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1.
Concentrations of Co, Cu, Fe, Mn, Ni, Pb and Zn in four macroalgae species (Ulva lactuca, Chondracanthus squarrulosus, Sargassum sinicola and Gracilariopsis lemaneiformis) were obtained for the first time from the central part of the west coast of the Gulf of California. Generally, no differences in metal concentrations were found among the different seaweed species, although spatial differences were apparent. Iron, Mn and Cu exhibited higher concentrations at the stations located in front of Angel de la Guarda Island, probably because of high vertical mixing processes present in the zone. The results were compared with dissolved metal concentrations reported for the Gulf of California (Cd, Mn and Fe) and the North Pacific Ocean. The resulting linear regression of the results vs. North Pacific Ocean concentrations indicated that the levels of Cu, Ni and Zn measured in this study were within its 95% confidence level. Furthermore, this comparison was capable of detecting dissolved Fe and Mn enrichments in Gulf of California waters relative to the North Pacific Ocean concentrations. Calculations of total masses of metals associated with algal biomass on the west coast of the Gulf of California indicated that the lowest masses were represented by Cu (108 ± 25 kg) and Ni (184 ± 52 kg), whereas Pb (1.1 ± 0.6 ton) and Fe (10.9 ± 8.5 ton) were the elements with the highest associated masses.  相似文献   

2.
Trace metal clean techniques were used to sample Hawaii Ocean Time-series (HOT) station ALOHA on seven occasions between November 1998 and October 2002. On three occasions, full water-column profile samples were obtained; on the other four occasions, surface and near-surface euphotic zone profiles were obtained. Together with three other published samplings, this site may have been monitored for “dissolved” (≤0.4 or ≤0.2 μm) Fe more frequently than any other open ocean site in the world.Low Fe concentrations (<0.1 nmol kg−1) are seen in the lower euphotic zone, and Fe concentrations increase to a maximum in intermediate waters. In the deepwaters (>2500 m), the concentrations we observe (0.4-0.5 nmol kg−1) are significantly lower than some other deep North Pacific stations but are similar to values that have been reported for a station 350 miles to the northeast. We attribute these low deepwater values to transport of low-Fe Antarctic Bottom Water into the basin and a balance between Fe regeneration and scavenging in the deep water. Near-surface waters have higher Fe levels than observed in the lower euphotic zone. Significant temporal variability is seen in near-surface Fe concentrations (ranging from 0.2-0.7 nmol kg−1); we attribute these surface Fe fluctuations to variable dust deposition, biological uptake, and changes in the mixed layer depth. This variability could occur only if the surface layer Fe residence time is less than a few years, and based on that constraint, it appears that a higher percentage of the total Fe must be released from North Pacific aerosols compared to North Atlantic aerosols. Surprisingly, significant temporal variability and high particulate Fe concentrations are observed for intermediate waters (1000-1500 m). These features are seen in the depth interval where high δ3He from the nearby Loihi Seamount hydrothermal fields has been observed; the total Fe/3He ratio implies that the hydrothermal vents are the source of the high and variable Fe.The vertical profile of Mn at ALOHA qualitatively resembles other North Pacific Mn profiles with surface and intermediate water maxima, but there are some significant quantitative differences from other reported profiles. The ≤0.4 μm Mn concentration is highest near the surface, decreases sharply in the upper 500 m, then shows an intermediate water maximum at 800 m and then decreases in the deepest waters; these concentrations are higher than observed at a station 350 miles to the northeast that shows similar vertical variations. It appears that there is a significant Mn gradient (throughout the water column) from HOT towards the northeast.Compared to the first valid oceanic Pb data for samples collected in 1976, Pb at ALOHA in 1997-1999 shows decreases in surface waters and waters shallower than 200 m. Pb concentrations in central North Pacific surface waters have decreased by a factor of 2 during the past 25 yr (from ∼65 to ∼30 pmol kg−1); surface water Pb concentrations in the central North Atlantic and central North Pacific are now comparable. We attribute the surface water Pb decrease to the elimination of leaded gasoline in Japan and to some extent by the U.S. and Canada. We attribute most of the remaining Pb in Pacific surface waters to Asian emissions, more likely due to high-temperature industrial activities such as coal burning rather than to leaded gasoline consumption. A 3-year mixed-layer time series from the nearby HALE-ALOHA mooring site (1997-1999) shows that there is an annual cycle in Pb with concentrations ∼20% higher in winter months; this rise may be created by downward mixing of the winter mixed layer into the steep gradient of higher Pb in the upper thermocline (Pb concentrations double between the surface and 200 m). From 200 m to the bottom, Pb concentrations decrease to levels of 5-9 pmol kg−1 near the bottom; for most of the water column, thermocline and deepwater Pb concentrations do not appear to have changed significantly during the 23-yr interval.  相似文献   

