首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 500 毫秒
1.
Both water and suspended particulate matter in the deep water of the Gulf of St. Lawrence are greatly enriched in manganese. Maximum dissolved manganese concentrations are encountered close to the sediment-water interface whereas the particulate matter with highest manganese content occurs 30–100 m above the bottom. The elevated concentrations are attributed to the diagenetic release of dissolved manganese from the underlying fine-grained sediments and its subsequent precipitation in the water column. The rate of manganese precipitation is rapid compared to the rates of diffusion and mixing in the bottom water. Part of the manganese-enriched particulate matter becomes mixed throughout the water column by advection and diffusion. Thus, particles enriched in manganese can ultimately be carried into the open ocean by prevailing currents. This process, which appears to be widespread in eastern Canadian coastal waters, enables manganese originally associated with rapidly settling terrigenous particles to be transferred to slowly settling fine-grained suspended particles entering the ocean from coastal environments. In this way, riverborne manganese of terrigenous origin may well account for a major proportion of the excess manganese in pelagic sediments.  相似文献   

2.
Between 1980 and 1984 extensive studies were carried out in the Baltic Sea on trace metals (Cd, Co, Cu, Fe, Hg, Mn, Ni, Pb and Zn) in water, suspended matter and sediments. The results enabled the influence of different factors on metal distribution patterns to be considered. The vertical profiles of dissolved and particulate metals in waters of the central deep basins reflect influences caused by oxygen deficiency and anoxic conditions in near-bottom water layers. Peculiarities at Station BY15 in the Gotland Deep included high dissolved Fe, Mn and Co concentrations and remarkable enrichment of Zn (0.64%), Cd (51 μg g−1) and Cu (0.15%) in particulate matter from the anoxic zone. Manganese-rich particles were accumulated above this layer.In fine-grained soft sediments below anoxic deep waters, maximum contents of Cd, Cu and Zn were observed, relative to other coring sites, between Bothnian Bay and Lübeck Bight. The Hg content in sediments probably reflects the joint flocculation with organic matter. Land-based sources seem to play the leading part for maximum lead contents.  相似文献   

3.
Dissolved and total dissolvable manganese concentrations have been measured at four stations in the western North Atlantic Ocean. Total dissolvable manganese concentrations are high in surface waters, decrease to uniformly low levels throughout the bulk of the water column, and increase in the bottom nepheloid layer. Dissolved Mn (Mnd) concentrations follow the total dissolvable concentrations throughout the surface and deep waters but do not increase in the near-bottom waters.Deep water concentrations of Mnd decrease from 30 ng l?1 in the Newfoundland Basin to 20 ng l?1 in the Sargasso Sea. This change and other features of the deep water distribution of dissolved manganese could be associated with the slow oxidation of Mn2+ to MnO2. There is also evidence at one station of scavenging of manganese from the dissolved phase in the near-bottom layer which may again be related to the kinetics of manganese oxidation.  相似文献   

4.
1 Indroduction The coastal zone and continental shelf area is an important region in the global biogeochemical cycle of nutrients in the ocean. This portion of the global ocean interacts closely with the continents, atmosphere and the open ocean in a comp…  相似文献   

5.
The distributions of dissolved and solid phase Fe and Mn have been variously determined in vertical profiles through the water column and sediments at three stations in Bolstadfjord, S.W. Norway. Elevated concentrations of dissolved and suspended particulate Fe and Mn are associated with restricted deep waters as a result of redox reactions and with river discharge. The basin sediments are anoxic throughout but because of the greatly restricted circulation, remobilized Fe and Mn appear to remain predominantly trapped within the fjord. Differentiation of Fe and Mn occurs to the extent that Fe sulphide precipitation is ubiquitous in the sediments whereas the entrapment of Mn, probably through Mn carbonate precipitation, is found only in the sediments of the more seaward basin (maximum Mn content of 1·5% by weight).  相似文献   

