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1.
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   

2.
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   

3.
Quasi-synoptic observations of the horizontal and vertical structure of a cold-core cyclonic mesoscale eddy feature (Cyclone Noah) were conducted in the lee of Hawai’i from November 4–22, 2004 as part of the E-Flux interdisciplinary collaborative research program. Cyclone Noah appears to have spun up to the southwest of the ‘Alenuihaha Channel (between Maui and Hawai’i) as a result of strong and persistent northeasterly trade winds through the channel. Shipboard hydrographic surveys 2.5 months later suggest that Noah weakened and was in a hypothesized spin-down phase of its life cycle. Although the initial surface expression of Noah was limited in scale to 40 km in diameter and, as evidenced by surface temperatures, 2–3 °C cooler than the surrounding waters, depth profiles revealed a fully developed semi-elliptical shallow feature (200 m), 144 km long and 90 km wide (based on sigma-t=23 kg m−3) with tangential speeds of 40–80 cm s−1, and substantial isopycnal doming. Potential vorticity distribution of Noah suggests that radial horizontal flow of the core water was inhibited from the surface to depths of 75 m, with high vorticity confined above the sigma-t=23.5 kg m−3 isopycnal surface. Upward displacements of isopycnal surfaces in the eddy's center (50 m) were congruent with enhanced pigment concentrations (0.50 mg m−3). Comparisons of the results obtained for E-Flux I (Noah) and E-Flux III (Opal) suggest that translation characteristics of cyclonic Hawaiian lee eddies may be important in establishing the biogeochemical and biological responses of the oligotrophic ocean to cyclonic eddies.  相似文献   

4.
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   

5.
Benthic foraminiferal biomass, density, and species composition were determined at 10 sites in the Gulf of Mexico. During June 2001 and 2002, sediment samples were collected with a GoMex box corer. A 7.5-cm diameter subcore was taken from a box core collected at each site and sliced into 1-cm or 2-cm sections to a depth of 2 or 3 cm; the >63-μm fraction was examined shipboard for benthic foraminifera. Individual foraminifers were extracted for adenosine triphosphate (ATP) using a luciferin–luciferase assay, which indicated the total ATP content per specimen; that data was converted to organic carbon. Foraminiferal biomass and density varied substantially (2–53 mg C m−2; 3600–44,500 individuals m−2, respectively) and inconsistently with water depth: although two 1000-m deep sites were geographically separated by only 75 km, the foraminiferal biomass at one site was relatively low (9 mg C m−2) while the other site had the highest foraminiferal biomass (53 mg C m−2). Although most samples from Sigsbee Plain (>3000 m) had low biomass, one Sigsbee site had >20 mg foraminiferal C m−2. The foraminiferal community from all sites (i.e. bathyal and abyssal locales) was dominated by agglutinated, rather than calcareous or tectinous, species. Foraminiferal density never exceeded that of metazoan meiofauna at any site. Foraminiferal biomass, however, exceeded metazoan meiofaunal biomass at 5 of the 10 sites, indicating that foraminifera constitute a major component of the Gulf's deep-water meiofaunal biomass.  相似文献   

6.
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   

7.
In order to better understand the relationship between the natural radionuclide 234Th and particulate organic carbon (POC), marine particles were collected in the northwestern Mediterranean Sea (spring/summer, 2003 and 2005) by sediment traps that separated them according to their in situ settling velocities. Particles also were collected in time-series sediment traps. Particles settling at rates of >100 m d−1 carried 50% and 60% of the POC and 234Th fluxes, respectively, in both sampling years. The POC flux decreased with depth for all particle settling velocity intervals, with the greatest decrease (factor of 2.3) in the slowly settling intervals (0.68–49 m d−1) over trap depths of 524–1918 m, likely due to dissolution and decomposition of material. In contrast the flux of 234Th associated with the slowly settling particles remained constant with depth, while 234Th fluxes on the rapidly settling particles increased. Taking into account decay of 234Th on the settling particles, the patterns of 234Th flux with depth suggest that either both slow and fast settling particles scavenge additional 234Th during their descent or there is significant exchange between the particle classes. The observed changes in POC and 234Th flux produce a general decrease in POC/234Th of the settling particles with depth. There is no consistent trend in POC/234Th with settling velocity, such as might be expected from surface area and volume considerations. Good correlations are observed between 234Th and POC, lithogenic material and CaCO3 for all settling velocity intervals. Pseudo-Kds calculated for 234Th in the shallow traps (2005) are ranked as lithogenic material opal <calcium carbonate <organic carbon. Organic carbon contributes 33% to the bulk Kd, and for lithogenic material, opal and CaCO3, the fraction is 22% each. Decreases in POC/234Th with depth are accompanied by increases in the ratio of 234Th to lithogenic material and opal. No change in the relationship between 234Th and CaCO3 was evident with depth. These patterns are consistent with loss of POC through decomposition, opal through dissolution and additional scavenging of 234Th onto lithogenic material as the particles sink.  相似文献   