3.
全球海水剖面Fe同位素组成存在显著不均一性.对大西洋洋中脊、大西洋近海岸带、东太平洋和西太平洋弧后扩张中心多个站位的海水剖面溶解Fe浓度和Fe同位素组成进行了综合分析,得出以下主要认识:（1）不同区域的海水剖面溶解Fe浓度和Fe同位素组成呈现不同的变化特征,海水Fe同位素的变化趋势与海水溶解氧浓度变化一致,而与海水溶解Fe浓度呈镜像变化关系;（2）不同深度的海水溶解Fe浓度和Fe同位素组成特征的主要控制因素不同.表层海水受到大气降尘、生物作用影响呈现富重Fe同位素特征,受河流的影响Fe同位素组成偏轻;深层海水主要受到深海沉积和海底热液活动的影响,其中沉积物中的非还原溶解Fe导致海水富集重Fe同位素,而受洋中脊热液流体影响的深部海水显著富集轻Fe同位素;（3）将目前已知海底热液溶解Fe通量最小值（0.5 Gmol/a）作为全球大洋的热液溶解Fe通量,利用不同来源的溶解Fe同位素与其通量间的关系估算海底热液对海洋的Fe循环的贡献为~5.5%.由于海底热液流体的Fe通量可能远大于0.5 Gmol/a,因此,海底热液活动对海洋溶解Fe的贡献可能远超过前人的估算结果（6.0%）.   相似文献   

4.
Particulate Fe and Mn may be important trace metal scavengers in the water column as well as being probable indicators of biologically mediated redox processes. A study has been made of suspended particulate composition in the Santa Barbara Basin, a shallow near-shore basin off southern California with sub-oxic conditions below sill depth. Observations have revealed several interesting phenomena relating to the geochemistry of Fe and Mn. Most striking is a profound enrichment of particulate Fe in samples from the bottom two hundred meters. These particulates have a constant Fe/P mole ratio of about three and may originate at the sediment-water interface or may be transported to the basin from local marshes. For particulate Mn, enrichments are observed both in the sub-sill waters and near the base of the euphotic zone. A consideration of particle removal rates suggests that the sub-photic zone enrichment has a biogenic origin. In the sub-sill waters, enrichment in Mn is apparently due to the precipitation of dissolved Mn diffusing from the anoxic basin sediments. A simple mass balance suggests that most of the Mn lost from the sediments is transported from the Santa Barbara Basin in dissolved form.  相似文献   

5.
Co-rich Mn crusts from four different locations of the world ocean have been studied to understand the role of dissolved oxygen of the ambient seawater in the formation of Co-rich Mn crusts. WOCE (World Ocean Circulation Experiment) oxygen profiles of modern seawater in the Equatorial North Pacific Ocean, Equatorial South Indian Ocean and the North East Atlantic Ocean have been evaluated with respect to the occurrence of Co-rich Mn crusts at depths ranging from 1500 to 3200 m. The oxygen content at these depths varied from ∼90–240 µmol/kg. The oxygen minimum zone (OMZ), with oxygen contents in the range ∼45–100 µmol/kg, is located in the depth range 800–900 m in these regions. The age of the ocean crust on which seamounts formed is in the range 80.3–180 Ma. Profiles of the oxygen contents of seawater with depth in the oceans are shown to be extremely useful in establishing the optimum conditions for the formation of Co-rich Mn crusts. The use of WOCE oxygen profiles to study geochemical processes in the oceans is highly recommended.  相似文献   

