48ka以来日本海Ulleung海盆南部的海洋沉积环境演化

晚第四纪以来伴随底层水含氧量的剧烈变化,浅色和深色沉积层的交替出现是日本海半远洋沉积物的主要特征。沉积特征分析表明,日本海Ulleung海盆南部KCES1孔的沉积物具有四种不同的沉积构造:均质、纹层、纹层状和混杂构造。深色沉积层一般具有纹层和纹层状构造,并且与我国内陆的千年尺度东亚夏季风强弱变化记录有很好的对应关系,表明纹层沉积物也具有千年尺度的变化规律,从而进一步说明了冰川性海平面变化和东亚夏季风波动应该是Ulleung海盆南部底层水溶解氧含量变化的主要原因。在暖期,在东亚夏季风降水相对增强的影响下,低温、低盐的东海沿岸水对日本海表层水体的贡献要大于对马暖流的贡献,日本海水体间的交换减弱,最终造成缺氧的海底沉积环境。在冷期,夏季风强度的减弱(冬季风增强)加快了日本海西北部深层水的生成,Ulleung海盆南部的底层水含氧量高,相应地沉积了具均质构造的浅色沉积物;在末次盛冰期最低海平面时,日本海成为一个封闭的海盆,降雨量高于蒸发量,水体出现分层,底层水处于停滞缺氧状态。自距今17.5 ka(日历年,下同)以来底层水含氧量较高,对马暖流逐渐成为影响日本海海洋沉积环境的主要因素。Ulleung海盆南部底层水的含氧量在YD期间有一定程度的降低,东海沿岸水的短暂强盛制约了深层水的流通。自距今10.5 ka以来对马暖流强盛,日本海海底处于富氧的沉积环境。     

Depositional environment in the southern Ulleung Basin, East Sea (Sea of Japan), during the last 48 000 years

The present study is based on the sedimentological data from a piston core KCES1 off the southern Ulleung Basin margin, the East Sea (Sea of Japan). The data include sediment color (L^*), X-ray radiographs, grain size distribution and AMS¹⁴C date. Four kinds of sediments (homogeneous, laminated, crudely laminated and hybrid sediments) are identified according to the characters of the sedimentary structures that were considered to reflect changes in bottom-water oxygenation. Alternations of dark laminated/crudely laminated sediments and light homogeneous sediments represent millennial-scale variations that are possibly associated with the high-resolution changes in the East Asian monsoon (EAM). The relative contributions of the East China Sea Coastal Water (ECSCW) and the Tsushima Warm Current (TWC) were likely the main reasons for the repetition of the anoxic and oxic depositional conditions in the East Sea since the last 48 ka BP. During the interstadial, the strengthen summer EAM was attributed to the expansion of the ECSCW because of more humid climate in central Asia, and then more strongly low-salinity, nutrient-enriched water was introduced into the East Sea. The ventilation of deep water was restricted and therefore the dark laminated layer deposited under the anoxic bottom water condition. During the lowest stand of sea level in the last glacial maximum (LGM), the isolated East Sea dominated by stratiˉed water masses and the euxinic depositional environment formed. The homogenous sediments have been predominating since 17.5 ka BP indicating that the TWC has intruded into the East Sea gradually with the stepwise rise of sea level and the bottom water oxygen level was high. During the late Younger Dryas (YD) period, the last dark laminated layer deposited because the ventilation of bottom water was restricted by stronger summer EAM. The TWC strengthened and the bottom water became oxic again from 10.5 ka BP.     

Sedimentation in a tropical fjord: Golfo Dulce, Costa Rica

Sedimentation processes in Golfo Dulce, a periodically anoxic fjord-like embayment on the Pacific coast of Costa Rica, have been investigated by analyses of surface sediments and 3.5-m-long sediment cores. The large proportion of non-biogenic material (>90%) reflects the dominance of terrigenous sediment input to Golfo Dulce. Biogenic components such as organic carbon and carbonate are also supplied from terrigenous sources. The two components, however, originate from different parts of the coast surrounding the gulf. The sediment cores did not show any laminated sections. The sediments can be divided into turbiditic basin deposits and almost undisturbed, hemipelagic slope deposits.     

