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1.
Shear and Richardson number in a mode-water eddy   总被引：1，自引：0，他引：1  
Measurements of stratification and shear were carried out as part of the EDDIES tracer release experiment in mode-water eddy A4 during the summer of 2005. These measurements were accomplished using both shipboard instrumentation and a drifting mooring. A strong relationship between shear intensity and distance from the center of the eddy A4 was observed with the shipboard ADCP. Diapycnal diffusivity at the SF6 tracer isopycnal prior to and during the release was estimated from the drifting mooring to be 2.9×10−6 m2 s−1. Diffusivity increased by an order of magnitude to 3.2×10−5 m2 s−1 during the period of the final tracer survey in early September, which was similar to the value estimated from the tracer analysis for the whole experiment (3.5×10−5 m2 s−1, [Ledwell, J.R., McGillicuddy Jr., D.J., Anderson, L.A., 2008. Nutrient flux into an intense deep chlorophyll layer in a mode-water eddy. Deep-Sea Research II, this issue [doi:10.1016/j.dsr2.2008.02.005]].  相似文献   

2.
The organic matter released by the marine phytoplankton species Dunaliella tertiolecta and its physico-chemical interaction with cadmium and copper ions were studied by electrochemical methods (differential pulse anodic stripping voltammetry (DPASV) and a.c. polarography). The interactions with cadmium and copper were studied at the model interface (mercury electrodesolution) and in the bulk phase by measuring the complexing ability of the released organic material.The axenic cultures were grown on different growth media, without and with trace metals and chelators. Culture media were analyzed 10 days after inoculation, containing 5 × 105−1.2 × 106 cells cm−3 when untreated or after separation of cells by gentle centrifugation.It was found that the content and type of the released surface-active material and complexing ligands depend on the initial composition of the growth media. In all cases, strong interaction of excreted organic substances with copper in the bulk phase and with cadmium at the model interface were observed.A rather high value of the complexing capacity, 9.5 × 10−7 mol Cu2+ dm−3, was found in the culture grown on medium without trace metals and chelators (medium I) whereas the surface activity of this culture was not high (0.2 mg dm−3 equivalent to Triton-X-100). Higher contents of surface-active material (0.8 and 1.0 mg dm−3) were found in cultures grown in media with trace metals and without chelators (II and III), accompanied by a high content of complexing ligands (5.8 × 10−7 and 9.5 × 10−7 mol Cu2+ dm−3). However, if the complexing capacity is calculated per cell the values obtained for cultures grown in media II and III (0.79 × 10−15 and 0.98 × 10−15 mol Cu2+ dm−3) are lower than for cultures grown on medium I (1.8 × 10−15 mol Cu2− dm−3). The exceptional adsorption effects and the copper complexing capacity for medium 1, and the presence of cells with degenerative symptoms can be ascribed to stressed growth conditions, and, particularly, to deficiency of metals. A qualitatively similar behaviour has been observed in natural samples of estuarine waters, indicating the existence of stressed conditions during the mixing of fresh and saline waters.  相似文献   

3.
A simple hydraulic model is used to estimate the deep water fluxes of Cretan Deep Water (CDW), through the Cretan Arc Straits and into the Eastern Mediterranean Basins. The input to the model consists of the height of the deep water reservoir above sill depth and its density difference from the overlying water masses. Data from four hydrographic cruises, which took place in 1995, 1991 and 1987, are used to estimate the depth of the reservoir above the sill and the density difference. The results show a significant CDW outflow of 0.75×106 m3 s−1 in early 1995. The outflow of CDW through Kassos Strait, in the east, is 0.53×106 m3 s−1, while 0.22×106 m3 s−1 outflows through the Antikithira Strait in the west. The model results agree with fluxes estimated from current meter observations.The CDW outflow has been neither steady nor uniform during the period 1987–95. In the Kassos Strait, the outflow commenced in 1987 and increased rapidly until 1991; since then, it appears to have stabilised. In the Antikithira Strait, in contrast, the outflow has increased steadily since 1987. Such modifications in the CDW outflow are associated with changes in its hydrographic characteristics. The salinity of CDW increased constantly, by approximately 0.1, between 1987 and 1995 while its temperature warmed, between 1987 and 1991, and then cooled.  相似文献   