8.
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   

9.
This study aims at assessing the adequacy for describing bimodal sea states of different non-linear probability distributions that have been developed for single sea states. It is based on data collected at an offshore test basin. The measurements represent three bimodal sea states with individual unidirectional wave systems propagating at 60, 90 and 120 from each other. The wave spectra are separated into swell and wind sea components and the relative energy ratio between the areas under the associated spectral curves is estimated and is related with the statistics of the time series considered. Dependence is found between the normalized high order cumulants, which describe the non-Gaussian surface, and the predominant contribution of the wind sea energy. Furthermore, the probabilities of exceedance of the individual wave heights are estimated and compared with the Rayleigh model and with other models that take into account either the effect of spectral bandwidth or the effect of wave nonlinearities. The results are discussed with respect to three classes of sea states that reflect the relative contribution of swell and wind sea energy.  相似文献   

10.
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   

11.
N.K. Bigalke  G. Rehder  G. Gust   《Marine Chemistry》2009,115(3-4):226-234
The dissolution of in-situ generated methane hydrate in undersaturated, synthetic seawater (S = 35) was investigated in a series of laboratory-based experiments at P-/T-conditions within the hydrate stability field. A controlled flow field was generated across the smooth hydrate surface to test if, in addition to thermodynamic variables, the dissolution rate is influenced by changing hydrodynamic conditions. The dissolution rate was found to be strongly dependent on the friction velocity, showing that hydrate dissolution in undersaturated seawater is a diffusion-controlled process. The experimental data was used to obtain diffusional mass transfer coefficients kd, which were found to correlate linearly with the friction velocity, u. The resulting kd/u-correlation allows predicting the flux of methane from natural gas hydrate exposures at the sediment/seawater interface into the bulk water for a variety of natural P, T and flow conditions. It also is a tool for estimating the rate of hydrate regrowth at locations where natural hydrate outcrops at the seafloor persist in contact with undersaturated seawater.  相似文献   

12.
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   

13.
Delayed coincidence counters (RaDeCC), used for measuring 223Ra and 224Ra preconcentrated from water onto MnO2-impregnated acrylic fiber (“Mn-fiber”), require a standard Mn-fiber column that has a precisely known activity of 224Ra for calibration. This may be done by adding an aged 228Th standard solution to adsorb both 228Th and its daughter 224Ra quantitatively onto a Mn fiber. We used both seawater and deionized water (DIW) for testing the adsorption efficiency of Th and Ra onto Mn fibers. Our experimental results show that more than 50% of thorium (232Th and 228Th) breaks through the Mn-fiber column when DIW is used as a medium. However, near quantitative recoveries are obtained if filtered (0.45 μm) seawater is used to prepare the standard. In the case of pure DIW, the pH (initial pH  5.3) rises to > 10 after passing through the column while seawater (initial pH  7.8) changes to  7.2. Thus, the lack of thorium adsorption in DIW may be attributed to this huge increase of pH and the consequent formation of Th(OH)4 and polyhydroxyl colloids. Based on these observations, we recommend that one should use either artificial seawater or natural seawater (which has negligible 224Ra and 228Th) as a loading solution after 0.45 μm filtration. In addition, the thorium adsorption efficiency should be confirmed either by thorium analysis of the effluent solution or long-term monitoring of the supported 224Ra on the Mn fiber using the RaDeCC. Similar cautions are likely necessary for making 223Ra standards by adsorption of 227Ac onto Mn fibers.  相似文献   

14.
Biogeochemical processes in sediments under the influence of the Rhône River plume were studied using both in situ microelectrodes and ex situ sediment core incubations. Organic carbon (OC) and total nitrogen (TN) content as well as stable carbon isotopic composition of OC (δ13COC) were analysed in 19 surface sediments to determine the distribution and sources of organic matter in the Rhône delta system. Large spatial variations were observed in both the total O2 uptake (5.2 to 29.3 mmol m−2 d−1) and NH4+ release (−0.1 to −3.5 mmol m−2 d−1) rates at the sediment–water interface. The highest fluxes were measured near the Rhône River mouth where sedimentary OC and TN contents reached 1.81% and 0.23% respectively. Values of δ13COC ranged from −26.83‰ to −23.88‰ with a significant seawards enrichment tracing the dispersal of terrestrial organic matter on the continental shelf. The amount of terrestrial-derived OC reaches 85% in sediments close to the Rhône mouth decreasing down to 25% in continental shelf sediments. On the prodelta, high terrestrial OC accumulation rates support high oxygen uptake rates and thus indicating that a significant fraction of terrestrial OC is remineralized. A particulate organic carbon (POC) mass balance indicates that only 3% of the deposited POC is remineralized in prodelta sediments while 96% is recycled on the continental shelf. It was calculated that a large proportion of the Rhône POC input is either buried (52%) or remineralized (8%), mostly on the prodelta area. The remaining fraction (40%) is either mineralized in the water or exported outside the Rhône delta system in dissolved or particulate forms.  相似文献   