6.
Lake Joyce is one of the least studied lakes of the McMurdo Dry Valleys. Similar to other lakes in this region, Lake Joyce is a closed-basin, permanently ice-covered, meromictic lake. We present here a detailed investigation of major ions, nutrients, and dissolved trace elements for Lake Joyce. Specifically, we investigate the role of iron and manganese oxides and hydrous oxides in trace metal cycling.Lake Joyce is characterized by fresh, oxic waters overlying an anoxic brine, primarily Na–Cl. Surface waters have a maximum nitrate concentration of 26M with a molar dissolved inorganic nitrogen to phosphorus ratio of 477. The supply of nitrogen is attributed to atmospheric deposition, possibly from polar stratospheric clouds. Dissolved phosphorus is scavenged by hydrous iron oxides. The pH is highest (10.15) just beneath the 7-m thick ice cover and decreases to a minimum of 7.29 in the redox transition zone. Dissolved Al exceeds 8M in surface waters, and appears to be controlled by equilibrium with gibbsite. In contrast, concentrations of other trace elements in surface waters are quite low (e.g., 5.4nM Cu, 0.19nM Co, <20pM La). Dissolved Fe, Mn, Ni and Cd were below our detection limits of 13 nM, 1. 8 nM, 4.7 nM and 15pM (respectively) in surface waters. There was a 6-m vertical separation in the onset of Mn and Fe reduction, with dissolved Mn appearing higher in the water column than Fe. Based on thermodynamic calculations, dissolved Mn appears to be controlled by equilibrium with hausmannite (Mn3O4). Co tracks the Mn profile closely, suggesting Co(III) is bound in the lattice of Mn oxides, whereas the Ce profile is similar, yet the Ce anomaly suggests oxidative scavenging of Ce. Release of Cu, Ni, Cd and trivalent REE appears to be controlled by pH-induced desorption from Fe and Mn oxides, although Cu (and perhaps Ni) may be scavenged by organic matter in surface waters.  相似文献   

7.
The spatial and temporal variability of cobalt in the Atlantic Ocean was investigated by means of adsorptive cathodic stripping voltammetry. A vertical profile of total dissolved cobalt at the Bermuda Atlantic Time Series station ranged from 17 to 73 pM and displayed surface depletion indicative of biological utilization. This profile when compared with a cobalt profile from the northeast Pacific shows no increase in deep-water concentrations with thermohaline circulation through the deep ocean basins. Moreover, the middepth maximum observed in northeast Pacific profiles is not present in the Sargasso Sea, perhaps because of the lack of cobalt scavenging by particulate manganese oxides in surface waters and to the absence of a suboxic oxygen minimum zone, which, if present, could dissolve the manganese oxides.Total dissolved cobalt measurements were also made on a surface transect from the Sargasso Sea to coastal Massachusetts, USA, and on time-series samples from the Moored In Situ Trace Element Serial Sampler. Dissolved cobalt on this transect correlated strongly with salinity (r2 = 0.93) and ranged from 19 to 133 pM, indicating mixing of cobalt from shelf waters into the Sargasso Sea. Time-series samples near Bermuda did not show an obvious response to the summer maximum in aeolian dust deposition, with an annual average of 20 ± 10 pM at 40- to 47-m depths. By use of this annual value and particulate cobalt data from the literature, 100-m surface-water residence times were calculated to be as low as 0.32 yr for cobalt. Several sharp decreases in cobalt were observed in the time series that occurred simultaneously with a shallowing of the thermocline depth. These decreases could be caused by nutrient drawdown associated with higher productivity mesoscale eddy events.A west-east surface transect across the South Atlantic showed high cobalt concentrations at the boundaries of the transect and low concentrations in the center despite the high precipitation rates in the intertropical convergence zone. Phosphate measurements showed the similar trends as the total cobalt transect. A regression of cobalt vs. phosphate reveals a slope that is an order of magnitude higher than that of the northeast Pacific and that is similar to the slopes observed for zinc vs. phosphate in the Pacific.  相似文献   

