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1.
The spatial and temporal variation in water-column respiration, estimated from enzymatic respiratory electron-transport-system activity, was measured monthly on a cross-shelf transect on the Louisiana shelf from May through October 1991. In July 1991, water-column respiration was also determined on an alongshore transect, and in situ benthic respiration and photosynthesis rates were determined at jour stations on the cross-shelf transect. Bottom waters were persistently hypoxic (O2<2 mg 1?1) at most stations in July and August and sporadically hypoxic at other times. Water-column respiration rates were in the same range as earlier, less extensive studies and not unusually high for coastal and estuarine waters. They were highest in summer, decreased with distance offshore and depth, and increased with temperature. Their variation with pigment and oxygen concentrations were complex functions of season and depth. Oxygen depletion below the oxycline could occur within days to months, depending on the season and location. In July, benthic respiration rates were also not unusually high in comparison with other shallow sediments, although the ratio of benthic: total (water column+benthic) respiration was high. Combined water-column and benthic respiration could deplete the bottom water oxygen in approximately 1 mo. Because the system rarely goes anoxic (defined as observing sulfide), some mechanism(s) must exist to reaerate bottom waters. Most physical mechanisms are unlikely to provide significant reaeration at this time of year. Measured benthic and conservatively estimated bottom-water photosynthesis could resupply 23% of the oxygen lost daily by respiration. Although this is too limited a dataset from which to draw conclusions about the relative importance of bottom-water and benthic respiration and photosynthesis in determining bottom-water oxygen concentrations, it does suggest that all these processes must be considered.  相似文献   

2.
《Applied Geochemistry》2001,16(1):95-108
Bottom sediments and suspended matter from the shelf and slope areas off northeastern Taiwan were analyzed for sterol, n-alkanol and n-alkane compositions. The Σ(algal sterols/cholesterol) ratios (mean±1σ) were 1.00±0.31 (n=7) for the shelf sediments, 3.29±0.61 (n=7) for the slope sediments, and 1.54±0.19 (n=3) for the suspended matter. The much higher proportion of cholesterol in the shelf sediments is most likely derived from mollusks in the relict sediments. An additional sterol source for the shelf sediments probably is suspended matter in the water column although the shelf has no apparent sedimentation. Results from phytol and n-alkanols suggest recent inputs of lipids from the water column to the shelf. The stanol/stenol ratios are lower for the older shelf sediments than for the younger slope sediments.  相似文献   

3.
Solid phase P speciation has been determined in sediments from a transect across the central section of the continental shelf and slope of the Great Barrier Reef (GBR) lagoon. This region is characterized by a gradient of riverine aluminosilicate clay and silt nearshore, seawards of which biogenic carbonate sediment predominates. Phosphorus speciation results show large variations along this transect. Organic P and authigenic (apatite) P are the major chemical forms of phosphorus in the central GBR continental shelf sediments. Post-depositional reorganization of P was also observed, converting organic P and iron bound P (Fe-P) to authigenic (apatite) P. Phosphorus burial rate was estimated from measurements of total P concentration and excess 210Pb sediment mass accumulation rates. Burial efficiency varies significantly over the shelf. Inshore areas showed significant P remobilization from sediments to the water column (up to ∼50%). The mid and the outer shelf showed little evidence for remobilization (except for coral reef platform sediments), with more of the sediment P being in the less reactive authigenic apatite phases. An appreciable fraction of this non-labile authigenic apatite phase was identified as fish bone. P sources and sinks over the central part of the GBR shelf were quantified using a mass balance approach. This showed that Coral Sea shelf edge upwelling events are essential to satisfy the large P nutrient demand of the whole GBR lagoon. P inputs due to upwelling events were greater than those contributed by local rivers over an average year.  相似文献   

4.
Investigation of chlorins in the oxic surface sediment of a small eutrophic alpine lake (Motte lake) revealed the presence of a new series of steryl chlorin esters containing the pheophorbide a nucleus, together with their pyropheophorbide a steryl ester counterparts previously observed in the anoxic surface sediment of the same lake. Identification of the pheophorbide a steryl esters was based on comparison of spectroscopic, chromatographic and mass spectrometric characteristics of the compounds with those of a synthetic standard and of pyropheophorbide a steryl esters. Combined liquid chromatography-mass spectrometry analysis confirmed the absence of pheophorbide a steryl esters in the anoxic sediment but allowed their detection in traces in the water column, indicating that pheophorbide a steryl esters are, like their pyropheophorbide a analogs, formed in the water column. The distribution of sterols released by hydrolysis of the pheophorbide a steryl esters shows close similarities to that of the free sterols in the water column and of the sterols of the pyropheophorbide a steryl esters. It appears that, like their pyropheophorbide a counterparts, pheophorbide a steryl esters incorporate mainly sterols of phytoplanktonic origin. Their formation probably involves the same mechanism as for pyropheophorbide a steryl ester formation, i.e. metabolism by zooplankton grazing on phytoplankton. The presence of pheophorbide a steryl esters in the oxic sediment and their absence from the anoxic sediment is probably due to a lower stability of compounds containing a carbomethoxy substituent in the anoxic environment.  相似文献   

