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1.
Solid sediment, pore and epibenthic waters were collected from the Thau lagoon (France) in order to study the post-depositional partition and mobility of mercury in organic rich sediment. Total Hg (HgT) and monomethylmercury (MMHg) profiles were produced in both dissolved and solid phases. The distribution of HgT in the solid phase appeared to be related to the historical changes in the Hg inputs into the lagoon. HgT was in equilibrium between solid and solution phases in the sulfidic part of the cores, with a mean log Kd of 4.9 ± 0.2. The solid phase appeared to be a source of HgT for pore water in the upper oxic to suboxic parts of the cores. The MMHg represented a small fraction of HgT: 3–15% and 0.02–0.80% in the dissolved and solid phases, respectively. Its distribution was characterized by a main peak in the superficial sediments, and another deeper in the core within the sulfide-accumulating zone. In addition, high dissolved MMHg concentrations and methylated percentage were found in the epibenthic water. Ascorbate (pH 8) dissolution of the sediments and analyses of the soluble fraction suggest that the amorphous oxyhydroxides played a major role in controlling total and methylmercury mobility throughout the sediment–water interface. These features are discussed in terms of sources, transfer and transformations. Diffusive fluxes of HgT and MMHg from sediment to the water column for the warm period were estimated to be 40 ± 15 and 4 ± 2 pmol m−2 d−1, respectively.  相似文献   

2.
Spatial and temporal trends in pore water geochemistry and sediment microbial community structure are compared at three intertidal sites of a saltmarsh on Sapelo Island, GA. The sites include a heavily bioturbated, unvegetated creek bank, a levee with dense growth of Spartina alterniflora, and a more sparsely vegetated ponded marsh site. The redox chemistry of the pore waters ranges from sulfide-dominated at the ponded marsh site to suboxic at the creek bank site. At the three sites, the vertical redox stratification of the pore waters is more compressed in summer than in winter. The trends in redox chemistry reflect opposing effects of sediment respiration and pore water irrigation. Intense and deep burrowing activity by fiddler crabs at the creek bank site results in the efficient oxidation of reduced byproducts of microbial metabolism and, hence, the persistence of suboxic conditions to depths of 50 cm below the sediment surface. Increased supply of labile organic substrates at the vegetated sites promotes microbial degradation processes, leading to sharper redox gradients. At the levee site, this is partly offset by the higher density and deeper penetration of roots and macrofaunal burrows. Surprisingly, the microbial community structure shows little correlation with the variable vertical redox zonation of the pore waters across the saltmarsh. At the three sites, the highest population densities of aerobic microorganisms, iron- plus manganese-reducing bacteria, and sulfate reducers coexist within the upper 10 cm of sediment. The absence of a clear vertical separation of these microorganisms is ascribed to the high supply of labile organic matter and intense mixing of the topmost sediment via bioturbation.  相似文献   

3.
A novel shipboard gas tension device (GTD) that measures total dissolved air pressure in ocean surface waters is described and demonstrated. In addition, an improved method to estimate dissolved N2 levels from simultaneous measurements of gas tension, dissolved O2, water temperature, and salinity is described. Other than a flow-through plenum, the shipboard GTD is similar to the previously described moored-mode GTD (McNeil et al., 1995, Deep-Sea Research I 42, 819–826). The plenum has an integrated water-side screen to protect the membrane, and prevent the membrane from flexing in super-saturated near surface waters. The sampling scheme uses a well mixed and thermally insulated 15 L container that is flushed by the ship's seawater intake at a rate of 3–15 L min−1. Dissolved gas sensors are placed inside this container and flushed with a small recirculation pump. Laboratory data that characterize the response of the modified GTD are presented. The modified GTD has a constant, isothermal, characteristic (e-folding) response time of typically 11±2 min at 20 °C. The response time decreases with increasing temperature and varies by ±35% over a temperature range of 5–35 °C. Results of field measurements, collected on the R.V. Brown between New York and Puerto Rico during September 2002, are presented, and provide the first look at co-variability in surface ocean N2, O2, and CO2 levels over horizontal length scales of several kilometers. Dissolved N2 concentrations decreased by approximately 16% as the ship sailed from the colder northern continental shelf waters, across the Gulf Stream, and into the warmer northwestern Atlantic Ocean. Historical database measurements, buoy time series, and satellite imagery, are used to aid interpretation of the dissolved gas levels.  相似文献   