8.
Data are presented describing the changes in the distribution of dissolved and particulate Mn observed over a 16-month period in the periodically anoxic waters of Saanich Inlet, a fjord located on the coast of Vancouver Island, British Columbia. During the spring and summer when the bottom waters were anoxic, a dense cloud of particulate Mn was found at mid-depths where Mn2+ enriched anoxic bottom waters were mixing with oxygenated waters; then, during the autumn aand winter following an intrusion which reoxygenated the bottom water, an intense precipitation of Mn was observed throughout the entire water column. During this latter period, dissolved Mn concentrations in the bottom water, which exceeded 1000 nmol/l under anoxic conditions, decreased towards a lower limit of 1.6 nmole/l, a value comparable to that observed in Pacific Ocean waters of similar pH and dissolved oxygen content. Mn in the particulate matter collected just above the oxic-anoxic interface was found to have an average oxidation number of +3.05; and, on this basis, it is proposed that dissolved Mn concentrations in oceanic waters are controlled by the precipitation of the metastable oxide mineral manganite (γ-MnOOH), a hypothesis consistent with the fact that dissolved Mn values in subsurface Pacific Ocean waters closely approach the equilibrium solubility of this phase. Temporal and spatial gradients in the particulate Mn distribution were used to calculate the in situ rate of Mn precipitation, and the results of these calculations then were fitted to theoretical rate equations which suggest that the precipitation of Mn is controlled by 2 parallel processes: bacterial oxidation and an inorganic autocatalytic oxidation reaction.  相似文献   

9.
Subterranean estuary occupies the transition zone between hypoxic fresh groundwater and oxic seawater, and between terrestrial and marine sediment deposits. Consequently, we hypothesize, in a subterranean estuary, biogeochemical reactions of Fe respond to submarine groundwater discharge (SGD) and sea level rise. Porewater and sediment samples were collected across a 30-m wide freshwater discharge zone of the Indian River Lagoon (Florida, USA) subterranean estuary, and at a site 250 m offshore. Porewater Fe concentrations range from 0.5 μM at the shoreline and 250 m offshore to about 286 μM at the freshwater-saltwater boundary. Sediment sulfur and porewater sulfide maxima occur in near-surface OC-rich black sediments of marine origin, and dissolved Fe maxima occur in underlying OC-poor orange sediments of terrestrial origin. Freshwater SGD flow rates decrease offshore from around 1 to 0.1 cm/day, while bioirrigation exchange deepens with distance from about 10 cm at the shoreline to about 40 cm at the freshwater-saltwater boundary. DOC concentrations increase from around 75 μM at the shoreline to as much as 700 μM at the freshwater-saltwater boundary as a result of labile marine carbon inputs from marine SGD. This labile DOC reduces Fe-oxides, which in conjunction with slow discharge of SGD at the boundary, allows dissolved Fe to accumulate. Upward advection of fresh SGD carries dissolved Fe from the Fe-oxide reduction zone to the sulfate reduction zone, where dissolved Fe precipitates as Fe-sulfides. Saturation models of Fe-sulfides indicate some fractions of these Fe-sulfides get dissolved near the sediment-water interface, where bioirrigation exchanges oxic surface water. The estimated dissolved Fe flux is approximately 0.84 μM Fe/day per meter of shoreline to lagoon surface waters. Accelerated sea level rise predictions are thus likely to increase the Fe flux to surface waters and local primary productivity, particularly along coastlines where groundwater discharges through sediments.  相似文献   

10.
Vertical distributions of particulate silica, and of production and dissolution rates of biogenic silica, were determined on two N-S transects across the Pacific sector of the Antarctic Circumpolar Current during the austral spring of 1978. Particulate silica profiles showed elevated levels in surface water and near the bottom, with low (35–110 nmol Si · 1?1) and vertically uniform values through the intervening water column. Both the particulate silica content of the upper 200 m and the production rate of biogenic silica in the photic zone increased from north to south, reaching their highest values near the edge of the receding pack ice. A significant, but variable, fraction (18–58%) of the biogenic silica produced in the surface layer was redissolving in the upper 90–98 m. Net production of biogenic silica in the surface layer (production minus dissolution) was proceeding at a mean rate of ca. 2 mmol Si · m?2 · day?1. This is ca. 4 times greater than the most recent estimate of the mean accumulation rate of siliceous sediments beneath the ACC. We estimate, based on mass balance, that the mean dissolution rate of biogenic silica in subsurface water column in the Southern Ocean is 1.2–2.9 mmol Si · m?2 · day?1.  相似文献   