Late Quaternary chronology of the southern Black Sea basin

During New Euxinian time when sea level dropped below the sill connecting the Black and Marmara seas, the Black Sea became isolated and freshwater sediments were deposited. Now it is a semieuxinic basin with the oxic/anoxic boundary at 100–150 m. The seasonal changes in sedimentation are preserved in the form of laminated sequences. The counting of varves in southeastern Black Sea cores show the chronology of the O₂/H₂S interface. The age of the Holocene sapropel along the eastern margin ranges from 4000 to 1000 yr BP in deep water and 2500—1000 yr BP in shallower water. Sapropel formation started at 3650 yr BP at a water depth of 2200 m.     

Origin and differentiation of clay minerals in pelagic sediments and sapropels of the Bannock Basin (Eastern Mediterranean)

Two cores from an anoxic basin of the southeastern Mediterranean Ridge were investigated to compare the clay mineralogy of pelagic sediments and of the interbedded sapropels. The sediments of Core BAN 84-02, raised from the basin floor, and those of Core BAN 84-08, from the eastern plateau of the Bannock Basin, provide evidence for different sedimentary environments. The anoxic conditions, which are still present near the bottom, produce an important decrease in smectite crystallinity (Core 02), whereas well-organized smectite persists in the normally oxygenated sediments (Core 08). Detrital clay minerals from various sources were deposited in the basin and no appreciable diagenesis was recognized downcore.

The clay mineralogy of the sapropels shows remarkable differences compared to the pelagic sediments. The changes observed are dependent on aggressive chemical reaction and on the sudden input of detrital crystalline sediments into the stagnant environment. A climatic curve registers the variable degree of clay mineral hydrolysis in continental areas and exhibits good correspondence with an already published oxygen isotope curve for the area.     

The nature,distribution and origin of a sapropelic layer in sediments of the Silicia Basin,northeastern Mediterranean

A sapropelic layer with organic carbon contents of 1.0–1.5%, in contrast to the usual 0.2–0.5% of adjacent normal basin sediments, is found to be widespread in sediment cores collected from the Cilicia Basin, northeastern Mediterranean. The horizon is thought to be equivalent to the S₁ sapropel of other workers. It is finely laminated with no evidence of bioturbation, has a very markedly low magnetic susceptibility, and contains a significantly higher content of pollen and plant debris than is found in the normal basin sediment. The stable oxygen and carbon isotope values suggest that the layer formed during post-glacial climatic warming when fresh nutrient-rich surface water flowed into the Cilicia Basin from the surrounding land to produce a stratified water mass which allowed the development of anoxic bottom waters. The distribution of the sapropelic layer indicates that anoxic conditions extended to within approximately 350 m of sea level during deposition, a depth shallower than previously recorded in the Eastern Mediterranean.     

Interstitial water trace-metal chemistry of laminated sediments from the Gulf of California,Mexico

This report presents major and minor element profiles for interstitial waters recovered from the oxygen-minimum zone of the Gulf of California. The major elements and nutrients show concentration-depth profiles typical for anoxic, laminated sediments, with sulfate-reduction occurring close to the sediment-water interface, accompanied by increases in alkalinity and ammonia. Barium is solubilized near the sediment-water interface, but decreases below 10 cm depth, showing concentrations consistent with barite solubility. The dissolved concentrations of Mn, Fe, and Al are higher in the upper part of the sedimentary column; Mn and Fe due to reduction of oxides and Al probably because of dissolution of siliceous material. In contrast, dissolved Mo, V, and Cr show concentrations increasing with depth. The strong correlation of the concentrations of Mo, V and Cr with “yellow substance” absorbance reflect the importance of dissolved organic matter for the mobility of these elements during early diagenesis.     

Evaluation of extraction schemes for organic matter in anoxic estuarine sediments

A persistent criticism of studies of organic matter in sediments and soils has been that the extracted products used in these investigations may not resemble the original material, particularly if harsh extractants such as NaOH, Na₄P₂O₇ or HCl are employed. To minimize chemical changes, a mild separation procedure has been developed for obtaining soluble organic matter from anoxic estuarine sediments. The resulting complex mixture of organic compounds can be analyzed by reversed-phase liquid and size-exclusion chromatographic methods, which monitor the relative molecular polarity and size, respectively. The effects of the strong reagents NaOH, Na₄P₂O₇ and HCl, as well as exposure to the atmosphere and bacterial activity on this anoxic sedimentary extract has been investigated. In each instance, significant degradation of anoxic organic matter occurs, producing molecules of increased polarity and reduced molecular weight. These data indicate that extreme care is necessary to avoid artifacts in preparation and handling of samples.     