5.
Total chlorins and carotenoids were measured in suspended paniculate matter, sediment trap, and zooplankton fecal pellet samples collected in the Peru upwelling region. Individual carotenoids were analyzed by high pressure liquid chromatography and mass spectrometry. Fucoxanthin, diadinoxanthin, diatoxanthin, carotene, and peridinin constitute > 95% of the total carotenoid pigments in suspended paniculate matter samples. However, sediment trap and zooplankton fecal pellet samples contained significant amounts of the carotenoid transformation products fucoxanthinol, fucoxanthin 5′-dehydrate, fucoxanthinol 5′-dehydrate, peridininol and peridininol 5′-dehydrate. These samples were further characterized by high values of the ratio fucoxanthinol/total fucopigments (f/Ft) and low values of the ratio total carotenoids /total chlorins. Three reactions are proposed to account for the formation of observed products: heterotrophic ester hydrolysis, chemically mediated epoxide rearrangement, and microbially mediated dehydration. The distribution of specific transformation products within the samples suggests that heterotrophic ester hydrolysis is a general transformation pathway operative in the water column on a wide suite of organic esters. Epoxide rearrangement and dehydration appear to occur over a longer time scale and are more typical of sedimentary environments.  相似文献   

6.
No pre-1977 quantitative data exist that describe phytoplankton biomass in the water column of Lake Suwa, a Japanese eutrophic lake, although several studies have been conducted since. To assess recent environmental changes with time in the lake, phytoplankton composition was determined from analysis of photosynthetic pigments in the sediment core. Specifically, the total chlorophyll a (TCh-a) concentration in the water column before 1977 was estimated for comparison with that of the water column and sediment deposited since 1977. The depth profile of zeaxanthin, a potential indicator of cyanobacteria activity, substantially increased from 1960 to 1973 (from 9.53 to 76.7?nmol?g?1). Additionally, the concentration of fucoxanthin, diadinoxanthin and diatoxanthin, originating from diatoms and dinoflagellates, increased slightly during this period (from 1.64 to 4.90, 1.86 to 3.54, and 4.00 to 3.26?nmol?g?1). Cyanobacteria have been the major algal species in the lake since 1949; however, the ratio of fucoxanthin versus total algal carotenoids has gradually increased since 1981 indicating diatoms have increased relative to cyanobacteria since 1979, and that organic matter inflow and nutrient concentrations have resulted in changes in the phytoplankton composition. Since 1977, the chlorophyll a concentration in water in the lake had a very similar pattern as the TCh-a concentration in the sediment. The concentration in the water column also corresponds to those in the sediment even before 1977. These results indicate that it might be possible to predict the phytoplankton biomass of the water column based on the TCh-a in the water and sediment in this lake.  相似文献   

7.
Continental shelf sediments from nine locations off Washington and Oregon have 239,240Pu inventories which average 8.0 ± 2.6 mCi/km2. The Columbia River and seawaters advecting over the shelf supply Pu which is removed to underlying sediments, principally through scavenging by inorganic paniculate matter. Mass balance calculations argue that less than 20 percent of the advected Pu need be scavenged from the water column to balance river input and total shelf sediment inventories. The percentage of the Pu removed through scavenging is consistent with observed participate concentrations in shelf waters and published sediment/water distribution coefficients.No marked separation of Pu from 137Cs is observed with depth in Pacific shelf sediments as has been reported in Atlantic coastal sediments. This interocean distinctness can be explained by differences in particle mixing and downward diffusion of Cs in sediments of varying porosities. The transuranic inventories and Pu/Cs ratios in the Pacific sediments do not support the hypothesis of Livingston and Bowen that Pu is remobilized within the sediment column by ‘complexone’ formation with (principally) organic substances.Excess 210Pb/239,240Pu inventory ratios in eight representative cores from the Washington shelf average 100 ± 19, even though absolute values of both inventories vary by much larger factors. This reasonably constant ratio, for a given water depth, permits estimation of total Pu inventories and prediction of sites of unusual Pu accumulation from data on the more easily measured natural radionuclide.  相似文献   