11.
The concentrations of Rare Earth Elements (REE) and Redox Sensitive Elements (RSE) were measured in groundwaters along a transect of the forest-marsh interface of a surficial aquifer system in North Inlet, SC. The well transect extended from a forest recharge area across the marsh and tidal creek to a tidal recharge area of beach ridge. The concentrations of the RSE (Fe, Mn, and U) were consistent with reducing conditions through the transect. Fe was present at concentrations ranging from a few micromolar to greater than one hundred micromolar in most wells. U was depleted with respect to salinity predicted concentrations, indicating removal with respect to the seawater endmember. Dissolved Mn concentrations were generally low in all wells, indicating no significant solid source of Mn (as MnOx) in this system. When extrapolated to a global scale, estimates of U removal during seawater exchange with the aquifer solids equaled 10–20% of the total riverine dissolved U input flux. REE concentrations in the forest recharge area were high in shallow wells, and showed a light enriched fractionation pattern, characteristic of soil leaching by Natural Organic Matter (NOM) rich waters. A decrease in REE concentration with depth in the forest wells coupled with a trend towards Heavy REE (HREE) enriched fractionation pattern indicated removal of the REE coincident with NOM and Dissolved Organic Carbon (DOC) removal. The saline waters of the beach ridge wells show a Light REE (LREE) enriched fractionation pattern and have the highest overall concentrations of the REE, indicating a significant REE source to the seawater endmember waters. The concentration gradients along the beach ridge flow path indicate a large source in the deep wells, and net export of dissolved REE to the tidal creek system and the coastal ocean. Ultrafiltration experiments indicate a transition from a colloidal dominated reservoir for the REE in the forest wells to a colloidal and dissolved reservoir in the beach ridge wells. The ultrafiltration data coupled with a correlation with Dissolved Inorganic Carbon (DIC) release suggest that there is diagenetic mobilization of an REE rich organic carbon phase in the saline endmember wells. We suggest here that degradation of this relic terrestrial organic carbon and REE rich phase results in the export of dissolved REE equal to or exceeding river inputs in this region.  相似文献   

12.
《Geochimica et cosmochimica acta》1999,63(13-14):1991-1999
Vertical profiles of dissolved indium and yttrium were determined in the eastern North Atlantic and the Mediterranean Sea to compare with those of the North Pacific reported earlier. The Y concentrations in the surface waters are 120 pmol/kg in the North Atlantic and 205 pmol/kg in the Mediterranean Sea, which are significantly higher than 80 pmol/kg in the North Pacific. The difference may be attributable to the different strength of input of Y to the oceans from fluvial and aeolian sources. In contrast, the deep water concentration of Y increases in the order of North Atlantic < Mediterranean < North Pacific. This trend is similar to that of dissolved Si, suggesting that Y is involved in the biogeochemical regeneration cycle. The vertical profiles of In are far more complex than Y. The In profile shows a systematic increase from 0.6 pmol/kg at the surface to 1.7 pmol/kg at 2100 m in the North Atlantic, whereas it is almost featureless at a mean concentration of 3.8 ± 0.6 pmol/kg in the Mediterranean Sea. The North Atlantic and Mediterranean In concentrations are considerably higher than those observed in the North Pacific (∼0.1 pmol/kg), and such a large interoceanic variation has been reported before only for Al and Ga. Like Al, the deep water In concentration that decreases in the order of Mediterranean > North > North Pacific exhibits an inverse trend of Y and nutrients. Indium is highly particle-reactive (47% association in the Mediterranean Sea), and must have a short mean oceanic residence time. However, the featureless dissolved In profile in the Mediterranean Sea is clearly different from the profiles of dissolved Al, showing increase with depth Hydes et al 1988, Measures and Edmond 1988, suggesting that significant fractionation of the two elements is taking place in the ocean.The interoceanic variations of dissolved In and Al may be ascribed to the different intensities of external input of which aeolian has been considered to be major rather than fluvial. However, the difference of In and Al concentrations in the deep waters of the above oceanic basins are significantly greater than those of other refractory elements, such as Ce, Ti, Hf, and Zr, whose major sources to the ocean are also considered to be aeolian. Furthermore, the In/Al ratios in seawater are about two orders of magnitude greater than the average crustal ratio. Thus, some additional sources, though not yet certain, may be required to explain the high concentrations of In in the Atlantic and the Mediterranean deep waters.  相似文献   

