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1.
Chemical extraction techniques show that the majority of the arsenic in North Atlantic deep-sea sediments is associated with an iron phase compositionally similar to that found in deep-sea ferromanganese nodules (As/Fe ～ 11 · 10?4) and is probably of seawater origin. Some sediments also contain As associated with Fe oxides produced by continental weathering. A minority (～8%) of the arsenic is of detrital origin but is not associated with Fe or Mn oxides; it has a content (1.7 ppm) similar to the average crustal abundance. In the Eastern Mediterranean Sea, near-shore sediments contain As associated with land-derived Fe oxides (As/Fe ～ 2 · 10?4), but As/Fe ratios increase to ～ 13 · 10?4 in deep-sea sediments as the contribution of seawater derived arsenic becomes dominant. Arsenic is enriched in metalliferous sediments (As/Fe ～ 20?50 · 10?4) but As/P ratios of metalliferous sediments, deep-sea ferromanganese nodules and deep-ocean water are all similar. Although a hydrothermal contribution cannot be discounted, it is likely that the arsenic is also of seawater origin, suggesting that hydrothermal iron oxyhydroxides remove As more efficiently from seawater than do iron phases (goethite) in deep-sea sediments and nodules. Arsenic accumulates in deep-sea sediments (～ 6 μg cm?2 10?3 yr?1) at sediments (～ 120 μg cm?2 10?3 yr?1) at rate sufficient to balance river input input (～3 · 1010 g yr?1). These estimates give an oceanic residence time for arsenic of 1–2 · 105 yr.  相似文献   

2.
GEOCHEMICAL CHARACTERISTICS OF INTERSTITIAL WATER OF THE BOHAI GULF   总被引：1，自引：0，他引：1  
This paper discusses the geochemical characteristics of the interstitial water of the Bohai Gulf, where the main salt contents (K+, Na+, Ca++ Mg+ + , C1-, HCO3-, SO4-) in 55 sedimentary layers of 13 cores (3-4 m in length) and those of bottom seawater have been determined and the exchange capacity and exchange cations (K+, Na+, Ca++, Mg++) of the layers analysed (see Fig. 1)Fig. J. The stations of core samplings in the Bohai Gult.  相似文献   

3.
The concentrations of dissolved chromium in seawater of the Bohai Gulf vary from trace to 1.6 μg /1 while those of particulate chromium from trace to 8.66 μg/1, indicating that the concentration of chromium in seawater of nearshore and estuary in the Bohai Gulf is higher than that of offshore, and reflecting the effects of estuarine and terrestrial pollutions. Observation data indicate that there is a positive correlation between particulate chromium and COD.The result shows that organic matter in seawater has a strong ability to combine chromium. When particulate chromium meets with seawater in estuary, it gradually settles down to sea-bottom sediments. Ratio of particulate chromium to total chromium in the Bohai Gulf yields a higher value, exceeding 90% in estuarine area, i.e. particulate chromium is a predominant form in seawater of the Bohai Gulf.  相似文献   

4.
Uranium in coastal sediments of Tokyo Bay and Funka Bay   总被引：2，自引：0，他引：2  
The sediment cores from Tokyo Bay and Funka Bay were analyzed for U and its isotopic ratio,234U/238U, after dissolving them in 0.1 M HCl, and 30% H2O2 in 0.05 M HCl. A small fraction of U in the anoxic sediments was dissolved in 0.1M HCl and even the added yield tracer,232U, was lost. The isotopic ratio of H2O2 soluble U in the sediments was equal to that of seawater, suggesting that the H2O2 soluble U in the sediments is authigenic. The 6M HCl solution dissolved part of the lithogenic U besides the authigenic U. The depth profiles of U from the two bays resembled each other. The authigenic U comprised more than half of the total U even at the surface and increased with depth down to 70 cm, showing small maxima at about 20 cm. The concentration of refractory U was nearly constant with depth and similar to that of the pelagic sediments. The highest U concentration, 6 µg g–1 which was about 5 times that of the pelagic sediments, was observed in the layer between 70 and 160 cm depth in Tokyo Bay. The annual sedimentation rates of U in the Tokyo Bay sediments were 2.6 tons at the surface and 7.0 tons at the 70–160 cm depth. The increase in U with depth should be due to the deposition of interstitial U either diffusing downward from the surface indicating the trapping of seawater U, or otherwise diffusing upward from the deeper layer indicating the internal cycling of U within the sediments.  相似文献   