4.
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   

5.
Budgets for conservative tracers are used to determine the flow through the Irish Sea and combined with available data on nutrient distributions and inputs to estimate non-conservative nutrient fluxes. Steady state salinity and caesium-137 balances yield consistent estimates of the flow through the Irish Sea of Φ≈6×104 m3s−1. Using both tracers together with a mass balance allows the inclusion of separate diffusive flux terms and results in a diffusivity estimate ofK≈450 m2s−1and a reduced flow of Φ≈4×104 m3s−1. These values are, however, sensitive to the gradients of salinity and caesium-137 concentration, which are not well defined by the observations.Following the LOICZ procedures, salinity and mass balances were combined with analogous statements for dissolved inorganic phosphorus (DIP) and dissolved inorganic nitrogen (DIN), in order to assess the non-conservative process rates. With regard to phosphorus it was found that the Irish Sea is close to balance with a slight net uptake of dissolved inorganic phosphorus, but the implied excess of uptake over release is not significant on account of uncertainties in the observations of boundary values and inputs. The DIN budget is subject to comparable uncertainties in the input data but does, however, indicate a significant imbalance with an average rate of denitrification of the order 0·3 mol N m−2y−1.The implications of these budget results and their limitations are considered in relation to the application of the budgeting approach to areas with sparse data coverage. While the application of box model disciplines to conservative tracers can lead to satisfactory estimates of advective transport, the extension to non-conservative components requires extensive data to adequately specify the boundary values and input parameters averaged over the seasonal cycle.  相似文献   

6.
A theoretical evaluation of basic thermodynamic relationships reveals that variation of activity coefficients, ion pairing and electrical interactions must be considered when modelling ionic diffusion in seawater. The contributions of ion-pair formation and change in activity coefficient along the diffusion path were studied experimentally by conducting diffusion experiments in which solutions of KCl, NaCl, MgCl2, Li2SO4, K2SO4, Na2SO4 and MgSO4, at an ionic strength of 0.7, were allowed to diffuse into distilled water. The study reveals that the thermodynamic factor, required to correct for changes in the activity coefficient along the diffusion path, is significant for all the salts studied. Agreement between a simple diffusion model, which does not include ion pairing, and observed data was good for completely dissociated salts, but poor for salts which are known to form ion pairs at the concentration levels studied. The diffusion of MgSO4, 0.425 of which is associated at I = 0.7, was successfully modelled by assuming that the diffusion coefficient of the MgSO40 ion pair is different from the diffusion coefficient of the dissociated salt. The diffusion coefficient of this ion pair is estimated to be 1.9 × 10−5 cm2 s−1 at 30°C, as compared to 0.49 × 10−5 cm2 s−1 for the dissociated salt. It is suggested that the high mobility of this ion pair could cause magnesium enrichment in pore water of sulfate depleted sediments.  相似文献   

7.
In order to investigate total organic carbon (TOC) exchange through the Strait of Gibraltar, samples were taken along two sections from the western (Gulf of Cádiz) and eastern (Western Alboran Sea) entrances of the Strait and at the middle of the Strait in April 1998. TOC was measured by using a high-temperature catalytic oxidation method. The results referenced here are based on a three-layer model of water mass exchange through the Strait, which includes the Atlantic inflow, Mediterranean outflow and an interface layer in between. All layers were characterised by a decrease of TOC concentrations from the Gulf of Cádiz to the Western Alboran Sea: from 60–79 to 59–66 μM C in the Atlantic inflow and from 40–60 to 38–52 μM C in the Mediterranean waters, respectively. TOC concentrations in the modified North Atlantic Central Water varied from 43 to 55 μM C. Intermediate TOC values were measured in the interface layer (43–60 μM C). TOC concentrations increased from the middle of the Strait towards continents indicating a contribution of organic carbon of photosynthetic origin along Spain and Morocco coasts or TOC accumulation due to upwelling in the northeastern part of the Strait. Our results indicate that the short-term variability caused by the tide greatly impacts the TOC distribution, particularly in the Gulf of Cádiz. The TOC input from the Atlantic Ocean to the Mediterranean Sea through the Strait of Gibraltar varies from 0.9×104 to 1.0×104 mol C s−1 (or 0.28×1012 to 0.35×1012 mol C year−1, respectively). This estimate suggests that the TOC inflow and outflow through the Strait of Gibraltar are two and three orders of magnitude higher than reported via the Turkish Straits and Mediterranean River inputs.  相似文献   