13.
Volcanogenic sediments are typically rich in Fe and Mn-bearing minerals that undergo substantial alteration during early marine diagenesis, however their impact on the global biogeochemical cycling of Fe and Mn has not been widely addressed. This study compares the near surface (0-20 cm below sea floor [cmbsf]) aqueous (<0.02 μm) and aqueous + colloidal here in after ‘dissolved’ (<0.2 μm) pore water Fe and Mn distributions, and ancillary O2(aq), and solid-phase reactive Fe distributions, between two volcanogenic sediment settings: [1] a deep sea tephra-rich deposit neighbouring the volcanically active island of Montserrat and [2] mixed biosiliceous-volcanogenic sediments from abyssal depths near the volcanically inactive Crozet Islands archipelago. Shallow penetration of O2(aq) into Montserrat sediments was observed (<1 cmbsf), and inferred to partially reflect oxidation of fine grained Fe(II) minerals, whereas penetration of O2(aq) into abyssal Crozet sediments was >5 cmbsf and largely controlled by the oxidation of organic matter. Dissolved Fe and Mn distributions in Montserrat pore waters were lowest in the surface oxic-layer (0.3 μM Fe; 32 μM Mn), with maxima (20 μM Fe; 200 μM Mn) in the upper 1-15 cmbsf. Unlike Montserrat, Fe and Mn in Crozet pore waters were ubiquitously partitioned between 0.2 μm and 0.02 μm filtrations, indicating that the pore water distributions of Fe and Mn in the (traditionally termed) ‘dissolved’ size fraction are dominated by colloids, with respective mean abundances of 80% and 61%. Plausible mechanisms for the origin and composition of pore water colloids are discussed, and include prolonged exposure of Crozet surface sediments to early diagenesis compared to Montserrat, favouring nano-particulate goethite formation, and the elevated dissolved Si concentrations, which are shown to encourage fine-grained smectite formation. In addition, organic matter may stabilise authigenic Fe and Mn in the Crozet pore waters. We conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water, which may impact significantly on deep ocean biogeochemistry. Diffusive flux estimates from Montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved Mn to the bottom waters, and therefore a source for the widespread hydrogenous MnOx deposits found in the Caribbean region.  相似文献   

14.
The behaviour of arsenic in muddy sediments of the Bay of Biscay (France)   总被引：1，自引：0，他引：1  
We have studied particulate and dissolved arsenic species in sediment and porewaters at sites in the Bay of Biscay, France, ranging in depths from 150 to 2,800 m. At all stations, major redox species (oxygen, nitrate, ammonia, total and reactive iron and manganese, sulphate and sulphur) reflect early diagenetic depth sequences of redox reactions comparable to other marine environments. Vertical distributions of dissolved and particulate As species and major redox species are related to changes in redox conditions and their major carrier phases, such as Fe and Mn-oxides. Arsenic diagenesis appears strongly dependent on Fe cycling. A subsurface maximum of dissolved As and surface enrichment of particulate As correspond to dissolution and precipitation of Fe (III) phases. Except for the shallowest and most bioturbated site, flux calculations show three different vertical diffusive As fluxes: two upwards and one downwards. Phase changes of recycled As result in local accumulations of reactive As at different redox fronts. Mass-balance calculations indicate that the upward As flux toward the oxidized layer can explain the enrichment of HCl extractable particulate As in this layer. A portion of the upward diffusing As can escape the sediment and may be fixed onto settling Fe-oxides by adsorption or co-precipitation and contribute to reactive particulate As input (i.e., As is recycled across the water sediment interface).  相似文献   

15.
The depth distributions of Cd, Mn and Fe in pore water and sediment were determined on three replicate box cores collected at a 325 m deep station in the Laurentian Trough. The results reveal a surface layer in which the content of solid-phase Cd first decreases but then increases sharply with depth. In contrast, Mn decreases regularly over the same depth interval. In the oxygenated zone of this layer, Cd, probably associated with organic matter, is released to the pore water, resulting in concentrations that are more than an order of magnitude higher than in the overlying water column. Some of the dissolved Cd is returned to the water column and some migrates downward and is precipitated at depth. This part of the Cd cycle is virtually complete within the surface layer, the base of which corresponds to the base of the zone of Mn enrichment.In the subsurface layer, solid-phase Cd and Mn show little or no concentration change. However, dissolved Cd, which reaches often non-detectable concentrations (<0.05 nM) in this layer, increases once again deep within the anaerobic zone and attains concentrations even higher than in the surface layer. The presence of dissolved Cd complexes (revealed by 1.5 to 8 fold increases in electrochemically active Cd in pore water following UV-treatment) as well as inconsistent distributions of dissolved and solid-phase Cd, indicate complexities in diagenesis that merit further investigation.  相似文献   