A simple guideline to apply excitation-emission matrix spectroscopy (EEMs) for the characterization of dissolved organic matter (DOM) in anoxic marine sediments

Marine sediments represent a major carbon reservoir on Earth. Dissolved organic matter(DOM) in pore waters accumulates products and intermediates of carbon cycling in sediments. The application of excitation-emission matrix spectroscopy(EEMs) in the analysis of subseafloor DOM samples is largely unexplored due to the redoxsensitive matrix of anoxic pore water. Therefore, this study aims to investigate the interference caused by the matrix on EEMs and propose a guideline to prepare pore water sam...     

Carbonaceous metalliferous sediments and oceanic anoxic events in the Earth’s Phanerozoic history

The oceanic anoxic events (OAE) intermittently occurring in the Earth’s Phanerozoic history left fingerprints in the geological record in the form of carbonaceous metalliferous sediments. The analysis of the available data on the S, Mo, Sr, Os, and Nd isotope compositions reveals that the role the volcanic factor was multiply higher during the accumulation of these sediments. The sediments maximally enriched in planktonogenic organic matter (up to 5% on average and up to 30% in separate layers) are widespread on continental margins and in adjacent onshore areas. On active margins, they are largely confined to the back parts of marginal seas, where they are characterized by lower organic matter concentrations (averaging approximately 2.5% and up to 10% in separated beds). The deposition of carbonaceous metalliferous sediments in the Phanerozoic associates with 16 oceanic anoxic events, which happened in different geodynamic settings with intensified ophiolitic, island-arc, and trappe volcanism. The underwater lava eruptions and hydrothermal solution discharges served as a triggering mechanism for the chemical, biological, sedimentological, and climatic processes that stimulated the development of anoxic environments in the ocean and the deposition of carbonaceous metalliferous sediments.     

Analysis of the Black Sea sediments by evaluating DSDP Leg 42B drilling data for gas hydrate potential

Many gas seepages, temperature, pressure, salinity, anoxic environment and high source gas potential of the Black Sea indicates that the Black Sea might have huge potentials for biogenic and thermogenic gas hydrates. However, the last important parameter to consider gas hydrate as an energy source is the type of sediments. Coarse marine sands are considered as good hydrate reservoirs because of high porosity and high permeability. Only very limited data is available related to the types of lithology of the Black Sea sediments. Hence, in this study, the literature data (especially the drilling and coring data of DSDP Leg 42B program) about gas seepages, temperature gradient, pressure gradient, salinity, anoxic environment and high source gas potential, and the types of the sediments in the Black Sea were investigated and analyzed. Although gas seepages, temperature gradient, pressure gradient, salinity, anoxic environment and high source gas potential of the Black Sea are appropriate for producible gas hydrate reservoirs, the sediments of the Black Sea appear to be generally fine grained with high clay content. Sandy-silt and silty sand layers in turbidites of the Black Sea might be potential producible hydrate reservoirs but these sediments are fine. As well as turbidites, separate thin sand layers might be potential gas hydrate reservoirs as an energy source in the Black Sea.     

Yangtze offshore,China: highly laminated sediments from the transition zone between subaqueous delta and the continental shelf

This study examines the deposition of highly laminated muddy sediment in vibrocores recovered from a depth of 40–55 m of water and located 120 km east of the Yangtze River mouth. X-radiographs show numerous sharp-based sedimentary rhythmics with nearly parallel and undulated laminations, interbedded with silty lenses and interbeds. The laminated sediment varies from clayey silt to silty clay. AMS radiocarbon dates on well-preserved bivalves are primarily younger than 5500 y BP, indicating the formation of the laminated sediment under the present sea-level conditions. Macro- and microfossils in the sediments are consistent with the modern offshore sedimentary setting. The laminated sediment originated from the Yangtze estuary, but the sedimentation processes were not deltaic. The highly laminated sediment that lies below the normal wave base of 10 m was deposited on the seaward margin of the Yangtze subaqueous delta, closely associated with submarine tidal and storm-generated currents.     

