Oceanographic controls on the carbon isotopic compositions of sinking particles from the Cariaco Basin

This study examined the relationship between carbon isotopic composition of sinking organic matter (OM) and the biological, physical and chemical properties of the surface ocean in the Cariaco Basin. The ¹³C/¹²C ratio of OM (δ¹³C_org) in sinking particles was determined on sediment trap samples from four depths collected from 1996 to 1999 as part of the CArbon Retention In A Colored Ocean time series. Water column properties, including temperature, productivity, chlorophyll and concentration of dissolved CO₂, were concurrently measured on monthly cruises. The δ¹³C_org varied from a high of –17.7‰ to a low of –22.6‰ during the study period. The variation of the δ¹³C_org throughout seasonal cycles was directly proportional to the strength of upwelling and was negatively correlated with temperature (r²=0.64). During the 1996–1997 upwelling event, the strongest during the study period, the δ¹³C_org increased by 4.4‰ whereas during the 1998–1999 upwelling event, the weakest during the study period, the δ¹³C_org only increased by 3.3‰. Contrary to most previous studies, we observed a negative relationship (r²=0.53) between [CO_2 aq] and the estimated isotopic fractionation factor (ε_p). However, there was no correlation between ε_p and the calculated growth rates indicating that there was non-diffusive uptake of carbon into phytoplankton cells. It thus appears that [CO_2 aq] does not control the δ¹³C_org in the water column of the study site. The best explanation for the isotopic enrichment observed is a carbon concentrating mechanism (CCM) in phytoplankton. The existence of a CCM in phytoplankton has major implications for the interpretation of the δ¹³C_org in the Cariaco Basin.     

Hydrolytic ectoenzyme activity associated with suspended and sinking organic particles within the anoxic Cariaco Basin

Ectohydrolase activities of suspended microbiota were compared to those associated with sinking particles (sed-POM) retrieved from sediment traps deployed in the permanently anoxic Cariaco Basin. In shore-based assays, activities of aminopeptidase, β-glucosidase, chitinase and alkaline phosphatase were measured in samples obtained from oxic and anoxic depths using MUF- and MCA-labeled fluorogenic substrate analogs. Hydrolysis potentials for these enzymes in the seston varied widely over the nine cruises sampled (8 Nov 1996–3 May 2000) and among depths (15–1265 m); from <10 to over 1600 nM d^?1 hydrolysate released, generally co-varying with one another and with suspended particulate organic carbon (POC) and particulate nitrogen (PN). Hydrolytic potentials, prokaryotic abundances and POC/PN concentrations in sinking debris were 400–1.3×10⁷ times higher than in comparable volumes of seawater. However when normalized to PN, hydrolytic potentials in sediment trap samples were not demonstrably higher than in Niskin bottle samples. We estimate that PN pools in sediment trap samples were turned over 2–1400 times (medians=7–26x) slower by hydrolysis than were suspended PN pools. Median prokaryotic growth rates (divisions d^?1) in sinking debris were also ～150 times slower than for bacterioplankton. Hydrolytic potentials in surface oxic waters were generally faster than in underlying anoxic waters on a volumetric basis (nM hydrolysate d^?1), but were not significantly (p>0.05) different when normalized to PN or prokaryote abundances. Alkaline phosphatase was consistently the most active ectohydrolase in both sample types, suggesting that Cariaco Basin assemblages were adapted to decomposing phosphate esters in organic polymers. However, phosphorus limitation was not evident from nutrient inventories in the water column. Results support the hypothesis that efficiencies of polymer hydrolysis in anoxic waters are not inherently lower than in oxic waters.     