5.
Sediment cores and grab samples were collected in the Upper Gulf of Thailand to determine sedimentation rates and to determine if metal concentrations reflect anthropogenic inputs.Accumulation rates of sediments in the Upper Gulf measured using the 210Pb method, appear to vary from ca. 4 to 11 mm yr?1. Sediment budgets suggest that little of the sediment delivered to the Upper Gulf by the major rivers is ultimately transported to the Lower Gulf. Metal concentrations in Upper Gulf sediments appear to be dominantly controlled by natural inputs.  相似文献   

6.
The distribution of rare-earth elements and gold have been measured in surface sediments of cores collected along a traverse across the East Pacific Rise at approximately 39° S latitude. The shale-normalized rare earth pattern of crestal sediments supports a seawater source. In samples from the flanks of the rise, concentrations of individual rare earths increase with an increase in Al2O3, suggesting that the contribution by lithogenic material becomes significant, in addition to the seawater contribution.The concentration of gold in flank sediments also suggests a lithogenic origin. In crestal sediments, however, unlike the rare earths, its concentration increases over its concentration in flank sediments. It is concluded that similar to iron, which also exhibits a maximum in crestal sediments, a fraction of the gold in these sediments has a volcanogenic source.  相似文献   

7.
We used a research submersible to obtain 33 sediment samples from chemosynthetic communities at 541–650 m water depths in the Green Canyon (GC) area of the Gulf of Mexico slope. Sediment samples from beneath an isolated mat of H2S-oxidizing bacteria at GC 234 contain oil (mean = 5650 ppm) and C1–C5 hydrocarbons (mean = 12,979 ppm) that are altered by bacterial oxidation. Control cores away from the mat contain lower concentrations of oil (mean = 2966 ppm) and C1–C5 hydrocarbons (mean = 83.6 ppm). Bacterial oxidation of hydrocarbons depletes O2 in sediments and triggers bacterial sulfate reduction to produce the H2S required by the mats. Sediment samples from GC 185 (Bush Hill) contain high concentrations of oil (mean = 24,775 ppm) and C1–C5 hydrocarbons (mean = 11,037 ppm) that are altered by bacterial oxidation. Tube worm communities requiring H2S occur at GC 185 where the sea floor has been greatly modified since the Pleistocene by accumulation of oil, thermogenic gas hydrates, and authigenic carbonate rock. Venting to the water column is suppressed by this sea-floor modification, enhancing bacterial activity in sediments. Sediments from an area with vesicomyid clams (GC 272) contain lower concentrations of oil altered by bacterial oxidation (mean = 1716 ppm) but C1–C5 concentrations are high (mean = 28,766 ppm). In contrast to other sampling areas, a sediment associated with the methanotrophic Seep Mytilid I (GC 233) is characterized by low concentration of oil (82 ppm) but biogenic methane (C1) is present (8829 ppm).  相似文献   