8.
Chlorophyll degradation products are preserved in marine sediments over timescales of thousands of years. The production of chlorophyll in the water column is related to biological productivity, so chlorophyll degradation products (chlorins) preserved in marine sediments can be used as indicators of paleoproductivity. A new, rapid, non-destructive method of determining chlorin concentrations in marine sediments is presented. Potential interferences associated with the solid-phase fluorescence (SPF) method are explored using reference materials, yet this method compares favorably with spectroscopic and high performance liquid chromatographic (HPLC) methods of analysis using marine sediments from Boston Harbor and the continental shelf off northwest Africa.  相似文献   

9.
Suspended sediments (SS) from the Atchafalaya River (AR) and the Mississippi River and surficial sediment samples from seven shallow cross-shelf transects west of the AR in the northern Gulf of Mexico were examined using elemental (%OC, C/N), isotopic (δ13C, Δ14C), and terrigenous biomarker analyses. The organic matter (OM) delivered by the AR is isotopically enriched (∼−24.5‰) and relatively degraded, suggesting that soil-derived OM with a C4 signature is the predominant OM source for these SS. The shelf sediments display OC values that generally decrease seaward within each transect and westward, parallel to the coastline. A strong terrigenous C/N (29) signal is observed in sediments deposited close to the mouth of the river, but values along the remainder of the shelf fall within a narrow range (8-13), with no apparent offshore trends. Depleted stable carbon isotope (δ13C) values typical of C3 plant debris (−27‰) are found near the river mouth and become more enriched (−22 to −21‰) offshore. The spatial distribution of lignin in shelf sediments mirrors that of OC, with high lignin yields found inshore relative to that found offshore (water depth > 10 m).The isotopic and biomarker data indicate that at least two types of terrigenous OM are deposited within the study area. Relatively undegraded, C3 plant debris is deposited close to the mouth of the AR, whereas more degraded, isotopically enriched, soil-derived OM appears to be deposited along the remainder of the shelf. An important input from marine carbon is found at the stations offshore from the 10-m isobath. Quantification of the terrigenous component of sedimentary OM is complicated by the heterogeneous composition of the terrigenous end-member. A three-end-member mixing model is therefore required to more accurately evaluate the sources of OM deposited in the study area. The results of the mixing calculation indicate that terrigenous OM (soil-derived OM and vascular plant debris) accounts for ∼79% of the OM deposited as inshore sediments and 66% of OM deposited as offshore sediments. Importantly, the abundance of terrigenous OM is 40% higher in inshore sediments and nearly 85% higher in offshore sediments than indicated by a two-end-member mixing model. Such a result highlights the need to reevaluate the inputs and cycling of soil-derived OM in the coastal ocean.  相似文献   

10.
Many Gulf of Mexico estuaries have low ratios of water volume to bottom surface area, and benthic processes in these systems likely have a major influence on system structure and function. The purpose of this study was to determine the spatiotemporal distribution of biomass and community composition of subtidal benthic microalgal (BMA) communities in Galveston Bay, TX, USA, compare BMA community composition and biomass to phytoplankton in overlying waters, and estimate the potential contribution of BMA to the trophodynamics in this shallow, turbid, subtropical estuary. The estimates of BMA biomass (mean = 4.21 mg Chl a m−2) for Galveston Bay were within the range of the reported values for similar Gulf of Mexico estuaries. BMA biomass in the central part of the bay was essentially homogeneous, whereas biomass at the seaward and upper bay ends of the transect were significantly lower. Peridinin, fucoxanthin, and alloxanthin were the three carotenoids with the highest concentrations, with fucoxanthin having the highest mean concentration (1.82 mg m−2). The seaward and landward ends of the transect differed from the central region of the bay with respect to the relative abundances of chlorophytes, cyanobacteria, and photosynthetic bacteria. Benthic microalgal community composition also showed a gradual shift over time due to changes in the relative abundances of photosynthetic bacteria, cryptophytes, dinoflagellates, and cyanobacteria. Major changes in community composition occurred in the spring months (March to April). On an areal basis, BMA biomass in Galveston Bay occurred at minor concentrations (16.5%) relative to phytoplankton. Furthermore, the concentrations of carotenoid pigments for phytoplankton and BMA (fucoxanthin, alloxanthin, and zeaxanthin) were correlated (r = 0.48 to 0.61), suggesting a close linkage between microalgae in the water column and sediments. The contribution of BMA to the primary productivity of the deeper waters (>2 m) of Galveston Bay is probably very small in comparison to shallower waters along the bay margins. The significant similarities in the community composition of phytoplankton and BMA illustrate the potential importance of deposition and resuspension processes in this turbid, shallow estuary.  相似文献   