16.
Reactions occurring on the surfaces of biogenic carbonate minerals can have important consequences for the biogeochemical cycle of carbon. In this study, carbonate mineral surface reactions with ambient seawater were investigated by atomic force microscopy (AFM). A sampling method was developed in which calcite surfaces were hung at discrete depths on a sediment trap array line for a three-day deployment period in subtropical North Pacific waters. Changes in surface morphologies were examined at nanometer resolution and evaluated using as a constraint the depth profile of calcite saturation in these waters. Evidence suggests that: (1) organic films which develop on carbonate surfaces exposed to shallow seawater may be responsible for the oversaturated state of the upper oceanic water column, (2) dissolution of carbonate minerals within the shallow warm layer of the ocean could be responsible for part of the alkalinity anomaly observed in the North Pacific.  相似文献   

17.
The distribution of arsenic (As(III), As(V)) and iron (Fe(II), Fe(III)) species was monitored during 1 year in a borehole drilled in the Carnoulès tailings impoundment which contains As-rich pyrite. The concentrations of total As and Fe in subsurface waters exhibited strong variations over one year, which were controlled by dissolved oxygen concentrations. At high oxygen levels, extremely high As (up to 162 mM) and Fe (up to 364 mM) concentrations were reached in the borehole, with the oxidised species predominant. As and Fe concentrations decreased 10-fold under oxygen-deficient conditions, as a result of pH increase and subsequent precipitation of As(V) and Fe(III). From drill core sections, it appeared that at low dissolved oxygen levels, As(III) was primarily released into water by the oxidation of As-rich pyrite in the unsaturated zone. Subsequent As and Fe precipitation was promoted during transport to the saturated zone; this reaction resulted in As enrichments in the sediment below the water table compared to the original content in pyrite, together with the formation of As-rich (up to 35 wt% As) ferruginous material in the unsaturated zone. High amounts of As(V) were released from these secondary phases during leaching experiments with oxygenated acid sulfate-rich waters; this process is believed to contribute to As(V) enrichment in the subsurface waters of the Carnoulès tailings during periods of high dissolved oxygen level.  相似文献   

18.
《Applied Geochemistry》2005,20(7):1391-1408
Surface water samples from the St. Lawrence River were collected in order to study the processes controlling minor and trace elements concentrations (Al, Fe, Mn, Cd, Co, Cu, Ni and Zn), and to construct mass balances allowing estimates of the relative importance of their natural and anthropogenic sources. The two major water inputs, the upper St. Lawrence River, which drains waters originating from the Lake Ontario, and the Ottawa River were collected fortnightly over 18 months. In addition, other tributaries were sampled during the spring floods. The output was monitored near Quebec City at the river mouth weekly between 1995 and 1999. Dissolved metal concentrations in the upper St. Lawrence River carbonated waters were lower than in the acidic waters of the tributaries draining the crystalline rocks of the Canadian shield and the forest cover. Biogeochemical and hydrodynamic processes occurring in Lake Ontario drive the seasonal variations observed in the upper St. Lawrence River. Biogeochemical processes relate to biological uptake, regeneration of organic matter (for Cd and Zn) and oxyhydroxide formation (for Mn and Fe), while hydrodynamic processes mainly concern the seasonal change in vertical stratification (for Cd, Mn, and Zn). In the Ottawa River, the main tributary, oxyhydroxide formation in summer governs seasonal patterns of Al, Fe, Mn, Cd, Co and Zn. The downstream section of the St. Lawrence River is a transit zone in which seasonal variations are mainly driven by the mixing of the different water masses and the large input of suspended particulate matter from erosion. The budget of all dissolved elements, except Fe and Zn, was balanced, as the budget of particulate elements (except Cd and Zn). The main sources of metals to the St. Lawrence River are erosion and inputs from tributaries and Lake Ontario. Direct anthropogenic discharges into the river accounted for less than 5% of the load, except for Cd (10%) and Zn (21%). The fluxes in transfer of dissolved Cd, Co, Cu and Zn species from the river to the lower St. Lawrence estuary were equal to corresponding fluxes calculated for Quebec City since the distributions of dissolved concentrations of these metals versus salinity were conservative. For Fe, the curvature of the dilution line obtained suggests that dissolved species were removed during early mixing.  相似文献   