4.
Vertical distributions of dissolved species across the sediment–water interface (SWI), including major cations (sodium, potassium, magnesium, calcium), minor cations (lithium, strontium, barium), redox sensitive species (dissolved manganese, iron, sulfate, sulfide, ammonium) and other chemical parameters (pH, alkalinity, soluble reactive phosphorous, dissolved silica) were studied in a Mediterranean lagoon used for intensive shellfish farming. In order to quantify the impact of this activity on diagenetic processes and the influence of seasonal changes, two stations contrasted with respect to organic carbon fluxes were sampled in Thau lagoon from March 2001 to August 2002 during four field campaigns in winter, spring, summer and fall. Well-defined layers enriched with redox sensitive species were observed following the conventional sequence of early diagenetic reactions. However, differences were observed between both stations in depths and thickness layers. Concentration gradients extended down to more than 92 cm depth at the central position of the lagoon (station C4 – 8 m depth) and down to 40 cm depth inside shellfish farming zones (station C5 – 9 m depth). Station C4 showed an unusual diagenetic signature: sharp dissolved oxygen, iron, nitrate and manganese gradients existed at the SWI but gradients of dissolved sulfide and alkalinity as well as other parameters (dissolved silica, Ba, etc.) were recorded only from 25 to 30 cm depth downward. Seasonal changes were observed in pore water composition as deep as 30–50 cm in station C4 (only 15 cm in station C5). The center of the lagoon is not directly subjected to biodeposits deriving from shellfish activity. Isotopic and bioturbation data allowed to rule out a reworking of the sediment deeper than a few centimeters. In addition to organic content of the sediment, physical parameters were likely to induce the 10–20 cm gap between dissolved iron and sulfide profile as well as the higher vertical extent of diagenetic sequence observed at station C4. Conversely to station C5, station C4 underwent stronger currents and wave effect probably generating advective transport of water through the sediment, but no permeability data were available to confirm this hypothesis. During summer, climatic conditions generated vertical stratification of the water column and transient suboxic conditions at the bottom. Such conditions drove the upward shift of redox fronts, compacting the diagenetic sequence. These effects were reinforced at station C5 by shellfish and its farm structures (mainly attenuation of current and increased heat absorption).  相似文献   

5.
Concentrations of dissolved sulfate and sulfur isotopic ratios of dissolved sulfide in surface sediments of the Peru shelf and upper slope indicate that the sediments can be divided into two depth intervals based on the dominant biogeochemical reactions. Although rates of bacterial sulfate reduction are high throughout Peru surface sediments, chemistry of the upper interval (<10–20 cm) is dominated by chemoautotrophic oxidation of dissolved sulfide and elemental sulfur, while the lower interval (>10–20 cm) is dominated by dissimilatory sulfate reduction. In three of the four cores examined here, pore water concentrations of sulfate in the top 10 cm of the sediment are significantly higher than those of the overlying seawater. Peak sulfate concentrations in pore water (37–53 mmol/l) are ∼1.3–1.9 times that of seawater sulfate and are located 1–6 cm below the sediment/water interface (SWI). The excess sulfate is most likely produced by oxidation of elemental sulfur coupled to reduction of nitrate, a reaction mediated by a facultative chemoautotrophic sulfide-oxidizing bacterium, Thioploca spp. Numerical simulations demonstrate that the anomalously high concentrations of dissolved sulfate can be produced by steady-state or non-steady-state processes involving high rates of bacterial oxidation of elemental sulfur. If bacterial sulfur oxidation is a transient phenomenon, then it is probably triggered by seasonal or El Niño-induced changes in water-column chemistry of the Peru undercurrent.  相似文献   