8.
The Great Belt, the Øresund and the Little Belt connect the central Baltic Sea and the Kattegat. A fixed station was moored in the contraction area in the Little Belt during the period 18–28 July 1995, measuring temperature, salinity and current in two levels, while discharge was measured by the RVDana. The composite Froude number calculated at the fixed station shows that the two layer flow through this area was most often supercritical. The discharges were satisfactorily related to the currents measured at the fixed station, and time-series of transports through the Little Belt were established. When compared to the transports through the Øresund the water transport ratio (Øresund:Little Belt) was found to be 4·4, while the salt transport ratio was found to be 3·0. The resistance of the Little Belt, when considering the differences in sea level from Gedser to Hornbæk, was 1839×10−12 s2 m−5. On the basis of water level and surface salinity measurements made during the period 1931–76, a net discharge of 2300 m3 s−1and a net salt transport of 36 tonnes s−1through the Little Belt from the central Baltic Sea were found.  相似文献   

9.
To characterize more fully the nature of the fluorophores present in the dissolved organic matter found in seawater, steady state and time-resolved measurements of the luminescence quenching of a number of samples of marine dissolved organic matter with known quenchers, such as iodide, acrylamide and methyl viologen (MV) (1,1′-dimethyl-4,4′-bipyridinium), were compared. Quenching characteristics of these systems were analyzed using Stern-Volmer plots for both intensity and lifetime measurements. The bimolecular quenching constants, κq, for these quenchers were found to decrease in the order MV2+ (κq 1010M−1s−1) > I− (κq 2 × 109 M−1 s−1) >CH2CHCONH2 (κq 2 × 108 M−1 s−1) for the samples measured. The results also show that different samples are quenched to differing extents by the quenchers studied, that ionic strength alters the quenching constants, and that both static and diffusional quenching mechanisms may operate.Such studies are appropriate to the quantification of the reactivity of the singlet states of the chromophores found within marine dissolved organic matter. Although excess energy of the singlet state may be readily transferred to another chemical species, the combination of competing physical deactivation paths and the low concentrations of efficient quenches in the oceans serves to lessen the direct chemical impact of this process.  相似文献   

10.
Photo-oxidation of dimethylsulphide in aqueous solution   总被引：2，自引：0，他引：2  
Dimethylsulphide (DMS) is readily photo-oxygenated in the presence of micromolar amounts of photosensitizers such as methylene blue, rose bengal, anthroquinone and humic acid. Two moles of DMS are oxidized for every mole of molecular oxygen utilized consistent with dimethyl-sulphoxide being the oxidation product. Coastal seawater samples examined contained sufficient naturally occurring photosensitizer to photo-oxygenate DMS in sunlight with a first order rate constant of 2.4 × 10−5 s−1. This rate is rapid enough to imply that DMS is oxidized at approximately the same rate as it is lost to the atmosphere.  相似文献   

11.
Dissolved Al carried in river water apparently undergoes a fractional removal at the early stages of mixing in the Conway estuary. On the other hand, dissolved Al behaves almost conservatively in high salinity (>13) estuarine waters. In order to understand the geochemistry of Al in these estuarine waters, simple empirical sorption models have been used. Partitioning of Al occurs between solid and solution phases with a distribution coefficient, Kd, which varies from 0.67 × 105 to 3.38 × 106 ml g−1 for suspended particle concentrations of 2–64 mg l−1. The Kd values in general decrease with increasing suspended particulate matter and this tendency termed the “particle concentration effect” is quite pronounced in these waters. The sorption model derived by previous workers for predicting concentrations of dissolved Al with changing suspended sediment loads has been applied to these data. Reasonable fits are obtained for Kd values of 105, 106 and 107 ml g−1 with various values of α. Further, a sorption model is proposed for particulate Al concentrations in these waters that fits the data extremely well defined by a zone with Kd value 107 ml g−1 and C0 values 16 × 10−6 mg ml−1 and 92 × 10−6 mg ml−1. These observations provide strong evidence of sorption processes as key mechanisms influencing the distribution of dissolved and particulate Al in the Conway estuary and present new insight into Al geochemistry in estuaries.  相似文献   

12.
Analyses of the concentration product (Ca2+) × (CO32−) in the pore waters of marine sediments have been used to estimate the apparent solubility products of sedimentary calcite (K′SPc) and aragonite (K′SPa) in seawater. Regression of the data gives the relation In K′PSPc = 1.94 × 10−3 δP − 14.59 The 2°C, 1 atm value of K′SPc is, then, 4.61 × 10−7 mol2 l−2. The pressure coefficient yields a at 2°C of −43.8 cm3 atm−1. A single station where aragonite is present in the sediments gives a value of K′SPa = 9.2 × 10−7 (4°C, 81 atm). The calcite data are very similar to those determined experimentally by Ingle et al. (1973) for K′SPc at 2°C and 1 atm. The calculated is also indistinguishable from the experimental results of Ingle (1975) if is assumed to be independent of pressure.  相似文献   