19.
Fractionation by ultra-filtration of the dissolved organic material (DOM) in the River Beaulieu, with typical concentrations of dissolved organic carbon (DOC) of 7–8 mg C/l, showed it to be mainly in the nominal molecular weight range of 103–105, with 16–23% of the total DOC in the fraction > 105. The molecular weight distribution of DOM in the more alkaline River Test (average DOC, 2 mg C/l) was similar. In the River Beaulieu water, containing 136–314 βg Fe/l in ‘dissolved’ forms, 90% or more of this Fe was in the nominal molecular weight fraction > 105. Experiments showed that DOM of nominal molecular weight <105 could stabilize Fe(III) in ‘dissolved’ forms. The concentrations of ‘dissolved’ Fe in the river water probably reflect the presence of colloidal Fe stabilized by organic material and this process may influence the apparent molecular weight of the DOM. Dissolved. Mn (100–136 βg/l) in the River Beaulieu was mainly in true solution, probably as Mn(II), with some 30% in forms of molecular weight greater than ca 104.During mi xing in the Beaulieu Estuary, DOC and dissolved Mn behave essentially conservatively. This contrasts with the removal of a large fraction of the dissolved Fe (Holliday and LISS, 1976, Est. Coastal Mar. Sci. 4, 349–353). Concentrations of lattice-held Fe and Mn in suspended particulate material were essentially uniform in the estuary, at 3.2 and 0.012%, respectively, whereas the non-lattice held fractions decreased markedly with increase in salinity. For Mn the decrease was linear and could be most simply accounted for by the physical mixing of riverborne and marine participates, although the possibility that some desorption occurs is not excluded. The non-linear decrease in the concentration of non-lattice held Fe in particulates reflected the more complex situation in which physical mixing is accompanied by removal of material from the ‘dissolved’ fraction.  相似文献   

20.
The distributions of particulate elements (Al, P, Mn, Fe, Co, Cu, Zn, Cd, and Pb), dissolved trace metals (Mn, Fe, Co, Cu, Zn, and Cd), and dissolved nutrients (nitrate, phosphate, and silicic acid) were investigated in the Gulf of the Farallones, a region of high productivity that is driven by the dynamic mixing of the San Francisco Bay plume, upwelled waters, and California coastal surface waters. Particulate metals were separated into >10 and 0.4-10 μm size-fractions and further fractionated into leachable (operationally defined with a 25% acetic acid leach) and refractory particulate concentrations. Dissolved metals (< 0.4 μm pore-size filtrate) were separated into colloidal (0.03-0.4 μm) and soluble (<0.03 μm) fractions. The percent leachable particulate fractions ranged from 2% to 99% of the total particulate concentration for these metals with Mn and Cd being predominantly leachable and Fe and Al being predominantly refractory. The leachable particulate Pb concentration was associated primarily with suspended sediments from San Francisco Bay and was a tracer of the plume in coastal waters. The particulate trace metal data suggest that the leachable fraction was an available source of trace metal micronutrients to the primary productivity in coastal waters. The dissolved trace metals in the San Francisco Bay plume and freshly upwelled surface waters were similar in concentration, with the exception of Cu and Co, which exhibited relatively high concentrations in plume waters and served as tracers of this water mass. The dissolved data and estimates of the plume dynamics suggest that the impact of anthropogenic inputs of nutrients and trace metals in the San Francisco Bay plume contributes substantially to the concentrations found in the Gulf of the Farallones (10-50% of estimated upwelled flux values), but does not greatly disrupt the natural stoichiometric balance of trace metal and nutrient elements within coastal waters given the similarity in concentrations to sources in upwelled water. In all, the data from this study demonstrate that the flux of dissolved nutrients and bioactive trace metals from the San Francisco Bay plume contribute to the high and relatively constant phytoplankton biomass observed in the Gulf of the Farallones.  相似文献   

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