The influence of sediment resuspension on the degradation of phenanthrene in flow-through microcosms

The effect of sediment resuspension on the mineralization of phenanthrene was examined in microcosms and sediment slurries. In computer-controlled, flow-through microcosms, 14C-phenanthrene-amended sediments were resuspended into overlying oxic water at frequencies of 12, 4, 1, 0.25 and 0 d(-1). In slurry bottle experiments 14C-phenanthrene-amended sediments were continuously resuspended under oxic (excess air headspace) and anoxic (N2 headspace) conditions and mineralization was measured at periods from 2 h to 7 days. Our main findings were: (1) mineralization rate constants from the microcosms ranged from 0.001 to 0.01 d(-1) and increased with frequency of resuspension, (2) these rates fell between those measured in oxic and anoxic slurries and were predicted within a factor of 2.5 by a model in which mineralization depended on the degree of oxygen exposure, and (3) the phenanthrene-degrading bacterial community was more active in resuspended sediments incubated in the microcosms than in sediments which were not resuspended, or which were stored under refrigeration. We conclude from these experiments that the effects of sediment resuspension on phenanthrene degradation are consistent with a primary role of average oxygen exposure, and also an alteration in the PAH-degrading activity of microbial populations.     

Effects of fine grain size on distribution of Mn in shallow and deep water Black Sea sediments: A comparison between oxic and anoxic depositional environments

The uppermost 5–6 cm of the sediments (between 8 and 2248 m water depths) were studied to understand the effects of varying redox conditions on the Mn distribution in the recent sediments of the Black Sea. It was found that most Mn concentrations are consistent with the average abundance in crustal and/or sedimentary rocks. There exist no important differences between Mn concentrations in oxic (shallower water; <70 m) and anoxic (deeper water; 120 m) sediments. Previously reported Mn-enrichment above the Black Sea oxic/anoxic interface, due to the peculiar redox cycling, shows no significant contribution of Mn to the bottom sediments. A marked relationship between total Mn concentrations and clay/mud contents at shelf depth along the southern Black Sea margin indicates increased accumulation of Mn in association with the fine-grained particles and eastward water circulation.     

Effect of sample pretreatment on the reliability of solid speciation data of heavy metals — implications sesfor the study of early diagenetic processes

Experimental data on anoxic freshwater sediments from the Hamburg harbor indicate that commonly performed storage and pretreatment methods including aeration by drying strongly change the original associations of heavy metals with different sediment components. Oven-drying as well as freeze-drying under ‘vacuum’ affects metals originally bound to carbonate (Fe, Mn) and to the sulfidic/organic fraction (Zn, Cd, Cu, Pb), as indicated by sequential chemical extractions. While the easily oxidizable Cu and Pb portions are transferred mainly into the moderately reducible fraction, those of Zn and especially Cd are found in easily reducible and labile exchangeable fractions upon aeration of the sediment. Metals from only the latter fractions are potentially mobilizable via pore-water fluxes. Useful information on solid speciation influencing the mobility of contaminants in biogeochemically reactive sediments by the chemical leaching approach requires, therefore, proper and careful handling of the anoxic sediment samples.     

Sedimentologic,mineralogic, and geotechnical descriptions of fine-grained slope and basin deposits,Baffin Island Fiords

Sediments from Baffin Island fiords are graded, massive, laminated, or bioturbated. Plasticity indices vary with sediment type (lowest = laminated or graded; intermediate = massive; and highest = bioturbated). Graded and massive silty/sandy muds are most common on prodelta or proglacial slopes. Bioturbated graded and laminated muds, and rare massive pebbly muds occur more distally down-fiord from the deltas or glaciers. Clays are mostly mica, with only minor to moderate amounts of chlorite, kaolinite, and swelling clays. On the Casagrande plasticity chart, the sediments plot in fields for clay-size material of medium to high plasticity.     

The effect of manganese oxide scavenging on molybdenum in saanich inlet,British Columbia