6.
Depth profiles of the naturally-occurring radionuclides 238U, 234U, 226Ra, 228Ra and 228Th were obtained in two diverse anoxic marine environments; the permanently anoxic Framvaren Fjord in southern Norway and the intermittently anoxic Saanich Inlet in British Columbia. Concentrations of total H2S were over three orders of magnitude greater in the anoxic bottom waters of Framvaren Fjord compared to those in Saanich Inlet.In Framvaren Fjord, the O2/H2S interface was located at 17 m. While dissolved 238U behaved conservatively throughout the oxic and anoxic water columns, concentrations based on the 238U/salinity ratio in oxic oceanic waters were almost 30% lower. Dissolved 226Ra displayed a sharp maximum just below the O2/H2S interface, coinciding with dissolved Mn (II) and Fe (II) maxima in this zone. It is suggested that reductive dissolution of Fe-Mn oxyhydroxides remobilizes 226Ra in this region.In Saanich Inlet, the O2/H2S interface was located at 175 m. Dissolved 238U displayed a strongly nonconservative distribution. The depth profiles of dissolved 226Ra and 228Th correlated well with the distribution of dissolved Mn (II) in the suboxic waters above the O2/H2S interface, suggesting that reduction of particulate Mn regulates the behavior of 226Ra and 228Th in this region.Removal residence times for dissolved 228Th in the surface oxic waters of both systems are longer than those generally reported for particle-reactive radionuclides in coastal marine environments. In the anoxic waters of Framvaren Fjord and Saanich Inlet, however, the dissolved 228Th removal residence times are quite similar to values reported for dissolved 210Pb in the anoxic waters of the Cariaco Trench and the Orca Basin. This implies that the geochemistries of Th and Pb may be similar in anoxic marine waters.  相似文献   

7.
In September 2008, freshening of near-bottom water and an increase in concentration of suspended particles were observed in the western part of southern Lake Baikal. The reduction in the content of total dissolved solids was about 0.4–0.7?mg/kg (0.7?%), and average suspended particle concentration increased strongly to 6–9?mg/l, the background value being 0.2?mg/l. The spatial distribution of these waters was virtually identical to the focal area of the Mw6.2 Kultuk earthquake that occurred on 27 August 2008. It is suggested that there was a causal relationship between these two phenomena. Freshening of a significant amount (about 20?km3) of near-bottom waters was plausibly caused by an input of poorly mineralized pore waters from bottom sediments as a result of dissociation of methane gas hydrates suspected to occur in the area. The energy radiated by the earthquake source was four orders of magnitude smaller than that needed to explain the observed freshening of near-bottom waters. This points to other mechanisms leading to seismic-induced sediment failure and possible subsequent hydrate dissociation in the case of the Kultuk earthquake.  相似文献   

8.
The intense halocline and redoxcline in the Orca Basin, northwest Gulf of Mexico, induce dramatic water column profiles for manganese, iron, and suspended particulates. Within a 17 m interval, the salinity of the basin water increases from 66 to 260 & permil and dissolved oxygen decreases to zero. Midway through this transition zone, concentrations of suspended matter peak at 900 g/liter. Dissolved iron and manganese concentrations in the anoxic brine increase from oceanic values to maxima of 1.6 and 22 mg/liter, respectively. Upward migration of dissolved manganese from the brine leads to production of manganese-rich particles in the slightly oxygenated overlying water.  相似文献   

9.
The Mackenzie River estuary serves as an avenue for suspended particles to pass seaward. The horizontal distribution of surface suspended particles is compartible with the distribution of low-salinity surface waters. The water structure in the shelf area is highly stratified in summer due to a thin upper layer of low-salinity which has a high concentration of suspended particles. The concentration of suspended particles decreases with depth, but near the bottom a turbid layer had often been observed. It is likely that bottom current energy high enough to erode and maintain in suspension the bottom sediments below 15m in diameter does occur over this shelf area.  相似文献   

