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1.
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   

2.
Highly sensitive STOX O2 sensors were used for determination of in situ O2 distribution in the eastern tropical north and south Pacific oxygen minimum zones (ETN/SP OMZs), as well as for laboratory determination of O2 uptake rates of water masses at various depths within these OMZs. Oxygen was generally below the detection limit (few nmol L−1) in the core of both OMZs, suggesting the presence of vast volumes of functionally anoxic waters in the eastern Pacific Ocean. Oxygen was often not detectable in the deep secondary chlorophyll maximum found at some locations, but other secondary maxima contained up to ~0.4 µmol L−1. Directly measured respiration rates were high in surface and subsurface oxic layers of the coastal waters, reaching values up to 85 nmol L−1 O2 h−1. Substantially lower values were found at the depths of the upper oxycline, where values varied from 2 to 33 nmol L−1 O2 h−1. Where secondary chlorophyll maxima were found the rates were higher than in the oxic water just above. Incubation times longer than 20 h, in the all-glass containers, resulted in highly increased respiration rates. Addition of amino acids to the water from the upper oxycline did not lead to a significant initial rise in respiration rate within the first 20 h, indicating that the measurement of respiration rates in oligotrophic Ocean water may not be severely affected by low levels of organic contamination during sampling. Our measurements indicate that aerobic metabolism proceeds efficiently at extremely low oxygen concentrations with apparent half-saturation concentrations (Km values) ranging from about 10 to about 200 nmol L−1.  相似文献   

3.
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   

4.
Between 2 and 3 km depth, North Pacific deep waters contain a plume of water with high silicic acid concentrations. The plume extends outward from Cascadia Basin (the Washington Margin), where waters can contain in excess of 200 μM off the coast of Oregon and Washington. To identify the source of the high Si concentrations in Cascadia Basin, we measured silicic acid and germanium concentrations in deep waters, and their fluxes from sediments using incubated cores. The mean flux of silicic acid into bottom waters is 0.81±0.05 mmol/m2-day, and the Ge/Si ratio of this flux is 0.7±0.1 μmol/mol. A box model, incorporating these results with hydrographic data, indicates that (1) no more than 5% of the silicic acid added to Basin deep waters can have a hydrothermal source (either hot or warm seeps), and (2) the total input of silicic acid to Basin deep waters is 0.06±0.02 Tmol/y. This input is nearly all from remineralized biogenic debris and should contribute about 0.5% of the 14 Tmol/y that are estimated to be necessary to maintain the North Pacific plume.  相似文献   

5.
The aqueous speciation of rhenium at the temperatures on or near the Earth's surface, especially in anoxic environments, is not well known. For the first time, the relative importance of ReO4− and the neutral rhenium species, Re(OH)40, is thermodynamically modeled in anoxic environments at ambient temperature where ReS2 or its solid solution(s) is likely to control the solubility. This thermodynamic model suggests that ReO4− is an insignificant species in anoxic environments. In comparison to observed total rhenium concentrations in anoxic waters (from ∼3 to ∼30 pmol/kg), the contribution from ReO4− would be less than 10−8 ppb (∼4×10−5 pmol/kg). In contrast, the neutral rhenium species is an important species in anoxic environments. At ΣH2S=10−4 molal, 10−2 ppb (∼40 pmol/kg) of Re(OH)40 can exist in equilibrium with ReS2 in the HS− field at a pH of about 9 or under the oxygen fugacity conditions imposed by the HS−/SO42− redox couple, demonstrating its importance in anoxic environments. Applications of the present study to the Black Sea indicate that rhenium concentrations in the anoxic water column at depths ranging from 105 to ∼390 m can be successfully modeled as Re(OH)40, implying that the dominant species in solution may be Re(OH)40.  相似文献   