11.
This paper provides insight into the fate of Late Weichselian and Early Holocene sediments accumulated in the German sector of the southern North Sea. A combination of optically stimulated luminescence (OSL) dating and radiocarbon dating was applied to set up the chronology. Seven cores were studied to obtain ten quartz OSL samples and ten radiocarbon samples. The core locations were chosen along a southeast to northwest transect along the western side of the Elbe palaeovalley, giving a good coverage of the entire German North Sea area. All samples for OSL dating showed a significant scatter in the equivalent dose (De) distribution of quartz due to heterogeneous bleaching. The Minimum Age Model (MAM-3) was found to be the most suitable to extract true burial ages. It was inferred from the study that sedimentation did still occur during the late deglaciation period in many areas. These are mainly Late Weichselian glaciofluvial or glaciolacustrine sediments directly overlain by early Holocene fluvial and/or transgressive deposits and followed by modern marine sands. However, considerable late Weichselian erosion or a possible period of non-deposition was observed in the highland area to the northeast of the Dogger Bank and a small discontinuity in the near-shore region was noticed, probably due to early Holocene fluvial erosion. Relicts of a palaeo-river bank or terrace were identified in core 14VC to the east of the Dogger Bank. A possible interpretation of the Pleistocene-Holocene interface along the core transect is provided based on lithology and measured OSL and radiocarbon ages.  相似文献   

12.
《Chemical Geology》2002,182(2-4):377-394
Bulk heavy metal (Fe, Mn, Zn, Cu, Pb, Cd), Al, organic carbon and carbonate concentrations, grain sizes, and δC13 of the organic carbon distributions were studied in sediments collected throughout the East China Sea continental shelf and the Yangtze River Delta. The results demonstrated that terrigenous sediments from the Yangtze River is a dominating factor controlling the spatial variations of heavy metals and organic carbon concentrations on the East China Sea continental shelf. In addition, grain size and recent anthropogenic influences are also major factors modifying the spatial and vertical variations of heavy metals.Large spatial variations with a band type distribution of heavy metals, grain size, organic carbon and carbonate were observed. Higher concentrations of heavy metal and light δC13 of the organic carbon were found primarily in the Deltaic and inner shelf sediments. The band type distribution generally followed the coastline with little variations in the north–south direction. Away from the Delta and inner shelf (west–east direction), most heavy metal concentrations decreased rapidly with the exception of Cd where high concentrations of Cd were also found in the carbonate-rich shelf break sediments. Coarse-grained relict sediments and biogenic carbonate are two primary diluting agents for the fine-grained aluminosilicate sediments from the Yangtze River with high concentrations of heavy metals.Unusually high concentrations of Cu, Pb, and Cd showed both spatially and vertically that more pollution prevention measures are needed in the Yangtze River drainage basin in order to prevent further heavy metal pollution of the East China Sea inner continental shelf.  相似文献   

13.
In Amazon-shelf waters, as salinity increases to 36.5 × 10−3, dissolved uranium activities increase to a maximum of 4.60 dpm 1−1. This value is much higher than the open-ocean value (2.50 dpm 1−1), indicating a source of dissolved uranium to shelf waters in addition to that supplied from open-ocean and riverine waters. Uranium activities are much lower for surface sediments in the Amazon-shelf seabed (mean: 0.69 ±.09 dpm g−1) than for suspended sediments in the Amazon River (1.82 dpm g−1). Data suggest that the loss of particulate uranium from riverine sediments (and the consequent input of dissolved uranium to shelf waters) is probably the result of uranium desorption from the ferric-oxyhydroxide coatings on sediment particles, and/or uranium release by mobilization of the ferric oxyhydroxides. The total flux (i.e., riverine flux plus desorbed-remobilized particulate flux) of dissolved 238U from the Amazon shelf (about 1.2 × 1015 dpm yr−1) constitutes about 15% of uranium input to the world ocean, commensurate to the Amazon River's contribution to world river-water discharge (approximately 18%). Measurement of only the riverine flux of dissolved 238U underestimates, by a factor of about 5, the flux of dissolved238U from the Amazon shelf to the open ocean.  相似文献   