8.
With the rising cost of oil the electric power generating companies are turning to coal as a fuel source. Large amounts of fly ash are produced as a by product of coal combustion. This fly ash must then be disposed of, with the oceans being considered an alternative to land fill disposal. This research investigated the sorptive behavior of the surface-associated arsenic and utilized the results to project arsenic's impact on the water column during the ocean disposal of fly ash.Several acid digests were investigated to determine an effective method of arsenic recovery from fly ash. Of these, the HCl digest was the most effective technique, yielding 100% arsenic recoveries from fly-ash particles. The arsenic content of the fly ashes studied varied from 69 ± 11 μg g−1 to 323 ± 24 μg g−1, reflecting differences in the arsenic content of the source coal. In both seawater and freshwater there is an increase in arsenic desorption with increasing pH. The greatest release of arsenic occurred at pH 12 with generally over 80% of the surface arsenic released.Fly ash in contact with seawater and freshwater can exhibit either acidic or alkaline tendencies depending upon the soluble elemental composition on the surface of the flyash particle. The acidic ashes were shown to leach a greater percentage of arsenic (16.9%) than the more alkaline ashes (8.2%). During these leaching studies in seawater, arsenic was found to leach in both the pentavalent and trivalent oxidation state. The pentavalent state was predominant, comprising 77% of the arsenic initially desorbed.The dissolution in seawater of arsenic was utilized to assess the possible impact of the ocean disposal of fly ash. Based upon these data it appears that the natural levels of arsenic in the water column would not be significantly increased. Further research is needed on the fate of fly-ash particles in marine sediments.  相似文献   

9.
本文就渤海湾沉积物中总汞的分布特征、本底值及其污染状况等问题作一初步探讨。 一、材料及方法 1978年6月(枯水期)、9月(丰水期)两次在渤海湾40个测站用大样50型采泥器取表层样,为进一步了解汞自陆源入海后的扩散范围及污染过程,于1979—1980年在含汞较高的北  相似文献   

10.
Arsenic levels (up to 130 mg kg−1) substantially exceeding the official threshold have recently been documented in beach and nearshore sediments along more than 50 km of coastline in the Brazilian state of Espírito Santo between 19°50′ and 20°12′S. In an attempt to assess the sources of this enrichment, we performed a study on arsenic distribution in the main mineral substances and living organisms in the beach environment. Laboratory tests on arsenic retention by beach carbonate debris have also been carried out. The data suggest that sedimentary arsenic occurs largely bound to particles of the calcareous red alga Corallina panizzoi, whereby live specimens contained much smaller amounts of this metalloid than was the case for nonliving material (2.4 and 20.3 mg kg−1, respectively). Experimental tests confirmed the ability of C. panizzoi detritus to retain arsenic at pH intervals and ionic strength characteristic of seawater. There are two potential sources of that metalloid for calcareous debris in sediments: brown macroalgae, which were found to contain high levels of As (up to 66.3 mg kg−1), and ferruginized sandstones (up to 23.0 mg kg−1). We argue that any contribution of brown algae to beach sediment enrichment by As would be minor, and consider the ferrous sandstones from coastal sedimentary rocks of the Barreiras Group as the principal large-scale source of arsenic in the marine environment of Espírito Santo. The experimental data, together with field studies, corroborate the interpretation that arsenic anomalies in sediments with calcareous debris can form when weathered continental rocks even only slightly enriched in As are leached by marine waters, and the As is at least partially retained by biogenic calcareous detritus in nearshore sediments. Considering that rocks of the Barreiras Group are exposed to marine erosion far to the north of Espírito Santo, we estimate that marine sediments containing calcareous material are “anomalously” enriched in As along approximately 2,000 km of the Brazilian tropical coastline.  相似文献   

11.
Results of the radiochemical determination of 239+240Pu and 238Pu in seawater, plankton, marine organisms and sediment are reported. The samples were collected in the Taranto Gulf, and the data are compared with those obtained from other stations in the Mediterranean Sea. The vertical distribution of plutonium isotopes in sediments is also presented and discussed.  相似文献   

12.
Research of chromium speciation in the Bohai Gulf showed that content of particulate chromium in estuarine area rea ched more than 90%, so it is an existing dominant speciation in the Bohai Gulf. Ratio between trivalent chromium to total dissolved chromium is over 80%, whereas contents of hexavalent chromium is very low. The mean content of Cr (Ⅲ) is 5.6 times higher than that of Cr (Ⅵ). Thus trivalent chromium is the prinicipal speciation of valency state of chromium in the Bohai Gulf.Under the physical and chemical condition at the eatuary transferring mechanism of chromium in seawater of Bohai Gulf is done by absorption, complexion and subsequent settlement in the sediments of trivalent chromium by suspended matter. Therefore suspended matter plays a part on the purification of sewater for this gulf.  相似文献   