6.
Data collected from hydrographic stations occupied within the Venezuelan and Columbian basins of the Caribbean Sea from 1922 through 2003 are analyzed to study the decadal variability of deep temperature in the region. The analysis focuses on waters below the 1815-m sill depth of the Anegada–Jungfern Passage. Relatively dense waters (compared to those in the deep Caribbean) from the North Atlantic spill over this sill to ventilate the deep Caribbean Sea. Deep warming at a rate of over 0.01 °C decade–1 below this sill depth appears to have commenced in the 1970s after a period of relatively constant deep Caribbean Sea temperatures extending at least as far back as the 1920s. Conductivity–temperature–depth station data from World Ocean Circulation Experiment Section A22 along 66°W taken in 1997 and again in 2003 provide an especially precise, albeit geographically limited, estimate of this warming over that 6-year period. They also suggest a small (0.001 PSS-78, about the size of expected measurement biases) deep freshening. The warming is about 10 times larger than the size of geothermal heating in the region, and is of the same magnitude as the average global upper-ocean heat uptake over a recent 50-year period. Together with the freshening, the warming contributes about 0.012 m decade–1 of sea level rise in portions of the Caribbean Sea with bottom depths around 5000 m.  相似文献   

7.
The relationship between particulate organic carbon (POC) concentrations measured in modern sediment and fluxes of exported POC to the sediment surface needs to be understood in order to use POC content as a proxy of paleo-environmental conditions. The objective of our study was to compare POC concentrations, POC mineralization rates calculated from O2 consumption and POC burial rates. Benthic O2 distributions were determined in 58 fine-grained sediment cores collected at different periods at 14 stations in the southeastern part of the Bay of Biscay with depths ranging from 140 to 2800 m. Depth-dependent volume-specific oxygen consumption rates were used to assess rates of aerobic oxidation of organic matter (OM), assuming that O2 consumption solely was related to heterotrophic activity at the sediment–water interface. Heterogeneity of benthic O2 fluxes denoted changes in time and space of fresh organic material sedimentation. The most labile fraction of exported POC engendered a steep decrease in concentration in the upper 5 mm of vertical O2 profiles. The rupture in the gradient of O2 microprofile may be related to the bioturbation-induced mixing depth of fast-decaying carbon. Average diffusive O2 fluxes showed that this fast-decaying OM flux was much higher than buried POC, although diffusive O2 fluxes underestimated the total sediment oxygen demand, and thus the fast-decaying OM flux to the sediment surface. Sedimentary POC burial was calculated from sediment mass accumulation rate and the organic carbon content measured at the top of the sediment. The proportion of buried POC relative to total exported POC ranged at the most between 50% and 10%, depending on station location. Therefore, for a narrow geographic area like the Bay of Biscay, burial efficiency of POC was variable. A fraction of buried POC consisted of slow-decaying OM that was mineralized within the upper decimetres of sediment through oxic and anoxic processes. This fraction was deduced from the decrease with depth in POC concentration. At sites located below 500 m water depth, where the fast-decaying carbon did not reach the anoxic sediment, the slow-decaying pool may control the O2 penetration depth. Only refractory organic material was fossilized in sedimentary records at locations where labile OM did not reach the anoxic portion of the sediment.  相似文献   

8.
Iodide oxidation to iodate in near-surface waters of the open oceans is an elusive process, and an unequivocal demonstration of it would simplify modelling of the marine iodine system. In the open ocean, the upward advection of iodate complicates any mathematical treatment of the problem. In this context, the high concentration (0.1 μM) of iodate in the Black Sea surface waters suggested that this Sea might be a place where oxidation might be demonstrated. Hydrologically, the surface waters of the Black Sea appear to be downstream of the deeper waters and, given the latter's anoxicity, the surface waters seemed likely to gain most of their iodine as iodide by upward advection. To test this further, prior to experimentation, an iodine budget for the near-surface waters, based upon the latest hydrological model of the Sea was prepared; this predicts a minimum oxidation flux of 3.89×10−4 mol I m−2 a−1. The chemistry of this oxidation is discussed in the light of existing knowledge of the sulfide system. It is argued that as the redox potential of the IO3−/I− and I2/I− couples at pHs typical of the Black Sea (7.75) are much higher than that of the sulfate–sulfide couple, iodide is probably oxidized in the near-surface domain. This contrasts with sulfide oxidation in the suboxic zone. The possible role of nitrifying bacteria in the oxidation is discussed.  相似文献   