10.
Concentrations of dissolved iron, manganese, molybdenum, copper, and organic carbon (DOC) were measured in the pore waters from surficial sediments of a temperate estuary to delineate seasonal metal remobilization from 1978 through 1980. Iron and DOC data were collected for 31 months and covaried inversely and exponentially. Iron dissolution occurred during the spring and during periods of active bioturbation with concentrations as high as 18 mg 1?1. Iron values were low during winter due to oxidation to ferric oxides. The lack of active bioturbation during the summer of 1978 allowed for the nearly complete removal of iron as a monosulfide precipitate. However, bioturbation resumed during the summer of 1979 and 1980 and dissolved iron concentrations as high as 10 mg 1?1 were observed at those times. The iron and DOC data were a qualitative measure of bioturbation activity. Dissolved manganese, molybdenum, and copper data were collected for 18 months during 1978 and 1979. All three metals displayed spring maxima covariate with iron, suggesting that they behaved chemically like iron and/or were associated with iron- or manganese-rich phases during this time of the year. In general, manganese and molybdenum varied temporally with iron while copper concentrations mimicked iron variations only during the spring.  相似文献   

11.
Vertical and horizontal distributions of manganese in Harima Sound (Harima Nada, Seto Inland Sea) were measured in August and December 1979. High concentrations of dissolved and particulate manganese were found in bottom waters in August, suggesting that the bottom enrichment is probably due to the diffusion of dissolved manganese out of the sediment. From measured distributions, we estimate the annual flux of manganese at the sediment-water interface to be more than 800 tons per year, if Harima Sound is a closed system for manganese.  相似文献   

12.
Research has been conducted in Nha Trang Bay (Southern Vietnam, the South China Sea) at the section from the estuary of the Cai River to the marine part of the bay, as well as in the area of coral reefs. The objects of the studies are the river and sea waters, the suspended matter, and the bottom sediments. Data on the dissolved organic carbon and the total nitrogen in the water are obtained. The organic carbon content is estimated in the suspended matter; the organic carbon and the molecular and group composition of the n-alkanes are determined in the bottom sediments. The molecular and group composition of the n-alkanes in the bottom sediments of the landfill have made it possible to identify three types of organic matter (OM): marine, mixed, and of mainly terrigenous origin. All the types of OM are closely related to the specificity of the sedimentation and the hydrodynamics of the waters in this water area.  相似文献   

13.
The high diversity of grain-size parameters of marine and oceanic sediments is determined by hydrodynamical and gravitational processes. Grain-size spectra of the sediments in the World Ocean are represented by two main types. Filtering organisms that passively inherit the proportions of clayey fractions in suspended matter only accelerate the deposition of fine particles, not influencing their distribution at the bottom.  相似文献   

14.
《Marine Chemistry》2001,73(1):21-36
As part of the ANTARES 3/F-JGOFS cruise, the distributions of dissolved iron and manganese were measured in October 1995 in the north–east wake of the Kerguelen archipelago (48°40′–49°40′S, 68°70′–70°50′E), an area that shows high phytoplankton biomass (CZCS and SeaWiFS data) in the middle of the High Nutrient Low Chlorophyll (HNLC) Southern Ocean. The study area (about 25,000 km2) comprised a branch of the Polar Front with Antarctic surface water (AASW) intruding northward, shouldering the shelf break of the Kerguelen Plateau. The coastal zone was clearly affected by material of lithogenic origin (riverine discharges, soil leaching by rain waters, aeolian inputs), as well as by inputs from the sediments (effluxes from the sediment–water interface, resuspension from the sediments), its near surface waters showing considerable enrichment in dissolved iron (5.3–12.6 nM) and in dissolved manganese (2.9–8.6 nM). The offshore waters, although less enriched in trace-metals, were also affected by trace-metal inputs from coastal and continental shelf origin. Dissolved iron and manganese concentrations in these waters were 0.46–0.71 and 0.68–1.3 nM, i.e. far over typical antarctic open ocean surface water concentrations of 0.16 nM for iron [Martin, J.H., Gordon, R.M., Fitzwater, S.E., 1990. Iron in Antarctic waters. Nature, 345: 156–158.] and around 0.1 nM for manganese [Martin, J.H., Gordon, R.M., Fitzwater, S.E., 1990. Iron in Antarctic waters. Nature, 345: 156–158; Sedwick, P.N., Edwards, P.R., Mackey, D.J., Griffiths, F.B., Parslow, J.S., 1997. Iron and manganese in surface waters of the Australian subantarctic region. Deep-Sea Res., 44: 1239–1253.]. The dissolved iron enrichment in coastal waters of the Kerguelen Islands is much more important (about 10 times for dissolved iron) than for the Galapagos Islands, another oasis in the HNLC Equatorial oceanic system, where the concentration increase in dissolved iron in the surface waters around the islands is mostly driven by upwelling of the Equatorial Under Current (EUC) as it reaches the Galapagos Platform.  相似文献   