14.
Exposure of humans to monomethylmercury (MMHg) occurs primarily through consumption of marine fish, yet there is limited understanding concerning the bioaccumulation and biogeochemistry of MMHg in the biologically productive coastal ocean. We examined the cycling of MMHg in sediments at three locations on the continental shelf of southern New England in September 2003. MMHg in surface sediments is related positively to inorganic Hg (Hg(II) = total Hg − MMHg), the geographical distribution of which is influenced by organic material. Organic matter also largely controls the sediment-water partitioning of Hg species and governs the availability of dissolved Hg(II) for methylation. Potential gross rates of MMHg production, assayed by experimental addition of 200Hg to intact sediment cores, are correlated inversely with the distribution coefficient (KD) of Hg(II) and positively with the concentration of Hg(II), most probably as HgS0, in 0.2-μm filtered pore water of these low-sulfide deposits. Moreover, the efflux of dissolved MMHg to overlying water (i.e., net production at steady state) is correlated with the gross potential rate of MMHg production in surface sediments. These results suggest that the production and efflux of MMHg from coastal marine sediments is limited by Hg(II), loadings of which presumably are principally from atmospheric deposition to this region of the continental shelf. The estimated diffusive flux of MMHg from the shelf sediments averages 9 pmol m−2 d−1. This flux is comparable to that required to sustain the current rate of MMHg accumulation by marine fish, and may be enhanced by the efflux of MMHg from near-shore deposits contaminated more substantially with anthropogenic Hg. Hence, production and subsequent mobilization of MMHg from sediments in the coastal zone may be a major source of MMHg to the ocean and marine biota, including fishes consumed by humans.  相似文献   

15.
《Quaternary Science Reviews》2007,26(19-21):2406-2419
Glaciated continental shelves are characterised by large amphitheatre-like embayments between prominent cross-shelf troughs. The integration of swath bathymetry and high-resolution seismic data (3D, 2D) collected across the western Svalbard continental margin indicates how such embayments form. Although their bathymetric expression resembles headwall scarps of submarine slope failures, the shelf embayments are the result of the interplay between sediment dynamics and transport underneath fast-moving ice streams in the cross-shelf troughs and the slower-moving parts of the ice sheets on the adjacent shallower shelf banks during full glacial conditions. This is supported by (1) the absence of major landslide deposits at their toe, (2) continuous prograding shelf deposition and (3) absence of landslide-related faulting. Instead, the seismic data suggest a depositional origin of the shelf embayments that is characterised by continuous sediment input at lower rates off a slow-moving ice mass in the centre of the embayment which is fringed by the lateral ice-stream ridges. These findings put into perspective the importance of submarine slope failure on glaciated margins.  相似文献   

16.
Eighty-six surface sediments collected from the northwestern continental shelf of the South China Sea (SCS) were analyzed for grain size distribution, calcium carbonate, organic carbon, and major and trace element compositions to investigate sediment provenance and factors controlling their geochemical composition. Sediments from the eastern continental shelf of Hainan Island have higher sand and lower clay content, while the samples from the nearshore Hainan Island have higher contents of gravel and clay. Calcium carbonate contents in samples show a positive correlation with water depth in northwestern shelf of SCS, suggesting that it is related to biological factors. However, the nearshore sediments have higher contents of organic carbon compared to those of the outer shelf, possibly suggesting that the terrigenous organic matter usually deposited in nearshore environments such as bays and estuaries. Compared with the upper continental crust, the samples have relatively lower contents of SiO2 and Al2O3, higher than those of the Pearl and Red river sediments. The low contents of K2O and Na2O in sediments from the northwestern continental shelf are consistent with intense chemical weathering in the river basin due to the seasonally hot and humid climate regime. The sediments mainly consist of three components, including the gravel fraction composed of calcareous debris, the sand fraction composed of quartz, and the silt and clay fractions mainly composed of clay minerals. The content of each component depends on grain size, sediment source, biogenesis, and hydrodynamic conditions, which finally controls the chemical composition of the sediments. The distributions of Co/Al2O3, Cr/Al2O3, and Zr/Sc ratios for sediments in the northwestern continental shelf suggest that source rocks are mainly composed of felsic rocks rather than mafic rocks. There is a distinct difference in sediment source between eastern and western shelf sediments; the eastern shelf sediments are characterized by high Zr/Sc ratios mainly derived from the Pearl River, while the western shelf sediments have relatively low values of Zr/Sc indicating a main contribution possibly sourced from the Red River Basin. Terrigenous materials from Hainan Island usually influence the geochemistry of sediments deposited in the nearshore area.  相似文献   