9.
The distribution of dissolved iron and its chemical speciation (organic complexation and redox speciation) were studied in the northeastern Atlantic Ocean along 23°W between 37 and 42°N at depths between 0 and 2000 m, and in the upper-water column (upper 200 m) at two stations further east at 45°N10°W and 40°N17°W in the early spring of 1998. The iron speciation data are here combined with phytoplankton data to suggest cyanobacteria as a possible source for the iron binding ligands. The organic Fe-binding ligand concentrations were greater than that of dissolved iron by a factor of 1.5–5, thus maintaining iron in solution at levels well above it solubility. The water column distribution of the organic ligand indicates in-situ production of organic ligands by the plankton (consisting mainly of the cyanobacteria Synechococcus sp.) in the euphotic layer and a remineralisation from sinking biogenic particles in deeper waters. Fe(II) concentrations varied from below the detection limit (<0.1 nM) up to 0.55 nM but represented only a minor fraction of 0% to occasionally 35% of the dissolved iron throughout the water column. The water column distribution of the Fe(II) suggests biologically mediated production in the deep waters and photochemical production in the euphotic layer. Although there was no evidence of iron limitation in these waters, the aeolian iron input probably contributed to a shift in the phytoplankton assemblage towards increased Synechococcus growth.  相似文献   

10.
Benthic fluxes of O2, titration alkalinity (TA), total inorganic carbon (TIC), Ca2+, NO3−, NH4+, PO43−, and Si(OH)4 were measured by in situ benthic flux chamber incubations at 13 locations on the North Carolina continental slope. The majority of measurements were made at water depths of approximately 700–850 m, in the previously identified upper slope depocenter. This region is characterized by extremely high organic matter deposition rates and near saturation bottom water oxygen concentrations. Measured benthic fluxes of TA are reasonably correlated with O2 benthic fluxes. Because bottom waters are supersaturated with respect to calcite and aragonite at these shallow water depths, these results demonstrate the importance of metabolically driven dissolution in this region. Subtraction of the calcium carbonate dissolution contributions from the TIC benthic fluxes suggests rates of organic matter remineralization ranging from 0.97 to 3.9 mol C m−2 yr−1 at the depocenter sites, a factor of 3–10 greater than estimated for the adjacent continental rise and upper slope areas. Because biological primary production in the overlying waters does not follow this pattern, these extremely high values are most likely supported by lateral inputs of highly reactive organic matter. Mass balance calculations indicate that despite the oxygenated bottom water conditions, 68% of the organic nitrogen released during organic matter remineralization processes is ultimately denitrified. The release of PO43− from the depocenter sediments is equivalent to or larger than that predicted from the remineralization of Redfield organic matter. This implies either that PO43− is preferentially released in this setting and that the accumulating sediments must be depleted in PO43− relative to organic carbon or that another, non-organic, phase is contributing PO43− to the system. The molar ratio of the Si benthic flux and organic carbon remineralization rate ranges from 0.30 to 0.86. This is significantly greater than the ratio reported for most pelagic diatoms. Possible reasons for this high ratio include the deposition of benthic diatoms that may have a larger Si : C ratio than pelagic diatoms, the near-bottom lateral input of partially reworked organic matter that may have an elevated Si : C ratio relative to fresh diatoms, preferential loss of carbon in sinking particulates or the release of Si from non-opaline materials.  相似文献   