6.
The chemical speciation of iron was determined in the Southern Ocean along a transect from 48 to 70°S at 20°E. Dissolved iron concentrations were low at 0.1–0.6 nM, with average concentrations of 0.25±0.13 nM. Organic iron complexing ligands were found to occur in excess of the dissolved iron concentration at 0.72±0.23 nM (equivalent to an excess of 0.5 nM), with a complex stability of log KFeL′=22.1±0.5 (on the basis of Fe3+ and L′). Ligand concentrations were higher in the upper water column (top 200 m) suggesting in situ production by microorganisms, and less at the surface consistent with photochemical breakdown. Our data are consistent with the presence of stable organic iron-complexing ligands in deep global ocean waters at a background level of ∼0.7 nM. It has been suggested that this might help stabilise iron at levels of ∼0.7 nM in deep ocean waters. However, much lower iron concentrations in the waters of the Southern Ocean suggest that these ligands do not prevent the removal of iron (by scavenging or biological uptake) to well below the concentration of these ligands. Scavenging reactions are probably inhibited by such ligand competition, so it is likely that biological uptake is the chief cause for the further removal of iron to these low levels in waters that suffer from very low iron inputs.  相似文献   

7.
Significant quantities of fluids and dissolved geochemical components are expelled through the sediment surface in ocean margin and sedimented ridge environments. Recently, significant interest has been generated in constraining hydrological processes in these environments, but direct measurement of fluid flow in the marine environment has proven to be difficult and many aspects of marine hydrogeology remain poorly understood. To address the need for a means to make a significant number of direct measurements in a wide range of low to moderate flow environments, we have developed a new type of benthic aqueous flux meter that is capable of measuring diffuse fluid flow through the sediment surface on the order of 0.1 mm yr−1–15 m yr−1 when the flow is through sediments with permeabilities of less than 10−8 cm2 (typical seafloor sediments). The instrument measures fluid flow by determining the degree of dilution of a chemical tracer that is injected by an osmotic pump at a known rate into the fluids venting into or out of a collection chamber situated on the sea bed. The pump also withdraws a subsample of this tracer/fluid mix into sample coils allowing a serial record of the flow rates to be determined. Both upward and downward flow can be measured and, when flux rates are high enough to effectively flush the collecting chamber, the instruments also act as geochemical samplers. Three years of laboratory testing and field use have constrained the effects of (1) temperature, pressure, and deployment duration on osmotic pump performance, (2) dispersion/diffusion in the sample coils, and (3) deflection of flow under a range of sediment permeabilities. Recent deployments on the Kodiak and Cascadia accretionary prisms document the range and capabilities of the instrument in the field.  相似文献   

8.
The natural isotope 234Th is used in a small-scale survey of particle transport and exchange processes at the sediment–water interface in the Benguela upwelling area. Results from water and suspended particulate matter (SPM) samples from the uppermost and lowermost water column as well as the underlying sediment of three stations are compared. The stations are situated in different sedimentological environments at 1200–1350 m water depth at the continental slope off Namibia. Highly differing extent and particle content of the bottom nepheloid layer (BNL) are determined from transmissometer data. Three models are presented, all explaining the 234Th depletion of the BNL and 234Th excess of the surface sediment that were observed. While the first model is based solely on local resuspension of surface sediment particles, the second evaluates the influence of vertical particle settling from the surface waters on the 234Th budget in the BNL. The third model explains 234Th depletion in the BNL by sedimentation of particles that were suspended in the BNL during long-range transport. Particle inventory of the BNL is highest at a depocenter of organic matter at 25.5°S, where strong deposition is presently taking place and lateral particle transport is suggested to predominate sediment accumulation. This is supported by the high settling flux of particles out of the BNL into the sediments of the depocenter, exceeding the vertical particle flux into sediment traps at intermediate depth in the same area by up to an order of magnitude. High particle residence/removal times in the BNL above the depocenter in the range of 5–9 weeks support this interpretation. Comparison with carbon mineralization rates that are known from the area reveals that, notwithstanding the large fraction of advected particles, organic carbon flux into the surface sediment is remineralized to a large extent. The deployment of a bottom water sampler served as an in situ resuspension experiment and provided the first data of 234Th activity on in situ resuspended particles. We found a mean specific activity of 86 disintegrations per minute (dpm) g−1 (39–339 dpm g−1), intermediate between the high values for suspended particles (in situ pump: 580–760 dpm g−1; CTD rosette: 870–1560 dpm g−1) and the low values measured at the sediment surface (26–37 dpm g−1). This represents essential information for the modeling of 234Th exchange processes at the sediment–water interface.  相似文献   