13.
Using manganese-impregnated fiber extraction and high-efficiency gamma counting techniques, we measured the distribution of 228Ra and 226Ra in surface waters near the coast of Japan and in the western North Pacific. There is no evidence in our data that any significant amount of 228Ra is added to open ocean surface waters from the coastal waters around Tokyo Bay. High 228Ra concentrations (> 10 dpm/103 kg), were observed along the Kuroshio Current as compared to < 2.5 dpm/103 kg between 10° and 30°N of the central gyre, and hence the major source of 228Ra in the surface water is likely to be the East Asian continental shelf zones. A simple one-dimensional eddy diffusion and advection model is used to explain the observed decrease of 228Ra from coast to the open ocean. The model results indicate two mixing regimes across the Kuroshio Current System with apparent eddy diffusion coefficients of Ky = 4 × 105 cm2 s−1 at distance y < 200 km from the coast, and Ky = 4 × 107 cm2 s−1 at y > 200 km. Along 40°N where an eastward flow of the ‘Kuroshio Extension’ prevails, an advective flow of > 0.1 knot is consistent with the observation of nearly constant 228Ra along the track.The geographical distribution pattern of 228Ra is clearly different from that of atmospherically derived 210Pb. Thus the 228Ra in surface water serves as a useful tracer that accompanies fluvially and coastally derived elements during their subsequent lateral transport toward the central gyre.  相似文献   

14.
A batch sorption technique for the determination of particle–water interactions of hydrophobic organic micropollutants under simulated estuarine conditions is described. Results are presented for the behaviour of 2,2′,5,5′-tetrachlorobiphenyl (2,2′,5,5′-TCB) in river and sea waters, both in the presence and absence of estuarine suspended particles. Adsorption onto particles in sea water was enhanced compared with adsorption in river water owing to salting out of the compound, and possibly of the particulate organic matter, in the presence of high concentrations of dissolved ions. The particle–water distribution coefficient, KD, decreased from about 120×103 to 10×103 ml g−1, and from about 150×103 to 20×103 ml g−1, in river water and sea water, respectively, over a particle concentration range of 10–1000 mg l−1. Incomplete recovery of compound from the reactor walls is partly responsible for a particle concentration effect, while artefacts relating to inadequate sediment and water phase separation were ruled out following further experiments. The particle concentration effect, which is replicated in many field studies of hydrophobic organic micropollutants, including 2,2′,5,5′-TCB, is incorporated into a simple partitioning model and is discussed in the context of the likely estuarine behaviour of such compounds.  相似文献   

15.
A liquid-liquid partition, ligand exchange procedure involving the formation of copper(II) complexes with acetylacetone is presented for the determination of stability constants and concentrations of copper chelators in seawater. Acetylacetone competes with natural ligands for copper, and the equilibrium concentration of the copper acetylacetonate complex is used in speciation calculations. The concentration of the complex is calculated by partitioning a fraction of it into an organic phase and determining the total Cu concentration in that phase by back extracting with acid, and analyzing by flameless atomic absorption spectroscopy. The concentration of Cu acetylacetonate in seawater in equilibrium with the organic phase is calculated from the partition coefficient. The simple, thermodynamically well characterized procedure offers several advantages over previous techniques. Studies using organic free seawater and model ligands show good agreement between experimental and calculated conditional stability constants. Studies from seawater in Biscayne Bay, Florida, indicate two ligand types are present; type 1, K1 = 1.2 × 1012, CL1 = 5.1 × 10−9 M; type 2, K2 = 2.8 × 1010, CL2 = 1.1 × 10−7 M. Speciation is dominated by ligand type 1. Depth profiles of [Cu(II)]free/[Cu(II)]total measured with the procedure at ambient copper concentrations show an increase from < 5 × 10−5 at 50–60 m to > 1 × 10−3 at the surface at two stations off the Florida coast.  相似文献   

16.
Copper complexing capacity of cell exudates of Dunaliella salina in natural seawater culture medium was investigated in order to evaluate the influence of this organism on speciation of trace metals in seawater.Seawater samples were collected at 200 m and 2 miles off the coast and immediately filtered. Copper complexing capacity (CCCu) and stability constants (K′) of related cupric complexes were then measured. They were, respectively, 27.1 × 10−8 mol l−1 and 0.56 × 107 l mol−1 for the samples collected at 200 m and 12.8 × 10−8 mol l−1 and 6.10 × 107 l mol−1 for those collected 2 miles off the coast. A stock culture (20 ml, 106 cells ml−1) in log-phase was inoculated in 2 l of each sample of filtered natural seawater. The trend of cell influence was estimated on filtered culture medium by measuring CCCu and K′ after 1 h, 3 and 7 days. From the results it appears that CCCu increased with respect to time and this was related to the growth rate, indicating a certain relationship with cell metabolic activity.It can be concluded that a comparison between the culture referring to 200 m and 2 miles, respectively, shows that the former presents a CCCu two times higher than the latter while the K′ is ten times higher at 2 miles than that at 200 m.  相似文献   