13.
90Sr,106Ru, natural strontium and major elements were studied in 12 samples of beach deposits from Togi, Fukuura and Shiga, and in 26 samples of shallow water sediments from sea off Fukuura, Noto Peninsula, Ishikawa Pref., Japan.The average contents of natural strontium and90Sr in the beach deposits were 488 ppm ranging from 247 to 1,550 ppm and 45±9 pCi kg–1-dry mud ranging from 18 to 72 pCi kg–1-dry mud, respectively. While the average contents of natural strontium,90Sr and106Ru in the sediments were 234 ppm ranging from 136 to 415 ppm, 22±6 pCi kg–1-dry sand ranging from 7 to 48 pCi kg–1-dry sand and 0.6 ±0.2 nCi kg–1-dry ranging from 0.3 to 1.2 nCi kg–1-dry, respectively.The average contents of each natural strontium and90Sr in the beach deposits were about two times higher than those in the shallow water sediments. But no obvious relation of natural strontium to90Sr was found in all the samples. The enrichment of90Sr and108Ru in the beach deposits or tthe sediments were as high as 150320 and of 2,0003,000 compared with average contents of90Sr and106Ru in a liter of surface water from the Japan Sea. It is to be noticed that the average106Ru to90Sr ratio of 27 for the shallow water sediments is much higher than the average of 1.0 for surface sea water of the Japan Sea.As to major elements of the samples, the beach deposits are rich in silicon (Av. 70.89 ±0.92% SiO2), but poor in iron (Av. 2.99±0.32% Fe2O3). Whereas the shallow water sediments are poor in silicon (Av. 52.96±10.33% SiO2) and rich in iron (Av. 5.50±1.90% Fe2O3), calcium (Av. 9.64±9.22% CaO) and magnesium (Av. 2.83±1.58% MgO).  相似文献   

14.
渤海中部沉积物铅来源的同位素示踪   总被引：1，自引：1，他引：0       下载免费PDF全文
本研究对渤海中部表层和柱状沉积物中Pb的含量和同位素进行了分析,研究了其时空分布规律,并探讨了其物质来源。结果表明,表层沉积物中Pb的含量为14.54×10-6~59.42×10-6,其含量在渤海湾近岸、黄河口附近、研究区的东北部较高,而在研究区的中部和渤海湾北部含量较低;Pb同位素207Pb/206Pb的值为0.8341~0.8489,208Pb/206Pb的值为2.0828~2.0980。岩心沉积物中Pb含量、同位素组成与表层沉积物相似,整体上较为稳定,但在1990s以来呈现增大的趋势。渤海中部沉积物中Pb以自然来源为主,黄河沉积物是其主要物质来源,但渤海湾北端则与滦河源物质或沿岸侵蚀相关;人类活动影响主要出现在1990s以后,与中国含Pb矿石的燃烧等工业活动相关,但影响微弱,仅在黄河口西北近岸海域、渤海湾等个别站位得到体现。  相似文献   

15.
A series of molecular organic markers were determined in surface sediments from the Gulf of Genoa (Ligurian Sea) in order to evaluate their potential for palaeo-environmental reconstructions. Allochthonous input can be characterized by the distributions of n-C29 and n-C31 alkanes, n-C26 and n-C28 alkanols and branched glycerol dialkyl glycerol tetraethers (GDGTs), whose concentrations are generally highest near the river mouths. In the open basin however, terrestrial n-alkanes and n-alkanols may have an additional, eolian source. Autochthonous input is represented by crenarchaeol and isoprenoid GDGTs. Their concentrations are highest in the open basin showing the preference of Thaumarchaeota for oligotrophic waters. Indications of a significant degradation of sterols and C37 alkenones exclude these lipids as reliable productivity proxies. Using terrestrial and aquatic lipids as end-members allows estimating the percentage of terrestrial organic matter between 20% and 58% in the coastal area decreasing to 1–30% in the deep basin. The spatial distribution of sea surface temperature (SST) estimates using the alkenone-based UK′37 index is very similar to the autumnal (November) mean satellite-based SST distribution. Conversely, TEXH86-derived SST estimates are close to winter SSTs in the coastal area and summer SSTs in the open basin. This pattern reflects presumably a shift in the main production of Thaumarchaeota from the coastal area in winter to the open basin in summer. This study represents a major prerequisite for the future application of lipid biomarkers on sediment cores from the Gulf of Genoa.  相似文献   