11.
Five vertical profiles of silver (Ag) in the subarctic northeast Pacific are presented. Dissolved (< 0.2 μm) Ag concentrations within the surface mixed layer range from 6–25 pM, with the highest observed values at the most coastal site. Elevated Ag concentrations at this station are most likely attributable to the estuarine circulation in the Juan de Fuca Strait. One open-ocean station (P20) exhibited a strong surface Ag maximum. The station was located at the edge of a Haida eddy which raises the possibility that such eddies transport Ag seaward from the coastal zone. Ag concentrations in the deep waters ranged from 60–80 pM. These measurements are consistent with other recent Ag data collected in the Pacific. Ag profiles throughout the Pacific Ocean yield a strong positive correlation between Ag concentration and dissolved silicic acid concentration. However, Ag is depleted relative to silicic acid at intermediate depths where dissolved O2 concentrations are low, implying a possible removal of Ag from oxygen-depleted waters by scavenging and/or precipitation.  相似文献   

12.
Elevated methane (CH4) concentrations (128–2692×103 nM) occur in the hypersaline anoxic brine pools of Bannock and Urania Basins, eastern Mediterranean Sea, compared to low concentrations (17–80×103 nM) in the sediments below the anoxic brines. The CH4 enrichment in the brines might be due to the long residence time of the brine in the Basin. An attempt is made to determine the sources for the enriched dissolved CH4 by considering the influence of hydrothermal activity, the occurrence of sapropel layers (biogenic) and dissolution of gas hydrates. Furthermore, it is suggested that the enriched CH4 in Bannock and Urania Basins is diffused and mixed with the overlying waters by local upward transport mechanisms that selectively move CH4 upward in these Basins.  相似文献   

13.
Variations in the nutrient concentrations were studied during two cruises to the Arabian Sea. The situation towards the end of the southwest monsoon season (September/October 1994) was compared with the inter-monsoonal season during November and December 1994. Underway surface transects showed the influence of an upwelling system during the first cruise with deep, colder, nutrient-rich water being advected into the surface mixed layer. During the southwesterly monsoon there was an area of coastal Ekman upwelling, bringing colder water (24.2°C) into the surface waters of the coastal margin. Further offshore at about 350 km there was an area of Ekman upwelling, as a result of wind-stress curl, north of the Findlater Jet axis; this area also had cooler surface water (24.6°C). Further offshore (>1000 km) the average surface temperatures increased to >27°C. These waters were oligotrophic with no evidence of the upwelling effects observed further inshore. In the upwelling regions nutrient concentrations in the close inshore coastal zone were elevated (NO3=18 μmol l-1, PO4=1.48 μmol l-1); higher concentrations also were measured at the region of offshore upwelling off the shelf, with a maximum nitrate concentration of 12.5 μmol l-1 and a maximum phosphate concentration of 1.2 μmol l-1. Nitrate and phosphate concentrations decreased with increasing distance offshore to the oligotrophic waters beyond 1400 km, where typical nitrate concentrations were 35.0 nmol l-1 (0.035 μmol l-1) in the surface mixed layer. A CTD section from the coastal shelf, to 1650 km offshore to the oligotrophic waters, clearly showed that during the monsoon season, upwelling is one of the major influences upon the nutrient concentrations in the surface waters of the Arabian Sea off the coast of Oman. Productivity of the water column was enhanced to a distance of over 800 km offshore. During the intermonsoon period a stable surface mixed layer was established, with a well-defined thermocline and nitracline. Surface temperature was between 26.8 and 27.4°C for the entire transect from the coast to 1650 km offshore. Nitrate concentrations were typically between 2.0 and 0.4 μmol l-1 for the transect, to about 1200 km where the waters became oligotrophic, and nitrate concentrations were then typically 8–12 nmol l-1. Ammonia concentrations for the oligotrophic waters were typically 130 nmol l-1, and are reported for the first time in the Indian Ocean. The nitrogen/phosphorus (N/P) ratios suggest that phytoplankton production was potentially nitrogen-limited in all the surface waters of the Arabian Sea, with the greatest nitrogen limitation during the intermonsoon period.  相似文献   