9.
Ectohydrolase activities of suspended microbiota were compared to those associated with sinking particles (sed-POM) retrieved from sediment traps deployed in the permanently anoxic Cariaco Basin. In shore-based assays, activities of aminopeptidase, β-glucosidase, chitinase and alkaline phosphatase were measured in samples obtained from oxic and anoxic depths using MUF- and MCA-labeled fluorogenic substrate analogs. Hydrolysis potentials for these enzymes in the seston varied widely over the nine cruises sampled (8 Nov 1996–3 May 2000) and among depths (15–1265 m); from <10 to over 1600 nM d?1 hydrolysate released, generally co-varying with one another and with suspended particulate organic carbon (POC) and particulate nitrogen (PN). Hydrolytic potentials, prokaryotic abundances and POC/PN concentrations in sinking debris were 400–1.3×107 times higher than in comparable volumes of seawater. However when normalized to PN, hydrolytic potentials in sediment trap samples were not demonstrably higher than in Niskin bottle samples. We estimate that PN pools in sediment trap samples were turned over 2–1400 times (medians=7–26x) slower by hydrolysis than were suspended PN pools. Median prokaryotic growth rates (divisions d?1) in sinking debris were also ～150 times slower than for bacterioplankton. Hydrolytic potentials in surface oxic waters were generally faster than in underlying anoxic waters on a volumetric basis (nM hydrolysate d?1), but were not significantly (p>0.05) different when normalized to PN or prokaryote abundances. Alkaline phosphatase was consistently the most active ectohydrolase in both sample types, suggesting that Cariaco Basin assemblages were adapted to decomposing phosphate esters in organic polymers. However, phosphorus limitation was not evident from nutrient inventories in the water column. Results support the hypothesis that efficiencies of polymer hydrolysis in anoxic waters are not inherently lower than in oxic waters.  相似文献   

10.
《Marine Chemistry》2006,98(2-4):109-120
We investigated interference effects on the analysis of silver in estuarine and oceanic waters using on-line high resolution inductively coupled plasma mass spectrometry (ICP-MS). A mini-column packed with a strong anion exchange resin (Dowex 1-X8) was used in a flow-injection system to separate and concentrate silver from the saline samples prior to on-line determination by ICP-MS. A series of analyses showed the concentrations of silver measured in San Francisco Bay estuary and the North Pacific that had been acidified (pH < 2) and stored for periods of 1–2 years were 10–70% lower than those measured in aliquots of those samples after ultraviolet (UV) irradiation. Additional silver released after UV irradiation of the estuarine waters, but not the ocean waters, was positively correlated (r = 0.77, simple linear correlation) with chlorophyll-a concentrations, but not with dissolved organic carbon (DOC) concentrations. Spatial distributions of chlorophyll-a and UV-released silver also exhibited similar patterns along a salinity gradient in the San Francisco Bay estuary, suggesting an in situ biogenic source of the interferent for the silver measurements.  相似文献   