Oceanographic and climatologic controls on the compositions and fluxes of biogenic materials in the water column and sediments of the Cariaco Basin over the Late Holocene

Materials collected by sediment traps over a 3-y period and sedimentary horizons from a gravity core covering the last 6000 y were used to investigate the effects of climate-related processes such as wind-driven upwelling and regional rainfall on the production, export and burial of particulate organic matter in the Cariaco Basin. A variety of chemical analyses, including organic carbon and nitrogen, biogenic opal, calcite, lithogenic contents, stable carbon isotopic ratios of organic matter and the yields of CuO reaction products derived from distinct biochemicals such as amino acids, fatty acids and lignins, were carried out for this purpose. Principal component analyses were used to investigate the trends in this multivariate data set. These analyses reveal marked temporal differences in the composition of the materials sinking through the water column, which were related to distinct oceanographic and climatic forcings. For example, autochthonous fluxes, characterized by elevated contents of organic carbon and opal as well as high yields of amino acid and fatty acid reaction products, displayed peaks during periods of intense wind-driven upwelling. In contrast, allochthonous materials, characterized by elevated lithogenic contents and elevated yields of lignin-derived products, were more important during periods of high rainfall, low wind and enhanced stratification. In addition to the strong seasonal contrasts, there was significant temporal variability at both shorter (monthly) and longer (inter-annual) time scales. Hence, other factors, such as zooplankton grazing and El Niño effects on local climatology, may also be important. Examination of the gravity core record yielded several significant trends. For example, there was a marked increase in sediment accumulation rates from 5000 to ca. 700 y before present with concomitant increases in the concentrations of organic carbon, opal and most biomarkers. These results suggest that the Cariaco Basin experienced a marked increase in primary productivity and particle flux to the underlying sediments since the Holocene Thermal Maximum. Also within the sedimentary record, we observed distinct variations in the relative contributions of autochthonous and allochthonous organic matter. The frequency of these variations is roughly 1500 y and appears to match ice-rafted debris records from the North Atlantic. Such coincidence indicates cold periods within the Holocene, which are related to minima in insolation, may have led to the southern migration of the inter-tropical convergence zone and the enhancement of wind-driven upwelling, primary productivity and autochthonous organic matter flux to the seabed in the Cariaco Basin. Alternatively, during warm periods, the opposite climatic conditions would have increased both the thermal stratification of the water column and average rainfall in the Cariaco Basin, leading to elevated inputs of allochthonous materials.     

Seasonal and vertical variations of sinking particle fluxes in the West Caroline Basin

A sediment trap experiment was carried out in the West Caroline Basin, located in the equatorial western Pacific between influences of the Asian monsoon and the open ocean. Annual mass flux at the shallow trap at Site 1 was 57.10 g m^-2 yr^-1. Generally, the higher flux of organic matter was associated with higher activities of biogenic opal-producing and carbonate-producing plankton communities. In addition, as the organic matter content increases, the organic carbon/carbonate carbon ratio shows a tendency to increase. Carbonate-producing plankton was predominant during periods 1 and 3 (May to July and November to the beginning of December), which could be due to limited silica supply to the euphotic zone. On the other hand, surface sea water was more nutrient-rich during periods 2 and 4 (August to October and the end of December to April) at Site 1. These high total mass fluxes could be stimulated by wind.The amount of biogenic components collected in the sediment traps and the accumulation in surface sediments at Site 1 could be compared with primary productivity values. Carbonate and biogenic opal fluxes were 99% and 90% less, respectively, in the surface sediments compared to those in the shallow sediment trap. This could be due to the reaction of sinking particles with undersaturated deep sea water just above the sea floor, rather than with the water column during sinking. About 20% of the organic matter was decomposed between the shallow and deep sediment traps and more than 98% between the deep sediment trap and final burial in the surface sediments. The relative amount of organic carbon preserved in surface sediments was about 0.10% of annual primary productivity.     