14.
Iodate (IO3−) is the predominant dissolved species of iodine in the oxygenated waters of the Mediterranean Sea. Iodide (I−) is present in significant quantities (up to 65 nM) in oxygenated waters in the photic zone and near the interface above the anoxic and saline Bannock Basin. Lesser quantities of I− (< 10 nM) are found throughout the rest of the oxic water column. An additional unidentified dissolved iodine species is present immediately above the anoxic interface.Total dissolved iodine (ΣI) increases dramatically across the seawater/brine interface. Part of this increase is undoubtedly the result of the dissolution of iodine-rich evaporites during formation of the brine bodies at the Tyro and Bannock Basins. The vertical distribution of ΣI and other dissolved chemical species (particularly PO43−) in the Bannock Basin brine, however, suggests an additional, present-day, diagenetic source of dissolved iodine to the brine. Based on the increase in the concentration of the most soluble major ions across the seawater/brine interface, 5–7 μM of the 11.5-μM increase in ΣI concentration must be attributed to diagenesis.  相似文献   

15.
Sulfate reduction rate measurements by the 35SO42− core injection method were carried out in situ with a benthic lander, LUISE, and in parallel by shipboard incubations in sediments of the Black Sea. Eight stations were studied along a transect from the Romanian shelf to the deep western anoxic basin. The highest rates measured on an areal basis for the upper 0–15 cm were 1.97 mmol m−2 d−1 on the shelf and 1.54 mmol m−2 d−1 at 181 m water depth just below the chemocline. At all stations sulfate reduction rates decreased to values <3 nmol cm−3 d−1 below 15 cm depth in the sediment. The importance of sulfate reduction relative to the total mineralization of organic matter was very low, 6%, on the inner shelf, which was paved with mussels, and increased to 47% on the outer shelf at 100 m depth. Where the oxic–anoxic interface of the water column impinged on the sea floor at around 150 m depth, the contribution of sulfate reduction increased from >50% just above the chemocline to 100% just below. In the deep sea, mean sulfate reduction rates were 0.6 mmol m−2 d−1 corresponding to an organic carbon oxidation of 1.3 mmol m−2 d−1. This is close to the mean sedimentation rate of organic carbon over the year in the western basin. A comparison with published data on sulfate reduction in Black Sea sediments showed that the present results tend to be higher in shelf sediments and lower in the deep-sea than most other data. Based on the present water column H2S inventory and the H2S flux out of the sediment, the calculated turnover time of H2S below the chemocline is 2100 years.  相似文献   

16.
We report dissolved iron (Fed) concentrations measured in the upper 600 m in the central region of the Gulf of California (GC) under spring conditions. Our results showed the complex nature of Fe cycling within the GC. In the northern region of the study area, surface waters were relatively enriched, with Fed concentrations >5.0 nM, which can be partially explained by an atmospheric source. These concentrations are 12 times higher than those found in the adjacent Pacific Ocean. In contrast, Fed depth profiles in the southern region did not show any Fed surface enrichment (concentrations <1.5 nM) because of particle scavenging and higher stratification of the water-column. The most southern station in our area of study was the most stratified and showed an excess Fed and PO4 with respect to NO3, conditions favorable for nitrogen fixation. This station also showed the least negative surface value of N* of all stations. However, despite the adequate levels of Fed and PO4 at that location, the surface temperature (22.6 °C) was probably not high enough for diazotrophs to develop. A slight increase in Fed levels in intermediate waters at the southern region was associated with the oxygen minimum zone. Finally, our results suggest that remineralization of organic matter is probably the major source of Fed in subsurface waters of the GC.  相似文献   