16.
Abstract

Seven sediment cores from the Palaea and Nea Kameni hydrothermal embayments (PK and NK) on Santorini have been studied by using sediment smear slides, X-ray diffraction, and radiocarbon techniques to determine their lithology, mineralogy, and age, respectively. The cores have been analyzed chemically for a suite of elements, including selective chemical leaching, to determine the partition of elements between coexisting phases. Lithologically and chemically, the sediments from the two embayments are very different. Sediments from PK are oxidized in the upper parts of the cores and reduced at depth; they comprise mainly hydrothermal pyritiferous diatomaceous ooze with minor Fe oxyhydroxide, volcanic debris, gypsum, and siderite. Sediments from NK are oxidized throughout and comprise predominantly amorphous iron oxyhydroxides and goethite; they are thought to have formed by direct precipitation from solution. In PK, biogenic, detrital seawater evaporate, and hydrothermal sediment phases have been identified but only the detrital inputs can be correlated between cores. Mn shows a pronounced enrichment towards the outer part of the embayment because of its dispersion down the embayment and precipitation in the more-oxidizing sediments towards the open sea. In NK, the sediments contain detrital, seawater evaporate, and hydrothermally precipitated and scavenged phases. The presence of substantial amounts of organic matter in the PK sediments but not in the NK sediments is probably the main reason why geochemical processes in the two embayments are different.

Age dates obtained from the cores by using the 14C technique indicate that sedimentation in the PK embayment commenced at ～ 50 AD, whereas in the NK embayment it commenced at ～ 1900 AD, which is consistent with the known history of Santorini. Based on these dates, calculated metal accumulation rates in both embayments are higher than in any other dated hydrothermal metalliferous sediments with the exception of those in the Atlantis II Deep of the Red Sea. Sediment ponding in the embayments is the principal cause of these results.  相似文献   

17.
By combining field observations with a statistical approach and a simple but effective estuarine analogue, the main features of the cycling of arsenic in the Tamar estuary have been elucidated. As(III) and As(V) enrichment in the water column is due to a combination of localized inputs and effective recycling of sediment interstitial waters. The profiles of As(V) are similar to those of NH4+ and are dominated by an estuarine maximum resulting from an input from the sediments. As(III) profiles are correlated with those of dissolved manganese and exhibit both fresh water and estuarine maxima. As(III) appears to be effectively removed at the freshwater/brackish water interface by a combination of heterogenous oxidation, catalysed by hydrous manganese dioxide, and adsorption on to iron oxyhydroxide. The estuarine distribution of As(III) within the water column is consistent with the published rates of oxidation of As(III) to As(V) by both inorganic and microbiological processes. The reduction of As(V) to As(III) in the sediments is incomplete. On the basis of our observations a tentative estuarine arsenic cycle is presented.  相似文献   