A simple colorimetric method was developed for determining molybdenum in seawater by solvent extraction of its dithiolate and was then applied during a nine month study of Saanich Inlet. This inlet is a fjord on the coast of Vancouver Island, British Columbia, in which the bottom waters alternate between a weakly oxygenated and anoxic state. Results are given for the concentrations of dissolved and suspended molybdenum, suspended manganese, dissolved oxygen and of salinity measurements. Salinity-molybdenum correlations demonstrate that the deep waters are deficient in molybdenum, a conclusion consistent with reports that the sediments deposited in the reducing zone are enriched with molybdenum precipitated from the anoxic bottom waters. Suspended manganese, which occurs in large amounts as a result of the oxidative precipitation of dissolved Mn(II) diffusing from anoxic waters, has a distribution that is directly correlated to that of suspended molybdenum and which tends to be inversely related to that of dissolved molybdenum, suggesting that molybdenum is being coprecipitated with manganese oxides. Such a hypothesis is supported by the fact that the average molybdenum to manganese weight ratio of suspended matter closely approximates that of local manganese nodules, and by a mathematical analysis of the distribution data which includes development of a model for scavenging. Computations using the model relationships indicate that manganese oxide scavenging tends to concentrate molybdenum in the reducing waters where the anoxic processes responsible for its deposition in the sediments become operative. Additional calculations based upon current estimates of oceanic residence times suggest that manganese-oxide scavenging operating on an oceanic scale could be removing approximately 10% of the molybdenum being added to the oceans.     

The fate of heavy metals in an estuarine tropical system

The scope of this work is the study of the distribution and accumulation of Cu, Cr, Cd, Pb and Hg in waters and sediments from Guanabara Bay, Rio de Janeiro. An attempt was made to balance removal to the sediments and outputs from the bay. Metal contamination in the sediments is only observed at short distances from the identified point sources. In spite of high primary productivity, the sediments are relatively poor in organic carbon content due to intensive respiratory processes already occurring in the water column. This, together with a very efficient tidal current system which brings oxygen-rich waters in contact with anoxic sediments, certainly plays an important role in heavy metal remobilization.     

The partitioning of organic carbon fluxes and sedimentary organic matter decomposition rates in the ocean

The partitioning of annual organic carbon fluxes from five stations located in the vicinity of the Pacific-Antarctic Ridge and the Peru continental margin suggests that 35–85% of the total near-bottom organic carbon flux is utilized at or near the sediment-water interface. These estimates have large uncertainties, but illustrate that assessments of organic carbon utilization can be made by several stepwise approaches which are generally applicable to a wide spectrum of marine environments.In one approach, the mineralization of organic carbon from the sediments was predicted from both sedimentary organic carbon and pore water nutrient profiles with comparable results. Neglecting sediment mixing, the rate constants of the anoxic sediments off Peru range from 0.1 × 10^?3 to 4 × 10^?3 y^?1, and rate constants derived for oxic SW Pacific sediments range from 3 × 10^?4 to 7 × 10^?4 y^?1. As with other values reported for sulfate reducing sediments by Toth and Lerman (1977) and for oxic central Pacific sediments by Müller and Mangini (1980), log-log plots of rate constants vs. sedimentation rate define two parallel linear relationships for oxic and anoxic sediments, respectively. The apparently enhanced rates for oxic environments may result from large benthic organisms which redistribute a portion of the available detritus and in doing so convert it into more easily accessible and metabolizable organic matter. In low-oxygen environments, bottom feeders and infauna are less abundant and more likely to irrigate rapidly accumulating sediments.     

末次盛冰期以来冲绳海槽中部沉积物有机碳和磷的地球化学研究

利用元素及同位素地球化学方法研究了冲绳海槽中部沉积物岩芯中有机碳及磷的地球化学特征及影响因素。结果表明,冲绳海槽沉积速率（16.5~32.5 cm/ka）变化小,不是沉积物中有机碳埋藏的重要影响因素。相对于全新世氧化性底水环境,末次盛冰期/冰消期冲绳海槽缺氧底水环境提高了沉积物对有机碳的埋藏效率。冲绳海槽沉积物中各形态磷的相对含量与其他边缘海沉积物中的相似。交换态磷（Ex-P）含量低、变化小。末次盛冰期/冰消期缺氧底水环境下铁氧化物的还原溶解导致铁结合磷（Fe-P）释放以及自生磷矿物（Au-P）的形成。全新世氧化性底水条件有利于铁氧化物的有效再生及对磷的再吸附,但不利于Au-P的保存。总有机碳（TOC）和有机磷（Org-P）之间良好的相关性表明TOC埋藏对Org-P含量的重要控制作用。冲绳海槽沉积物中碎屑磷（De-P）含量低于长江口及东海陆架沉积物中的含量,这与陆源碎屑向外海传输减弱有关。在约9.3 ka BP（岩芯200 cm深度）,TOC、Fe-P、Org-P、De-P以及Fe_HR均出现的极小值可能由物质坡移造成。