The importance of subsurface nepheloid layers in transport and delivery of sediments to the eastern Cariaco Basin,Venezuela

Optical transmissometer measurements were coupled with particulate organic matter (POM) observations to understand suspended sediment composition and distribution in the eastern Cariaco Basin during the rainy seasons of September 2003 and 2006. Our results suggest that nepheloid layers originating at the mouth of small mountainous rivers discharging into the eastern Basin are a major delivery mechanism of terrigenous sediments to the Basin interior. Intermediate nepheloid layers (INL) were observed near the shelf break (～100 m) and appear to effectively transport terrigenous material laterally from the shelf to deep waters, thereby providing a plausible supply mechanism of the terrestrial material observed in sediment traps. These findings highlight the importance of small, local rivers in the Cariaco Basin as sources of terrestrial material. In contrast, these nepheloid layers contained only limited POM. When this information is combined with published sediment trap POM data, it suggests that nepheloid layers may not be a primary mechanism for delivering terrigenous POM to the deeper waters of the basin during the rainy season. Rather, BNL may redistribute marine-derived POM from shallow waters to the Basin's interior by providing ballast materials, particularly during episodic events driven by wind and precipitation. Though we have determined that nepheloid layers play an important role in the seaward transport of particulate material in the Cariaco Basin, their composition and temporal variability have not been fully characterized. This is critical to understand lateral particle transport, since nepheloid layers constitute a significant source of sediment to the deep Cariaco Basin.     

Seasonal and interannual dynamics in diatom production in the Cariaco Basin,Venezuela

We examine the diatom flux collected between November 1996 and April 1998, and between January and October 1999 at the time-series study site in the Cariaco Basin, off Venezuela. The temporal dynamics of the total diatom flux mainly reflect seasonal, trade wind-driven changes in surface hydrographic conditions, including changes associated with the El Niño/Southern Oscillation (ENSO). Highest diatom fluxes (>1.8×10⁷ valves m^?2 d^?1) coincided with the upwelling season in boreal winters 1997 and 1999. Changes in the composition of the diverse diatom community reflect variations in hydrographic and atmospheric conditions, as well as nutrient availability. Cyclotella litoralis, a neritic diatom typical of nutrient-rich waters, along with resting spores of several Chaetoceros spp., dominate during periods of high diatom flux, following trade wind-driven upwelling. During the boreal summers of 1997 and 1999, nutrient-depleted surface waters resulted in low diatom fluxes (<5.2×10⁶ valves m^?2 d^?1). The seasonal pattern of high diatom production was altered from July 1997 through April 1998, when the ENSO affected the Caribbean Sea. The occurrence of ENSO during boreal winter 1997–1998 caused a major change in the qualitative composition of the diatom assemblage: the highly diverse diatom assemblage was composed of a mixture of pelagic (Nitzschia bicapitata, Thalassionema nitzschioides var. inflata, T. nitzschioides var. parva, Azpeitia tabularis) and coastal species (C. litoralis, resting spores of Chaetoceros, T. nitzschioides var. nitzschioides). The simultaneous occurrence of neritic and open-ocean diatoms during boreal summers reflects the fact that the Cariaco Basin is influenced by both offshore and coastal waters, with considerable short-term variability in hydrographic conditions and nutrient availability.     

Controls on temporal variability of the geochemistry of the deep Cariaco Basin

Studies of the Cariaco Basin on the continental shelf of Venezuela, as a part of the Carbon Retention In A Colored Ocean (CARIACO) program, have revealed that the chemistry of the deeper waters of the system is more variable than previously believed. Small oxygen maxima have been observed on a number of occasions at depths where oxygen was previously absent, suggesting the occurrence of intrusions of oxygenated water into the region of the oxic/anoxic interface (250–300 m). Apparently because of these events, the oxic/anoxic interface deepened by about 100 m during the period of our observations. We also observed a dramatic decrease in H₂S concentrations at all depths below the oxic/anoxic interface during this same period. Bottom waters, for example, had an H₂S concentration of about 75 μM in November 1995, but since November 1997, concentrations in bottom water have not exceeded 55 μM. Water of sufficient density to sink to the bottom of the Basin has been observed on one occasion at sill depth just north of the eastern sill. However, based on a simple box model, the decrease in deep-water sulfide does not appear to be due to intrusion of oxygenated water alone, as concentrations of other measured species, and of hydrographic parameters, have remained constant with time. Instead, we postulate that an earthquake that took place in July 1997 resulted in a turbidity current that transported large quantities of coastal sediment containing oxidized iron into the deep waters of the basin. If the final products of reaction were elemental sulfur and iron sulfide, the sediment associated with the oxidized iron would have produced a turbidite layer about 10 cm thick. Previous earthquakes have produced turbidites of similar thickness.     