11.
The concentration of dissolved and particulate Re have been measured in the Narmada, Tapi and the Mandovi estuaries in the Arabian Sea and the Hooghly estuary in the Bay of Bengal. Re concentration in water and particulate matter of these estuaries is highly variable. Re in river waters analysed varies from 1 to 41 pmol/kg, the lowest in the Mandovi and the highest in the Mahi river. Re concentrations in the rivers analysed except in the Mandovi river are higher than the average global riverine Re concentration of 2.1 pmol/kg. Based on this study and the available data, the contemporary global annual flux of dissolved riverine Re is estimated to be ~ 350 × 103 mol with an average concentration of ~ 9.2 pmol/kg, much higher than the earlier estimates. Residence time of Re in the oceans based on this estimate is 175,000 years, ~ 4 times lower compared to earlier estimates. Re behaves conservatively in all the estuaries studied. Re concentrations of seawater in the Bay of Bengal and in the Arabian Sea, estimated from the data of the Hooghly and the Mandovi estuaries respectively are ~ 40 pmol/kg, similar to the open ocean Re values of the Arabian Sea measured in this study and the values reported for in other oceanic regions. However, the dissolved Re in the Gulf of Cambay is 2 to 5 times higher, consistent with the high Re measured in the Mahi estuary and in the coastal waters of the Gulf of Cambay. The source of high Re in the Gulf of Cambay seems to be anthropogenic, measurements of Re in rivers and industrial waste waters draining into the Gulf supply amount to ~ 2300 mol of Re annually. This anthropogenic supply coupled with high residence time of water in the Gulf contribute to its high Re. Re concentration in suspended sediments of the Narmada estuary varies from 1 to 2 pmol/g, and does not show any discernible trend with salinity.The contemporary global riverine Re supply to the oceans estimated in this study is ~ 2–4 times higher compared to its removal in the reducing (anoxic/suboxic) sediments, indicating non-steady state of Re in the ocean. High dissolved riverine Re flux coupled with high Re content in the Gulf of Cambay highlights the need of a detailed study of Re in the various global rivers and in oceans including coastal regions and semi enclosed basins of the world to understand its behaviour in various reservoirs and to constrain the residence time of Re in the ocean.  相似文献   

12.
Photochemical production rates of hydrogen peroxide (H2O2) were determined in Antarctic waters during two research cruises. The first cruise was from mid-October to mid-November, 1993, in the confluence of the Weddell and Scotia Seas, and the second cruise was in December, 1994, along the coast of the Antarctic Peninsula. During these cruises, midday sea-surface production rates ranged from 2.1 to 9.6 nM h−1, with an average rate of 4.5 nM h−1. Production rates were consistently smaller than rates determined at lower latitudes (>9 nM h−1), primarily due to the colder temperatures and lower ultraviolet irradiances in polar waters. In situ production rates were determined with a free-floating drifter that was deployed for 12–14 h. Production rates, averaged over the deployment time, were highest at or near the surface (ca. 2.4–3.5 nM h−1) and decreased rapidly with depth to 0.1–0.7 nM h−1 at 10–20 m. The decrease in production rates with depth generally paralleled the decrease in ultraviolet irradiance in the water column. Production rates of hydrogen peroxide in Antarctic seawater were largely controlled by the ultraviolet irradiance in the water column, although there was some evidence for production in the blue region of the solar spectrum. A laboratory study was conducted to determine the wavelength dependence of the apparent quantum yield for the photochemical formation of hydrogen peroxide in Antarctic waters. Apparent quantum yields determined at 0°C decreased from 0.74×10−3 mol einstein−1 at 290 nm to 1.0×10−5 mol einstein−1 410 nm. At 20°C, apparent quantum yields for the photochemical production of hydrogen peroxide were within a factor of two of apparent quantum yields determined in temperate waters at 20–25°C. Sunlight-normalized H2O2 production rates were determined as a function of wavelength using noontime irradiance data from Palmer Station, Antarctica. A decrease in stratospheric ozone from 336 to 151 Dobson units resulted in a predicted 19–42% increase in the photoproduction of H2O2 at the sea surface in Antarctic waters. The magnitude of this increase depends on the concentration and absorbance characteristics of dissolved organic matter in the photic zone, as well as on other factors such as cloudiness and decreasing solar zenith angle that tend to lower photochemical rates offsetting increases due to stratospheric ozone depletion.  相似文献   