17.
Iron could play a key role in controlling phytoplankton biomass and productivity in high-nutrient, low-chlorophyll regions. As a part of the iron fertilization experiment carried out in the western subarctic Pacific from July to August 2004 (Subarctic Pacific iron Experiment for Ecosystem Dynamics Study II—SEEDS II), we analysed the concentrations of trace gases in the seawater for 12 d following iron fertilization. The mean concentrations of chlorophyll a in the mixed layer (5–30 m depth) increased from 0.94 to 2.81 μg L–1 for 8 d in the iron patch. The mean concentrations of methyl bromide (CH3Br; 5–30 m depth) increased from 6.4 to 13.4 pmol L–1 for 11 d; the in-patch concentration increased relative to the out-patch concentration. A linear correlation was observed between the concentrations of 19′-hexanoyloxyfucoxanthin, which is a biomarker of several prymnesiophytes, and CH3Br in the seawater. After fertilization, the air–sea flux of CH3Br inside the patch changed from influx to efflux from the ocean. There was no clear evidence for the increase in saturation anomaly of methyl chloride (CH3Cl) due to iron fertilization. Furthermore, CH3Cl fluxes did not show a tendency to increase after fertilization of the patch. In contrast to CH3Br, no change was observed in the concentrations of bromoform (in-patch day 11 and out-patch day 11: 1.7 and 1.7 pmol L–1), dibromomethane (2.1 and 2.2 pmol L–1), and dibromochloromethane (1.0 and 1.2 pmol L–1, respectively). The concentration of isoprene, which is known to have a relationship with chlorophyll a, did not change in this study. The responses of trace gases during SEEDS II differed from the previous findings (in situ iron enrichment experiment—EisenEx, Southern Ocean iron experiment—SOFeX, and Subarctic Ecosystem Response to Iron Enrichment Study—SERIES). Thus, in order to estimate the concomitant effect of iron fertilization on the climate, it is important to assess the induction of biological activity and the distributions/air–sea fluxes of trace gases by iron addition.  相似文献   

18.
This study was performed in order to obtain information on the influence of an acute anoxic event (September, 1997) on distribution and speciation of inorganic iodine in the water column of a small, intensely eutrophicated salt lake. The variations in iodate and iodide depth distributions during the investigated period (1998–2000) were in accord with seasonal changes in redox conditions. During the stratification period (spring and summer), the concentration ratio between iodate and iodide in the upper layers was high, whereas during late summer and autumn, as a result of water column de-stratification and mixing of highly reducing deep water with the oxic layer, lower ratios and more uniform depth distributions were observed.The massive mortality of lake organisms induced by anoxic conditions and sulphide presence throughout the water column was registered by the end of September 1997, when overturn of the lake occurred. The concentrations of iodate in the oxic upper layers were elevated for more than a year after the mass-mortality event (up to 0.55 μmol L−1), whereas iodide concentrations remained high for more than 2 years in deep anoxic water (up to 2.27 μmol L−1). These data suggest that biogeochemical renewal processes affecting the concentrations of inorganic iodine in the lake water are slow compared to those that govern the speciation of iodine. The role of sediment–water interactions and iodine-rich organic species in the production of iodide are discussed.  相似文献   

19.
Seafloor mapping of the central Lomonosov Ridge using a multibeam echo-sounder during the Beringia/Healy–Oden Trans-Arctic Expedition (HOTRAX) 2005 shows that a channel across the ridge has a substantially shallower sill depth than the ∼2500 m indicated in present bathymetric maps. The multibeam survey along the ridge crest shows a maximum sill depth of about 1870 m. A previously hypothesized exchange of deep water from the Amundsen Basin to the Makarov Basin in this area is not confirmed. On the contrary, evidence of a deep-water flow from the Makarov to the Amundsen Basin was observed, indicating the existence of a new pathway for Canadian Basin Deep Water toward the Atlantic Ocean. Sediment data show extensive current activity along the ridge crest and along the rim of a local Intra Basin within the ridge structure.  相似文献   

20.
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   

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