17.
Hourly fluctuations of vertical velocity in relation to components of flow and wind and temperature oscillations at a morring site in the shelf waters off the west coast of India are discussed. The vertical velocities were computed from a time series of vertical temperature profiles assuming that horizontal advection of temperature is negligible. The computed values at a depth of 40 m during the 72-h period of observation were of the order of 10−1 to 10−2cm s−1, with a mean value of −2·77 × 10−2 cm s−1 indicating a net upward movement of water. The computed vertical velocity showed fluctuations of about 2–3 h, in addition to weaker signals of about 12 h. Based on the spectral estimates, we speculate that these fluctuations of 2–3 h in the vertical velocity may be caused by the fluctuations in the along-shore wind. The oscillations of isotherms found in the temperaturedepth time series and the spectral estimates of temperature and cross-shore flow component showed a periodicity of about 12 h, which indicated the presence of semi-diurnal internal waves. The fact that these internal wave troughs were associated with the measured onshore flow suggested that the waves were propagating offshore. The computed stability parameters showed little evidence of instability or mixing. It was found that the isotherm troughs in the temperaturedepth time series at about 12-h period coincided with high vertical shear in the cross-shore direction and low values of Brunt Vaisälä frequency.  相似文献   

18.
Suspended particulate matter (SPM) concentration and properties (particle size and settling velocity), water column and boundary layer dynamics were measured during a 60-d period at a site in 110 m water depth in the northern North Sea. The site was in stratified waters and measurements were made during September–November as the seasonal thermocline was progressively weakening. SPM concentration was low, c. 1 mg dm−3 in the surface mixed layer and maximum values of 2 mg dm−3 in the bottom mixed layer. The bottom layer was characterised by larger mean particle size. SPM signals in the two layers were decoupled at the start of the period, when the thermocline was strong, but were increasingly coupled as the thermocline progressively weakened. A spring-neap cycle of resuspension and deposition of SPM was observed in the bottom mixed layer. Bed shear stresses were too small to entrain the bottom sediment (a fine sand) but were competent to resuspend benthic fluff: threshold bed shear stress and threshold current velocity at 10 mab were 0.02–0.03 Pa. and 0.18 m s−1, respectively. Maximum SPM concentration in the bottom layer preceded peak spring tide currents by 3 d. Simulation of fluff resupension by the PROWQM model confirms that this was due to a finite supply of benthic fluff: the fluff layer was stripped from the seabed so that fluff supply was zero by the time of peak spring flow. SPM was redeposited over neap tides. Fluff resuspension must have been enhanced by intermittent inertial currents in the bottom layer but unequivocal evidence for this was not seen. There was some resuspension due to wave activity. Settling velocity spectra were unimodal or bimodal with modal values of 2×10−4–2×10−3 mm s−1 (long-term suspension component) and 0.2–5.7 mm s−1 (resuspension component). The slowest settling particles remained in suspension at peak spring tides after the fluff layer had been exhausted. There was evidence of particle disaggregation during springs and aggregation during neaps.  相似文献   

19.
An array of five buoys and three coastal stations is used to characterize the winds, stress, and curl of the wind stress over the shelf off Bodega Bay, California. The wind and wind stress are strong and persistent in the summer and weak in the winter. In the summer, wind and stress decrease strongly across the shelf, toward the coast. Combinations of buoys are used to compute the curl of the wind stress over different portions of the shelf. The mean summer 2001 curl of the wind stress over the array depends upon the area selected, varying between −1.32×10−6 and +7.80×10−6 Pa m−1. The winter 2002 wind-stress curl also depends on location, varying from −2.06×10−6 to +2.78×10−6 Pa m−1. Mean monthly curl of the wind stress is a maximum in the summer and a minimum near zero in the winter. In both the summer and the winter, the correlation between the wind-stress curl for different portions of the shelf varies between moderate negative, though insignificance, to high positive. A wind measurement at a single point can be poorly related to the measured curl of the wind stress at other locations over the shelf. The measurements show that the use of one wind measurement to characterize the curl of the wind stress over the shelf without further investigation of the local wind-stress curl structure is risky.  相似文献   

20.
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