15.
Numerous oceanographic cruises (with hydrology, water sampling, drift current measurements) carried out since 1980 on the continental shelf of the Bay of Biscay, together with available NOAA/AVHRR infra-red images, form the basis of a proposed explanation for the processes responsible for the distribution of suspended sediments on the shelf. The seasonal hydrographic structure of continental shelf waters is of paramount importance in sediment distribution. In summer, there is an horizontal stratification of water masses, and suspended sediment distribution is closely related to the thermo-haline structure. A fresher water mass with less suspended material lies on a thicker and more turbid homogeneous layer. During winter, when sediment discharge from the rivers often reaches its annual maximum, an oceanic thermo-haline wedge occurs on the shelf at around −100 m. As a result, winter turbidity values on the outer continental shelf are low (comparable to summer values), and a permanent nepheloı̈d layer is never observed. The wedge, which lasts for several months, may act as a filter, preventing transport to the slope. High turbidities on the external shelf and the continental slope are only measured in spring, when the thermo-haline wedge disappears. It seems possible that during winter time, suspended materials brought by rivers are deposited in the “Grande Vasière” (the “large mud patch”). It is postulated that the position of this mud patch is linked to the long-term stable location of the thermo-haline front that separates oceanic waters from the colder and less salty coastal waters.  相似文献   

16.
Water column samples have been collected in the outer channel of the Ferrol Ria (NW Spain) during four occasions over a tidal cycle. The objective was to study the exchange of dissolved and particulate Cd, Cu, Pb and Zn and particulate Al, Fe and Si between the ria and the adjacent coastal waters. This study provides the first extensive dataset on dissolved and particulate metal concentrations in the water column of a Galician ria. Typical concentrations of dissolved Cd (96 ± 31 pM), Cu (8 ± 4 nM), Pb (270 ± 170 pM) and Zn (21 ± 10 nM) were similar than in other European Atlantic shelf and coastal waters. The fraction of metals in the particulate phase followed the trend: Pb > Cu Zn > Cd. The outgoing water from the ria was enriched in dissolved and particulate Cu, Pb and Zn compared with incoming waters, whereas Cd concentrations were similar for both waters. The suspended particulate matter was composed of a mixture of marine and continental material. The latter end-member was found to arise from the metal-rich ria bed sediments, which is diluted by the dominant metal-poor marine end-member. The net output flux of Cu from the channel is balanced by the freshwater inputs to the ria, and the net Zn flux gave a positive output to coastal waters. For Pb, the net flux to the coastal waters is less than that input from the rivers, as a result of its particle reactivity and deposition in sediments. On the contrary, a net input flux of dissolved Cd from coastal waters was observed, highlighting the oceanic source of this metal in the Galician rias. Results from the budget calculations are in agreement with the differential geochemical behavior of these elements in coastal waters.  相似文献   

17.
分别于2012年3月和7月对长江口及其邻近海域水体中溶解态铝的分布及其影响因素进行了研究,并在2012年3月至2013年11月期间对长江徐六泾进行了连续观测。结果表明,徐六泾溶解态铝在夏季出现最高值,在冬季呈现最低值,平均值分别为(313±130)nmol/L和(140±43)nmol/L,表现出与径流量相似的季节变化规律。受陆源输入变化的影响,长江口溶解态铝的浓度由近岸向外海逐渐降低,且呈现出明显的季节性差异,即7月明显高于3月。3月表、底层海水中溶解态铝的浓度范围分别为21~129 nmol/L和27~146 nmol/L,平均值分别为(49±21)nmol/L和(59±27)nmol/L;7月表、底层溶解态铝的浓度范围分别为6~332 nmol/L和9~252 nmol/L,平均值分别为(66±69)nmol/L和(83±74)nmol/L。在7月,表、底层溶解态铝呈现显著性差异,底层沉积物的再悬浮可能是造成差异的主要原因。调查结果表明,溶解态铝在长江口呈现出清除型行为,清除主要发生在咸淡水混合初期,初步计算出7月份溶解态铝的清除率约为55%。  相似文献   