Biogenic components and elements in sediments of the Central Baltic and their redistribution

The content and distribution of biogenic components (CaCO₃ and SiO_2am) and elements (C_org, N and P) and some metals (Fe and Mn) were investigated in the marine Holocene sediments of the Baltic Sea including the Curonian and Vistula Lagoons and the Gulf of Riga. The average contents of the studied components and elements are increasing in the order: sand–coarse silt–fine silty mud–mud–pelitic (clayey) mud. The sand and the pelitic mud contain in average (in %): CaCO₃ 1.30 and 8.46; C_org 0.38 and 3.27; SiO_2am 1.32 and 3.11; P 0.05 and 0.10; Fe 1.49 and 4.67; Mn 0.03 and 0.04, respectively. Maps of the areal distributions were compiled and show that areas of elevated values are located mainly in the central parts of lagoons or deep areas. Based on the sediment thickness it is proposed that strong near-bottom currents beneath the halocline level exist in the Eastern-Gotland Deep. The thin mud layer (or the absence of mud) and low sedimentation rates may suggest that non-deposition and resuspension of bulk sediments and associated nutrients occur in many peripheral and central parts of the Eastern-Gotland Deep at depths of more than 90–220 m.     

南海东北部和南部海域表层沉积物生物硅研究

本研究测定了南海东北部和南部海域表层沉积物的生物硅含量(SiO2%),其含量范围分别为1.08%-3.01%和0.79%-9.06%,平均值分别为1.76%和4.22%.研究结果表明,南海表层沉积物中的生物硅含量与站位水深呈正相关关系;南海东北部的表层沉积物中的生物硅含量与其中的矿物含量、铁离子浓度、间隙水中的营养盐浓度不存在明显的相关性;南海南部海域表层沉积物中的生物硅含量与烧失量、有机碳含量、碳酸盐含量呈正相关关系,与粘土矿物含量相关性不明显.     

大亚湾西部海域沉积物中生物硅的含量及其分布特征

采用2. 0 mol/dm~3Na_2CO_3溶液5h单点化学提取-硅钼蓝连续分光光度分析法分别测定了大亚湾西部海域13个表层沉积物和1个沉积物岩芯中生物硅的含量.表层沉积物和沉积物岩芯中生物硅含量占比分别为0. 69%～2. 02%和1. 24%～2. 05%,平均值分别为1. 42%和1. 60%.结果证实西大亚湾沉积物中生物硅含量水平与我国南海近岸海域基本一致.在210Pbex测年的基础上,通过分析沉积物岩芯中生物硅、有机物、无机碳等多指标,揭示近百年来大亚湾周边环境变化对海洋环境的影响,证实了上世纪80年代以来西大亚湾周边农业、海水养殖业和工业发展等人类活动加剧了该海域生态环境变化,尤其90年代核电站运行对海洋生态变化造成一定的影响.     

南大洋普里兹湾沉积物中生物硅含量与分布

利用中国第18,21次南极考察获得的沉积物样品,对南大洋普里兹湾沉积物中生物硅(BSiO₂)的含量以及分布特征进行了初步研究.结果表明:普里兹湾表层沉积物中生物硅含量丰富,生物硅含量在4.89%~85.41%之间变化,平均为30.90%.最高值出现在湾内的IV-10站.生物硅的垂向分布与间隙水中硅酸盐呈现相反的变化趋势.表层沉积物中生物硅和有机碳分布趋势与表层海水中叶绿素a、初级生产力的分布趋势密切相关,最大值均出现在普里兹湾环流中心区域,较好地反映了上层水体中初级生产力的变化状况.     