13.
Dissolved iron and Fe(II) were measured in the oxygen minimum zone (OMZ) of the Arabian Sea in September 2004. The OMZ is a well-demarcated feature characterized by high rates of denitrification, and a deep nitrite maximum coinciding with oxygen levels below 1 μmol L−1. This zone is significantly enriched in dissolved Fe relative to overlying and underlying waters and up to 50% of the dissolved Fe is present as Fe(II). The maxima in Fe(II) are at the same depth as the deep nitrite maxima, centered around 200–250 m. They coincide with a local maximum in total dissolved Fe, suggesting that Fe accumulates at this depth because of the greater solubility of Fe(II) over Fe(III). Fe(II) is thermodynamically unstable even at submicromolar oxygen levels, so active biological reduction is the most plausible source. To our knowledge, this is the first report of a potential link between Fe reduction, elevated dissolved Fe concentrations, and nitrite accumulation within an OMZ. Denitrification has a high Fe requirement associated with the metalloenzymes for nitrate and nitrite reduction, so in situ redox cycling of Fe has important implications for the nitrogen cycle.  相似文献   

14.
We found similar microbial degradation rates of labile dissolved organic matter in oxic and suboxic waters off northern Chile. Rates of peptide hydrolysis and amino acid uptake in unconcentrated water samples were not low in the water column where oxygen concentration was depleted. Hydrolysis rates ranged from 65 to 160 nmol peptide L−1 h−1 in the top 20 m, 8–28 nmol peptide L−1 h−1 between 100 and 300 m (O2-depleted zone), and 14–19 nmol peptide L−1 h−1 between 600 and 800 m. Dissolved free amino acid uptake rates were 9–26, 3–17, and 6 nmol L−1 h−1 at similar depth intervals. Since these findings are consistent with a model of comparable potential activity of microbes in degrading labile substrates of planktonic origin, we suggest, as do other authors, that differences in decomposition rates with high and low oxygen concentrations may be a matter of substrate lability. The comparison between hydrolysis and uptake rates indicates that microbial peptide hydrolysis occurs at similar or faster rates than amino acid uptake in the water column, and that the hydrolysis of peptides is not a rate-limiting step for the complete remineralization of labile macromolecules. Low O2 waters process about 10 tons of peptide carbon per h, double the amount processed in surface-oxygenated water. In the oxygen minimum zone, we suggest that the C balance may be affected by the low lability of the dissolved organic matter when this is upwelled to the surface. An important fraction of dissolved organic matter is processed in the oxygen minimum layer, a prominent feature of the coastal ocean in the highly productive Humboldt Current System.  相似文献   

15.
The Arctic Ocean has wide shelf areas with extensive biological activity including a high primary productivity and an active microbial loop within the surface sediment. This in combination with brine production during sea ice formation result in the decay products exiting from the shelf into the deep basin typically at a depth of about 150 m and over a wide salinity range centered around S ～33. We present data from the Beringia cruise in 2005 along a section in the Canada Basin from the continental margin north of Alaska towards the north and from the International Siberian Shelf Study in 2008 (ISSS-08) to illustrate the impact of these processes. The water rich in decay products, nutrients and dissolved inorganic carbon (DIC), exits the shelf not only from the Chukchi Sea, as has been shown earlier, but also from the East Siberian Sea. The excess of DIC found in the Canada Basin in a depth range of about 50–250 m amounts to 90±40 g C m?2. If this excess is integrated over the whole Canadian Basin the excess equals 320±140×1012 g C. The high DIC concentration layer also has low pH and consequently a low degree of calcium carbonate saturation, with minimum aragonite values of 60% saturation and calcite values just below saturation. The mean age of the waters in the top 300 m was calculated using the transit time distribution method. By applying a future exponential increase of atmospheric CO2 the invasion of anthropogenic carbon into these waters will result in an under-saturated surface water with respect to aragonite by the year 2050, even without any freshening caused by melting sea ice or increased river discharge.  相似文献   