17.
Aragonite and calcite needles, 30–500 μm long, were found to be prominent visual components throughout the water column in some areas of the New England (northeastern U.S.A.) continental shelf during winter months. Further investigation showed these‘needles’to be laths derived from the degradation of mollusc shells which were resuspended from bottom sediments during winter storms. Such degradation and subsequent transport/dissolution of carbonate particles may help explain why the terrigenous 'starved’shelf sediments off New England contain such small amounts of calcium carbonate.  相似文献   

18.
Extensive portions of the continental shelf off the coast of British Columbia were subaerially exposed during Late Wisconsinan deglaciation due to lowering of relative sea level by as much as 150 m. Paleoecological analyses were conducted at two sites on the emergent continental shelf where terrestrial surfaces with in situ conifers are preserved. The woody plant remains confirm that, during the latest period of subaerial exposure, terrestrial vegetation was established on the continental shelf. Microscopic identification of fossil wood, and analyses of pollen and plant macrofossils from the associated paleosols and overlying shallow pond sediments indicate that productive Pinus contorta-dominated communities with abundant Alnus crispa and ferns grew on the shelf adjacent to and on the Queen Charlotte Islands around 12,200 14C yr B.P. Dwarf shrubs including Salix and Empetrum, and herbaceous plants such as Heracleum lanatum and Hippuris vulgaris, were also important components of the shelf vegetation. Near northern Vancouver Island, mixed coniferous forests dominated by Pinus contorta with Picea, Tsuga spp., Alnus spp., and ferns occupied the shelf at 10,500 14C yr B.P.  相似文献   

19.
The vertical distribution of iodine, bromine and organic carbon has been examined in sediment cores from a range of environments on the Namibian shelf. The relationship between Br and C org. is linear, and that between I and C org. is variable, for all surface sediments; I/C org. ratios show a decrease of about one order of magnitude between the outer shelf oxidising sediments (250 × 10?4) and the organic-rich inner shelf sediments (20 × 10?4). The contrasting behaviour of the halogens in surface sediments is explained by differences in the amount of halogen absorbed by living organisms within the euphotic zone and on seston on the seabed. It is suggested that sorption by seston occurs only in oxidising sediment where free O2 is available. Hence, iodine is sorbed by seston in the outer shelf environment, but is not sorbed by the reducing sediments of the inner shelf. Here the iodine in the sediment represents only that taken up by plankton. On the outer shelf, 50–80% of the total iodine in the organic matter is sorbed by seston. The principal site of Br uptake is not known.The distribution of C org. in subsurface sediments broadly reflects that found at the surface, although there is a slight decrease with depth in the outer shelf cores due to dilution by terrigenous materials. In the inner shelf cores, there is no change in the relationship of iodine and bromine to organic carbon at depth. Those from the mid shelf, and especially the outer shelf, on the other hand, show decreases in both I/C org. and Br/C org. ratios, reaching values at about 70 cm depth that are similar to those in surface reduced sediments from the inner shelf. Over this depth interval I/C org. ratios decrease by a factor of five while Br/C org. ratios show a two fold decrease. These changes in the ratios at depth imply that diagenesis within the reducing cores is negligible compared with that of oxidised sediments. The implications of diagenesis with regard to halogen recycling in sediments are briefly discussed.  相似文献   

20.
Hydrocarbon gases (methane, ethane, ethene, propane, propene, isobutane and n-butane) are present in low concentrations in the top two meters of sediment from the shelf, slope and basin of the Bering Sea. Methane is most abundant and its concentration increases with depth in the sediment. Average concentrations of methane recovered from these sediments are between about 4000 and 5000 nl per 1 of interstitial water. Ethane, ethene, propane and propene are present in almost all samples, but the concentrations of these gases are about two orders of magnitude lower than the concentration of methane. The average ratios of ethane to ethene are usually greater than one in shelf sediment, about one in slope sediment, and usually less than one in basin sediments. These hydrocarbon gases are probably derived from low-temperature chemical and biochemical processes operating at or near the sea-floor. At one location on the shelf, hydrocarbon gases suggest the possibility of petroleum at depth.  相似文献   

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