Benthic trophic status and nutrient fluxes in shallow-water sediments

Proliferation of fast-growing ephemeral macroalgae in shallow-water embayments constitutes a large-scale environmental change of coastal marine ecosystems. Since inorganic nutrients essential for the initiation and maintenance of macroalgal growth may be supplied from the underlying sediment, we investigated the coupling between benthic inorganic nutrient (mainly N and P) fluxes and sediment properties in 6 bays representing a wide gradient of sediment characteristics (grain size, organic matter content, solid phase C and N). The initial characterization of bays was made in June and also included measurements of oxygen flux and microphytobenthic and macrofaunal biomass. In September, still within the growth season of the macroalgae, complementary experiments with sediment-water incubations for benthic flux measurements of oxygen and nutrients focused on trophic status (balance between auto- and heterotrophy) as a controlling factor for rates of measured benthic nutrient fluxes. Generally, sediments rendered autotrophic by microphytobenthic photosynthesis removed nutrients from the overlying water, while heterotrophic sediments supplied nutrients to the overlying bottom water. Estimations of the green-algal nutrient demand suggested that late in the growth season, net heterotrophic sediments could cover 20% of the N-demand and 70% of the P demand. As the benthic trophic status is a functional variable more closely coupled to nutrient fluxes than the comparably conservative structural parameter organic matter content, we suggest that the trophic status is a more viable parameter to classify sediments and predict benthic nutrient fluxes in shallow-water environments.     

Oxygen and organic carbon fluxes in sediments of the Bay of Biscay

The relationship between particulate organic carbon (POC) concentrations measured in modern sediment and fluxes of exported POC to the sediment surface needs to be understood in order to use POC content as a proxy of paleo-environmental conditions. The objective of our study was to compare POC concentrations, POC mineralization rates calculated from O₂ consumption and POC burial rates. Benthic O₂ distributions were determined in 58 fine-grained sediment cores collected at different periods at 14 stations in the southeastern part of the Bay of Biscay with depths ranging from 140 to 2800 m. Depth-dependent volume-specific oxygen consumption rates were used to assess rates of aerobic oxidation of organic matter (OM), assuming that O₂ consumption solely was related to heterotrophic activity at the sediment–water interface. Heterogeneity of benthic O₂ fluxes denoted changes in time and space of fresh organic material sedimentation. The most labile fraction of exported POC engendered a steep decrease in concentration in the upper 5 mm of vertical O₂ profiles. The rupture in the gradient of O₂ microprofile may be related to the bioturbation-induced mixing depth of fast-decaying carbon. Average diffusive O₂ fluxes showed that this fast-decaying OM flux was much higher than buried POC, although diffusive O₂ fluxes underestimated the total sediment oxygen demand, and thus the fast-decaying OM flux to the sediment surface. Sedimentary POC burial was calculated from sediment mass accumulation rate and the organic carbon content measured at the top of the sediment. The proportion of buried POC relative to total exported POC ranged at the most between 50% and 10%, depending on station location. Therefore, for a narrow geographic area like the Bay of Biscay, burial efficiency of POC was variable. A fraction of buried POC consisted of slow-decaying OM that was mineralized within the upper decimetres of sediment through oxic and anoxic processes. This fraction was deduced from the decrease with depth in POC concentration. At sites located below 500 m water depth, where the fast-decaying carbon did not reach the anoxic sediment, the slow-decaying pool may control the O₂ penetration depth. Only refractory organic material was fossilized in sedimentary records at locations where labile OM did not reach the anoxic portion of the sediment.     