18.
Geochemical and rock-magnetic investigations were carried out on a sediment core collected from the SE Arabian Sea at 1420 m depth in oxygenated waters below the present-day oxygen minimum zone. The top 250 cm of the core sediments represent the last 35 kaBP. The · 18O values of Globigerinoides ruber are heaviest during the Last Glacial Maximum (LGM) and appear unaffected by low-saline waters transported from the Bay of Bengal by the strong northeast monsoon and West Indian coastal current. The signatures of Bølling-Allerød and Younger Dryas events are distinct in the records of magnetic susceptibility, organic carbon (OC) and · 18O. Glacial sediments show higher OC, CaCO3, Ba, Mo, U and Cd, while the early-to-late Holocene sediments show increasing concentrations of OC, CaCO3, Ba, Cu, Ni and Zn and decreasing concentrations of Mo, U and Cd. Productivity induced low-oxygenated bottom waters and reducing sedimentary conditions during glaciation, and productivity and oxygenated bottom waters in the Holocene are responsible for their variation. The core exhibits different stages of diagenesis at different sediment intervals. The occurrence of fine-grained, low-coercivity, ferrimagnetic mineral during glacial periods is indicative of its formation in organic-rich, anoxic sediments, which may be analogous to the diagenetic magnetic enhancement known in sapropels of the Mediterranean Sea and Japan Sea. The glacial sediments exhibiting reductive diagenesis with anoxic sedimentary environment in this core correspond to reductive diagenesis and intermittent bioturbation (oxygenation) reported in another core in the vicinity. This suggests that the poorly oxygenated bottom water conditions during glacial times should not be generalized, but are influenced locally by productivity, sedimentation rates and sediment reworking.  相似文献   

19.
The concentrations of Si, Al, Ti, Fe, K, Ca, Mg, P and Mn, before and after chemical leaching, in particulate matter from waters off the west coast of Scotland have been measured in vertical profiles at two seasons. The distribution of Si and Ca are shown partly to reflect temporal changes in biological production in different waters. The distributions of Al, Ti, Fe, K and Mg have been used to distinguish different sources and types of suspended alumino-silicates, and to trace probable circulation patterns in the water mass.While Si and Ti contents of the particulate matter are unaffected by mild chemical leaching, large amounts of other elements, notably Mg, K and Al, can be removed by this treatment. Presumably, these losses indicate preferential release of these elements from octahedral and interlayer sites in clay mineral lattices.The distribution of particulate P covaries with non-silicate Fe in the surface waters, while in bottom waters, high concentrations of particulate Fe and Mn are associated. The relationship of Fe and P is considered to be due to the presence of particulate ferriphosphates derived from runoff. The particulate Mn and Fe in deep waters is produced by the precipitation of dissolved metals released from bottom sediments by diagenesis.  相似文献   

20.
通过对日本海Ulleung盆地KCES-1孔元素地球化学分析,探讨了过去48 ka以来日本海古生产力和古氧化还原环境的变化规律和影响因素。多种替代指标质量累积速率(总有机碳、CaCO3,磷、过剩钡、镉含量)显示日本海古生产力自48 ka以来发生了显著的变化。在48~18 ka低海平面和有限的水体交换导致表层水古生产力相对较低。在18~11 ka随着海平面的上升,富营养盐水团(亲潮和东海沿岸流水团)的流入导致古生产力逐渐增大,在12.6~11.5 ka古生产力达到最大值。在全新世对马暖流成为影响古生产力变化的重要因素,并且自5 ka以来古生产力保持相对稳定。古氧化还原替代指标(总有机碳、钼、铀、锰、碳与硫含量之比、自生铀、自生钼含量)显示在12~9 ka日本海底层水可能为无氧环境。古生产力高和底层水体有限的交换是诱发底层水缺氧的主要因素,而这又与全球气候变化和海平面变化有关。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号