16.
Seven years (2001–2008) of dissolved organic carbon (DOC) vertical profiles were examined in order to assess the main processes determining DOC concentration and distribution in the meso- and bathypelagic layers of the Mediterranean Sea. As expected, DOC showed high and highly variable concentrations in the surface layer of 57–68 μM (average values between 0 and 100 m), with a decrease to 44–53 μM between 200 and 500 m. Deep DOC distribution was strongly affected by deep-water formation, with a significant increase to values of 76 μM in recently ventilated deep waters, and low concentrations, comparable to those observed in the open oceanic waters (34–45 μM), where the oldest, deep waters occurred. In winter 2004/2005 a deep-water formation event was observed and the consequent DOC export at depth was estimated to range between 0.76–3.02 Tg C month–1. In the intermediate layer, the main path of the Levantine Intermediate Water (LIW) was followed in order to estimate the DOC consumption rate in its core. Multiple regression between DOC, apparent oxygen utilization (AOU), and salinity indicated that 38% of the oxygen consumption was related to DOC mineralization when the effect of mixing was removed. In deep waters of the southern Adriatic Sea a DOC decrease of 6 μM, together with an AOU increase of 9 μM, was observed between the end of January 2008 and the end of June 2008 (5 months). These data indicate a rate of microbial utilization of DOC of about 1.2 μM C month−1, with 92% of the oxygen consumption due to DOC mineralization. These values are surprisingly high for the deep sea and represent a peculiarity of the Mediterranean Sea.  相似文献   

17.
We observed the origin, behavior, and flux of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), colored dissolved organic matter (CDOM), and dissolved inorganic nitrogen (DIN) in the subterranean estuary of a volcanic island, Jeju, Korea. The sampling of surface seawater and coastal groundwater was conducted in Hwasun Bay, Jeju, in three sampling campaigns (October 2010, January 2011, and June 2011). We observed conservative mixing of these components in this subterranean environment for a salinity range from 0 to 32. The fresh groundwater was characterized by relatively high DON, DIN, and CDOM, while the marine groundwater showed relatively high DOC. The DON and DIN fluxes through submarine groundwater discharge (SGD) in the groundwater of Hwasun Bay were estimated to be 1.3 × 105 and 2.9 × 105 mol d− 1, respectively. In the seawater of Hwasun Bay, the groundwater-origin DON was almost conservative while about 91% of the groundwater-origin DIN was removed perhaps due to biological production. The DON flux from the entire Jeju was estimated to be 7.9 × 108 mol yr− 1, which is comparable to some of the world's large rivers. Thus, our study highlights that DON flux through SGD is potentially important for delivery of organic nitrogen to further offshore while DIN is readily utilized by marine plankton in near-shore waters under N-limited conditions.  相似文献   