楚科奇海表层沉积物的生源组分及其对碳埋藏的指示意义

工业革命以来大气中CO₂浓度由280 ppm剧增至375 ppm,是导致全球气候变暖的主要原因[1]。海洋作为大气CO₂的“汇”之一,每年可吸收人类释放CO₂气体总量的30%,对全球碳循环的收支平衡有重要作用[2]。两极地区是CO₂的主要汇区,也是全球变化的重要反馈窗口。因此,了解碳在北冰洋的生物地球化学循环过程是十分必要的[3-4]。海洋中的生源沉积物主要来自于海洋上层浮游生物碎屑的沉降,主要由蛋白石(以生物硅代替,BSi)、碳酸钙(CaCO₃)和有机质(通常用有机碳替代,TOC)组成[5]。     

Temporal variation in mass fluxes and the major components of sinking particles in Sagami Bay, off Japan

Sinking particles were collected using time-series sediment traps deployed at 350 and 20 mab at Site SB (34° 58.5’N, 139° 20.9’E, 1544 m depth) near the center of Sagami Bay, off Japan with high time resolutions of 5-8 days (March 1997 to August 1998) and 3-4.5 days (March 1998 to August 1998), respectively. The major components (CaCO₃, OM, opal, and clay) of these sinking particles and surface bottom sediments were determined using a stepwise leaching method combined with gravimetry. Average total mass fluxes were 1480, 5560 and 3068 mg/m²/year at 350 mab, at 20 mab, and in the surface sediments, respectively, indicating an enhanced collection of sinking particles at 20 mab. Clay was the dominant component and biogenic components (opal+OM+CaCO₃) were dominated mainly by opal and secondly by OM. On average, opal and CaCO₃ contents decreased gradually as clay content increased with increasing depth from 350 mab-20 mab and in the surface sediments, indicating dissolution of opal and CaCO₃ through sinking, rebound, resuspension or sedimentation processes. Thirteen total mass flux peaks at 17--40-day intervals were observed at 350 mab during the period from March 1997 to August 1998 except for winter, while eight peaks were observed at 20 mab for the period from March 1998 to August 1998. Two types of total mass peaks can be distinguished: one with a clear increase in biogenic flux (opal+OM+CaCO₃) and little or no increase in clay flux and termed a bloom type (B-type), and the other with a clear increase in clay flux, little increase in biogenic flux and termed a resuspension type (R-type). Some R-type peaks, but not all, coincided with total mass flux peaks observed at the mouth of Tokyo Bay and suggested the possibility of the effect of particulate materials transported from Tokyo Bay to site SB. The enormously large peak observed at 20 mab in late May 1998 and that at 350 mab in early June 1998 were considered to be due to some physical perturbations from an earthquake swarm near site SB during the period from April to June 1998. The 17--40-day periodicity was associated clearly with the change in biogenic flux dominated by opal flux and is thought to reflect the periodicity of biological productivity dominated by diatoms in the euphotic zone of Sagami Bay.     

The solid state speciation of copper in surface water particulates and oceanic sediments

A sequential leaching technique has been used to characterize the solid state speciation of total copper (∑Cu) among a number of operationally defined host fractions in surface seawater particulates from the Atlantic Ocean, a diagenetically active hemipelagic sediment core from the eastern Mediterranean, a turbidite - rich sediment core from the Madeira Abyssal Plain and a series of 79 Atlantic Ocean surface or near surface sediments. Around 50% of the ∑Cu in the surface water particulates is held in organic associations. When the material is deposited at the sediment surface, following its entry into the down-column carbon flux, the ∑Cu undergoes phase transformations as the organic carriers are destroyed. However, some of the organically associated copper (Cu₅) is preserved in the sediments, the amount depending on the diagenetic environment of deposition. The relationship between ∑Cu and organic carbon in an oceanic sediment may be masked, but the partitioning speciation data has shown that good correlations can be found between organic carbon and Cu₅. The concentration of Cu₅ in Atlantic Ocean surface sediments is highest in hemipelagic (diagenetically active) sediments deposited in the marginal regions, and lowest in open-ocean (less diagenetically active) sediments of the Mid-Atlantic Ridge and ridge flanks. The marginal sediments contain an average of 20% of their total Cu in an organic association, with the result that these sediments can act as traps for seawater-derived Cu that would normally be regarded as being ‘reactive’ in the marine environment. To a first approximation, the preservation of Cu₅ in the sediments mimics that of primary production in the overlying waters, and so ‘fingerprints’ the operation of the global ocean carbon flux in oceanic deposits. However, the relationship can be perturbed by the off-shelf transport of organic-rich, Cu₅-containing, turbidites which can result in the transfer and burial of organic copper host fractions in open-ocean oxic environments.     