15.
The plankton abundance data of the Continuous Plankton Recorder (CPR) route from Bergen or Rotterdam to Weather Station Mike (6444′N, 2E) from 1949 to 1981 were analysed for long-term trends and seasonal production cycles, and were related to environmental data. The data were explored using the canonical correlation analysis and nonparametric techniques like the Nadaraya–Watson regression. While large copepods such as Calanus spp. and Metridia lucens did not show any temporal trends, a sharp decrease in the abundances of smaller copepods and phytoplankton was observed after 1960. The temporal trends were not related to the NAO, but did show a correlation with the wind direction. Seasonal abundance curves showed that production of both phytoplankton and zooplankton taxa started earlier in coastal water compared to Atlantic water. From the 1950s to the 1970s most taxa showed a delay in the start of the seasonal production cycles, indicating a reduction in the length of the productive cycle. This may to some extent explain the reduced abundance of smaller copepods, phytoplankton and other species during the 1960s and 1970s.  相似文献   

16.
Y.K. Chung  H.H. Chun   《Ocean Engineering》2008,35(7):646-652
We seek the solution of the planing of a flat plate at high Froude numbers by a perturbation procedure. The angle of attack of the plate is assumed to vary with the speed of the plate in the present study. A harmonic function K is introduced for the solution of the first-order disturbance potential which becomes the Green function in the limiting case when the Froude number tends to infinity. We get the solution of the first-order potential from Green's theorem applied to K and the first-order potential. Then we obtain the asymptotic solutions of the angle of attack α, lift L and drag D as follows:
where α1. Here W, LW, and U are the weight of the plate per unit width, wetted length, and speed of the plate, respectively.  相似文献   

17.
Modeling the vertical penetration of photosynthetically active radiation (PAR) through the ocean, and its utilization by phytoplankton, is fundamental to simulating marine primary production. The variation of attenuation and absorption of light with wavelength suggests that photosynthesis should be modeled at high spectral resolution, but this is computationally expensive. To model primary production in global 3d models, a balance between computer time and accuracy is necessary. We investigate the effects of varying the spectral resolution of the underwater light field and the photosynthetic efficiency of phytoplankton (α*), on primary production using a 1d coupled ecosystem ocean turbulence model. The model is applied at three sites in the Atlantic Ocean (CIS (60°N), PAP (50°N) and ESTOC (30°N)) to include the effect of different meteorological forcing and parameter sets. We also investigate three different methods for modeling α* – as a fixed constant, varying with both wavelength and chlorophyll concentration [Bricaud, A., Morel, A., Babin, M., Allali, K., Claustre, H., 1998. Variations of light absorption by suspended particles with chlorophyll a concentration in oceanic (case 1) waters. Analysis and implications for bio-optical models. J. Geophys. Res. 103, 31033–31044], and using a non-spectral parameterization [Anderson, T.R., 1993. A spectrally averaged model of light penetration and photosynthesis. Limnol. Oceanogr. 38, 1403–1419]. After selecting the appropriate ecosystem parameters for each of the three sites we vary the spectral resolution of light and α* from 1 to 61 wavebands and study the results in conjunction with the three different α*estimation methods. The results show modeled estimates of ocean primary productivity are highly sensitive to the degree of spectral resolution and α*. For accurate simulations of primary production and chlorophyll distribution we recommend a spectral resolution of at least six wavebands if α* is a function of wavelength and chlorophyll, and three wavebands if α* is a fixed value.  相似文献   

18.
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19.
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   

20.
Topocaustics     
Deep (2000 m) observations near the Sigsbee escarpment in the Gulf of Mexico show short-period (approximately 5–12 days) energetic currents due to topographic Rossby waves (TRW’s). We suggest that the phenomenon is due to the focusing and accumulation of TRW energy by the slopes coupled with a bend in isobaths, in a topographic caustic (topocaustic). The idea draws on a simple mathematical equivalence between the propagation of internal waves and of TRW’s. Topocaustics occur near regions of maximum NT = N|h| (N = Brunt–Väisälä frequency; h = water depth). Because of the one-sided propagation property of TRW’s, energy also tends to accumulate at the “western” end of closed contours of NT. The process is demonstrated here using a nonlinear primitive-equation numerical model with idealized bathymetry and forcing. A Gulf of Mexico simulation initialized with a data-assimilated analysis covering the period of the Sigsbee observation is then conducted. The mooring is near a localized maximum NT, and Intrinsic Mode Functions confirm the existence of energetic bursts of short-period deep-current events. The strong currents are locally forced from above, either by an extended Loop Current or a warm ring.  相似文献   

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