yr− 1 for  38% of the total), high N:P dissolved organic matter advected into and mineralized in the main thermocline (adding excess N at 2.2 ± 1.1 × 1011 mol N yr− 1 for  28% of the total), and, calculated by mass balance of the excess N field, N2 fixation (adding excess N at 2.6 ± 2.2 × 1011 mol N yr− 1 for  33% of the total). Assuming an N:P of 40 and this rate of excess N accumulation due to the process, N2 fixation in the North Atlantic subtropical gyre is estimated at  4 × 1011 mol N yr− 1. This relatively low rate of N2 fixation suggests that i) the rate of N2 fixation in the North Atlantic is greatly overestimated in some previous analyses, ii) the main thermocline is not the primary repository of N fixed by diazotrophs, and/or iii) the N:P ratio of exported diazotrophic organic matter is much lower than generally assumed. It is this last possibility, and our uncertainty in the N:P ratios of exported material supporting excess N development, that greatly lessens our confidence in geochemical measures of N2 fixation.  相似文献   

20.
The biogeochemistry of the following elements Al, Fe, Sibio, POC, PNtot, Cabio, Sorg, P and Mn has been studied within waters of the Cretan Sea in March and September 1994, as part of the PELAGOS project. Particulate aluminosilicate concentrations, exemplified by Al, are very low (<1 μgl−1) especially in the upper waters. Higher concentrations occur below 200 m, especially at depths of 200 m and 500–700 m in the central and eastern areas, and are thought to result from sediment injections from the shelf edge and slope. The results for Sibio, Cabio, P and Sorg show much higher concentrations within the photic waters. Temporal and spatial high concentrations in these waters closely relate to the existence of cyclonic eddies on the east and west sides of the sea, while low concentrations are associated with an intervening anticyclonic eddy. However in September, discharge of Black Sea Water in the west sufficiently suppresses the thermocline to prevent upwelled water from reaching the surface and hence these substances are prevented from forming.Particulate Fe (expressed as Feexcess) concentrations show much higher concentrations relative to Al in September, and are thought to result from additional atmospheric inputs. The low particulate Mn concentrations in the upper water compared with deeper waters are considered to be a product of photoinhibition of MnOx precipitation from Mn(II).An attempt has been made to assess input/output budgets of Al, Ca, Fe and Mn through the Antikithira and Kassos Straits. Much of the outflows leave through the Kassos Strait and, except for Ca, net outflows through the Antikithira Straits are negligible.  相似文献   

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