Metal fluxes to the sediments of the northern Venice Lagoon

Eighteen short cores were analyzed for major and trace metals (Al, Fe, Ca, Mg, Mn, Si, K, Ti, Pb, Zn, Cu, Ni, Cr), ²¹⁰Pb, ¹³⁷Cs, and other sediment characteristics, so as to describe the chronology of pollution and calculate metal concentration factors and fluxes. Substantial evidence was found that trace metal profiles are influenced by anthropogenic sources and by changes in sediment composition. Only Zn presents concentrations (up to 13.1 μmol g⁻) and concentration factors (1.3 to 13.2) that can be attributed to heavy contamination. Pb, Cu and Ni, in this order, are less significant. The areal distribution of concentrations and inventories reflects the importance of direct sources, in particular the industrial area of Porto Marghera and the Dese river. The inventories of excess metals, above pre-industrial levels, were determined for each core and the three different parts of the study area, the amounts of Zn accumulated in sediments are 11.0 Mmol, 5.1 Mmol and 0.37 Mmol in the Campalto, S. Erasmo, and Palude di Cona areas, respectively. Ruxes were also calculated and compared with those suggested for the atmospheric delivery by Cochran et al. [(1995)b. Atmospheric fluxes of heavy metal contaminants to the Venice Lagoon, Rapp. Comm. Int. Mer Médit., 34, 136.], the atmospheric contribution is predominant or significant in many cases, especially at sites far from the major local inputs. Concentrations and fluxes show a significant increase in the anthropogenic metal supply starting from the second decade of this century, with maximum inputs in the period between the (1930)s and the (1970)s. At some stations a decrease in heavy metal contamination of surficial sediments was found and this could be ascribed to a reduced input of pollutants in recent years.     

Heavy metals in sinking particles and bottom sediments from the eastern Turkish coast of the Black Sea

Concentrations of Cd, Cu, Cr, Co, Ni, Zn, Fe, Mn, Pb, As, and Sb were determined in sediment trap and bottom sediment samples collected seasonally from a station on the eastern Turkish coast of the Black Sea. Cd, Pb and Mn concentrations were highest in the sediment trap samples except during the summer period, whereas Co, Ni, Zn and Fe levels were much lower than corresponding levels found in the surface sediments. Cu, Cr, As and Sb levels showed no definite trend with sediment type. In general, with the exception of Cr, relatively lower metal concentrations in the sediment trap material were determined in the summer period. The highest mass flux, 56.5 g m⁻² day⁻¹, was measured during autumn. The highest flux of heavy metals also occurred during autumn and was strongly dependent on particle mass flux. Based on these results, we suggest that the downward vertical transport of particulate heavy metals in this region is related to the high degree of land erosion and the resultant particulate flux dynamics, which occur here. It was noteworthy that the highest concentrations of Cd, Cu, Co, Zn, Fe and Sb in particles were measured during winter a finding which suggests that enhanced fossil fuel combustion, which occurs during this period in adjacent urban and industrial areas plays an important role in the metal composition of sinking particles in nearshore waters.     

西北冰洋表层沉积物中生源和陆源粗组分及其沉积环境

通过中国第1至第3次北极科学考察在北冰洋西部所采集的99个表层沉积物中生源与陆源粗组分的分析,研究了该海域表层生产力的变化,有机质来源以及陆源粗颗粒物质的输入方式和影响因素.研究区域生源组分所反映的表层生产力变化与通过白令海峡进入楚科奇海的3股太平洋洋流密切相关.楚科奇海西侧高盐高营养盐的阿纳德尔流流经区域,表层生产力...