18.
Total arsenic, arsenate and arsenite concentration profiles for the water column of Saanich Inlet, an intermittently anoxic fjord located on Vancouver Island, B.C., Canada, were measured using independent analytical techniques for total arsenic and arsenic speciation to evaluate the accuracy of the speciation technique in both oxic and anoxic marine environments. Total arsenic profiles indicate a mid-depth minimum of about 1.0 ppb above the oxic—anoxic interface and an enrichment in the anoxic zone to about 2.0 ppb. This minimum may be due to either advection of arsenic-poor water into Saanich Inlet at mid-depth or arsenic incorporation onto solid phases within a bacteria- and manganese-rich particulate layer located immediately above the oxic—anoxic interface and subsequent removal via sinking particulate material. Ratios of total arsenic to phosphorus in the deep, anoxic waters of the basin are similar to those reported for marine algae, suggesting that the enrichment of total arsenic within the anoxic bottom layer may be due to its release upon organic matter decomposition.Arsenate and arsenite concentration versus depth profiles indicate a rapid (but incomplete in a thermodynamic sense) response to the oxic—anoxic interface. The arsenate/ arsenite concentration ratio is 15/1 in the oxic region of the water column and 1/12 in the anoxic zone. Arsenate—arsenite interconversion occurs at a depth shallower than ferric-ferrous but deeper than MnO2 —Mn2+ interconversions.Measurements of arsenite oxidation rates at near-ambient arsenite concentrations and temperatures using an 74As3+ radioactive tracer technique indicate that arsenite oxidation is initially ten times faster in seawater taken from the manganese-rich particulate layer at 165 m depth than in seawater collected near the surface at 50 m depth. Addition of antibiotics to seawater from 165 m depth initially suppressed the rate of arsenite oxidation, indicating that it may be partially microbially mediated.  相似文献   

19.
The interaction of Mn2+ with the surface of calcite in aqueous solutions is complex. In dilute solutions the Mn2+ is rapidly absorbed, MnCO33 nucleates on the calcite surface and then grows by a first order reaction with respect to the initial Mn2+ concentration. At higher ionic strengths in NaCl solutions, the rate of these processes is slower, but the same general pattern persists. In solutions containing Mg2+, at the concentration of seawater and in seawater, the nucleation phase of the uptake process does not appear to occur. The long-term uptake rate of Mn2+ on the surface of calcite in seawater is first order with respect to the dissolved Mn2+ concentration. The rate constant is over three orders of magnitude smaller than that found in dilute Mg2+-free solutions. A probable explanation for the slower growth rate in seawater is that MnCO3 is not nucleated on the calcite surface due to the presence of high Mg2+ concentrations. The Mg2+, through site competition, prevents enough Mn2+ from being adsorbed to reach a critical concentration for MnCO3 nucleation. This behavior is similar to that found for orthophosphate with calcite surfaces in dilute solutions and seawater. It indicates that rhodochrosite cannot nucleate in carbonate-rich recent sediments unless the Mg2+ concentration is lowered below that of seawater.Measurements of the solubility of rhodochrosite in seawater gave results from an undersaturation approach to equilibrium in excellent agreement with those found in previous studies in dilute solutions. When equilibrium was approached from supersaturation, approximately fifty times more calcium was precipitated than Mn2+. The measured solubility was over twice that determined from undersaturation. It is possible that a Mn—calcite containing 25 to 30 mol% MnCO3 formed on the rhodochrosite from the supersaturated solutions. Consequently, it is doubtful that pure rhodochrosite controls the concentration of Mn2+ even in calcium carbonate-poor marine environments.  相似文献   

20.
Organic-rich sediments and coexisting phosphorites from the continental shelf off South West Africa have been analysed for uranium and thiorum by alpha-spectrometry. The uranium concentrations in the sediments range from 10 to 55 ppm, with an isotopic composition close to that of sea-water, indicating that uranium is passing into the sediments at the present time. The phosphorites occur in the sediments as thin unconsolidated laminae and as lithified nodules and pellets, with uranium contents ranging from 79 to 158 ppm. Based on the uranium isotopic composition, only the unconsolidated phosphorite laminae are recent, while the lithified nodules and pellets, with 234U/238U and 230Th/234U ratios close to radio-active equilibrium, appear to be inherited from a previous period of phosphorite deposition. Deposition of uranium appears to take place predominantly by incorporation into carbonate fluorapatite growing authigenically within the sediment. Uranium accumulation rates, computed from 14C-dated sections of the sediment cores, and using only uranium values with modern isotopic composition, range from 232 to 765 μg/cm2 per 1,000 years. These results stress the importance of organic-rich sediments containing authigenic phosphorite beneath areas of high organic productivity as a major sink for uranium in the ocean.  相似文献   

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