18.
The extreme birefringence of calcium carbonate (CaCO3) relative to other major components of marine particulate matter provides a basis for making optical in situ measurements of particulate inorganic carbon (PIC) in seawater. This concept was tested with a benchtop spectrophotometer equipped with a 1- and 10-cm path length sample cell and modified with linear polarizers to measure the birefringence of suspended particles. Sample suspensions containing 3–100% CaCO3 (by weight) were prepared from calcareous marine sediment material and varying amounts of non-birefringent diatomaceous earth. The samples ranged in total suspended material from 0.003 to 249 mg l−1 and PIC from 0.03 to 1820 μmol CaCO3 l−1. A positive relationship was observed between birefringence and PIC, with response falling off as the total particle concentration and the relative abundance of non-CaCO3 particles in the sample increased. Sensitivity increased linearly with optical path length, and absolute detection limits of 0.2–0.4 and 0.04–0.08 μmol CaCO3 l−1, respectively, were determined for path lengths of 1- and 10-cm based on the intrinsic signal noise of the modified spectrophotometer. Conventional (i.e., non-polarized) transmittance measurements were used to correct the birefringence signal for the sensitivity loss due to interference from scattering and absorption. Without further modification, this spectrophotometer-based method can be used (with a 10-cm cell) to quantify PIC in most surface ocean waters—including those influenced by coccolithophore blooms. The spectrophotometer results define performance requirements and design parameters for an in situ instrument capable of operating over the oceanic range of PIC.  相似文献   

19.
In the mesopelagic zone, at depths of 200–1000 m in the Monterey Submarine Canyon, CA, medusae in three genera of scyphozoa, Atolla, Periphylla and Poralia, were observed, videotaped and collected over a 9-year period (1990–1998). Environmental data were obtained simultaneously using a remotely operated vehicle (ROV) with sensors for depth, temperature, salinity and dissolved oxygen. Shipboard measurements of these same properties at two reference stations in the region defined the local water masses and helped identify species niches using the metric of spiciness and oxygen levels of the waters in which medusae were visually “captured”. The most abundant genus of mesopelagic scyphomedusae was Atolla, found associated most strongly with the spicy (warm, salty) waters of the California Undercurrent, usually above the core of the oxygen minimum zone (OMZ; O2>0.5 ml/l). The least abundant mesopelagic scyphomedusa was Periphylla, which occurred in more variable waters, including those with a greater contribution of fresher, colder (less spicy), subarctic water and, hence, most like those at the offshore California Current station in the most depleted oxygen zone (averaging O2 <0.3 ml/l). Poralia was mostly confined to the densest, coldest water, with peak abundance at the lower boundary of the OMZ (i.e., 0.3< O2<0.5 ml/l). These spiciness measures on local isopycnal surfaces within the mesopelagic zone, supported by data on dissolved oxygen concentrations, indicate highly significant but fine-scale habitat differences in species habitats in Central California waters. This in situ investigation appears to be one of only a few studies to document fine-scale, water mass affinities of mesopelagic zooplankton.  相似文献   

20.
The distribution of dissolved organic carbon (DOC) and nitrogen (DON) and particulate organic carbon (POC) and nitrogen (PON) was studied on a transect perpendicular to the Catalan coast in the NW Mediterranean in June 1995. The transect covered a hydrographically diverse zone, including coastal waters and two frontal structures (the Catalan and the Balear fronts). The cruise was conducted during the stratified period, characterized by inorganic nutrient depletion in the photic zone and a well established deep chlorophyll a maximum. DOC concentrations were measured using a high-temperature catalytic oxidation method, and DON was determined directly, with an update of the Kjeldahl method, after removal of inorganic nitrogen.The ranges of DOC and DON concentrations were 44–95 μM-C and 2.8–6.2 μM-N. The particulate organic matter ranged between 0.9 and 14.9 μM-C and from 0.1 to 1.7 μM-N. The DOC : DON molar ratio averaged 15.5±0.4, and the mean POC : PON ratio was 8.6±0.6. The distribution of dissolved organic matter (DOM) was inverse to that of the salinity. The highest concentrations of DOM were found in coastal waters and in the stations affected by the Catalan front, located at the continental shelf break.It was estimated that recalcitrant DOM constituted 67% of the DOM pool in the upper 50 m. The data suggest that accumulation of DOC due to the decoupling of production and consumption may occur in the NW Mediterranean during stratification and that the organic matter exported from the photic layer is dominated by C-rich material.  相似文献   

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