Effects of oxic and anoxic filtration on determined methyl mercury concentrations in sediment pore waters

Accurate determination of methyl mercury (MeHg) concentrations in sediment pore waters is crucial for an improved understanding of mercury (Hg) biogeochemistry, and for improved risk assessment of Hg contaminated sites. In the present study, effects of oxic (air) and anoxic (N₂) filtration (after centrifugation) on determined pore water MeHg concentrations were investigated in severely Hg contaminated pulp fibre sediments from two estuaries of the Bothnian Sea, Sweden. MeHg was determined in the filtrate using species-specific isotope dilution gas chromatography inductively coupled plasma mass spectrometry (SSID–GC–ICPMS), after ethylation with sodium tetraethylborate. Determined concentrations of MeHg were greater after anoxic filtration than after oxic filtration for all samples investigated, with MeHg(N₂)/MeHg(air) ratios ranging between 3.4 and 343. Adsorption to newly formed Fe(III)/Mn(III/IV)-oxy/hydroxide surfaces is proposed as the main mechanism responsible for MeHg removal during oxic filtration. This is supported by decreases in dissolved Fe and Mn concentrations during oxic filtration, and by decreases in dissolved sulphur concentrations during oxic filtration in the samples with largest effect on MeHg concentrations. The latter is explained by adsorption of SO₄²⁻ to newly formed Fe(III)/Mn(III/IV)-oxy/hydroxide surfaces. The effect of oxidation during filtration on pore water MeHg concentrations was largest in samples in which FeS(s) was not present, but with calculated pe-values below − 3. Thus, our results indicate that the largest errors with respect to pore water MeHg concentrations when filtering in air can be expected in samples with an intermediate redox potential, possibly buffered by a mixture of oxidation sensitive Fe(II/III) minerals.     

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.     

Some peculiarities of the trace-metal distribution in Baltic waters and sediments

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.     

Trace element diagenesis in pyrite-rich sediments of the Achterwasser lagoon, SW Baltic Sea

The early diagenesis of trace elements (V, Cr, Co, Cu, Zn, As, Cd, Ba, U) in anoxic sediments of the Achterwasser, a shallow lagoon in the non-tidal Oder estuary in the Baltic Sea, was investigated in the context of pyrite formation. The dissolved major redox parameters show a two-tier distribution with transient signals in the occasionally re-suspended fluid mud layer (FM) and a permanently established diagenetic sequence in the sediment below. Intense microbial respiration leads to rapid depletion of O₂ within the uppermost mm of the FM. The reduction zones of Mn, Fe and sulfate overlap in the FM and in the permanently anoxic sediment section which appears to be a typical feature of estuarine sediments, under low-sulfate conditions. Degrees of pyritization (DOP) range from 50% in the FM to remarkably high values > 90% at 50 cm depth. Pyrite formation at the sediment surface is attributed to the reaction of Fe-monosulfides with intermediate sulfur species via the polysulfide pathway. By contrast, intense pyritization in the permanently anoxic sediment below is attributed to mineral growth via adsorption of aqueous Fe-sulfide complexes onto pyrite crystals which had originally formed in the surface layer.The studied trace elements show differential behavior patterns which are closely coupled to the diagenetic processes described above: (i) Zn, Cu and Cd are liberated from organic matter in the thin oxic layer of the sediment and diffuse both upwards across the sediment/water boundary and downwards to be trapped as monosulfides, (ii) V, Cr, Co and As are released during reductive dissolution of Mn- and Fe-oxyhydroxides, (iii) U removal from pore water occurs concomitantly to Fe reduction in the FM and is attributed to reduction of U(VI) to U(IV), (iv) the Ba distribution is controlled by reductive dissolution of authigenic barite in the sulfate reduction zone coupled with upward diffusion and re-precipitation. The incorporation of trace elements into pyrite is most intense for Co, Mn and As, intermediate for Cu and Cr and little to negligible for U, Zn, Cd, V and Ba. The observed trend is largely in agreement with previous studies and may be explained with differing rates for ligand exchange. Slow and fast ligand exchange and thus precipitation kinetics are also displayed by downcore increasing (Mn, Cr, Co and As) or constantly low (Zn, Cu, Cd) pore water concentrations. The downward increasing degrees of trace metal pyritization (DTMP) for Co, Cu, Zn and As are, in analogy to pyrite growth, assigned to adsorption of sulfide complexes or As oxyanions onto preexisting pyrite minerals.     

Live foraminiferal faunas from a 2800 m deep lower canyon station from the Bay of Biscay: Faunal response to focusing of refractory organic matter

A 2800 m deep station was sampled on three occasions, in January 1999, June 1999 and April 2000, in the lower part of Cap-Ferret Canyon (Bay of Biscay). This area is characterised by a rapid accumulation of fine-grained sediments and by important inputs of reworked organic matter in an intermediate state of decay. Diagenetic reactions within the sediment follow the well-established depth sequence resulting from the oxidation of organic deposits by different electron acceptors. At our station, live benthic foraminiferal faunas differ strongly from faunas previously collected at nearby open slope sites at a comparable water depth. Spectacularly high densities of deep infaunal species are observed in the deeper parts of the sediment for all three sampling periods. In our opinion, these high deep infaunal densities are a direct response to the massive flux of partially degraded organic matter, which is slowly introduced into the deeper parts of the sediment, where it induces a rather stable succession of redox gradients. Melonis barleeanus lives in the dysoxic part of the sediment whereas Globobulimina affinis appears preferentially close to the zero oxygen boundary. Both taxa occupy niches where the highest content of Mn (III, IV)-oxides and -oxihydroxides and Fe (III)-oxides are recorded. The fact that most of the geochemical reactions within the sediment are directly or indirectly catalysed by heterotrophic and chemolithoautotrophic bacterial consortia could suggest that deep infaunal foraminifera may be highly specialised protozoans able to feed on, or live in symbiosis with these prokaryotic communities.     

Sediment-water exchange of Mn,Fe, Ni and Zn in Galveston Bay,Texas

In-situ benthic flux studies were conducted at three stations in Upper Galveston Bay twice during March 1996 to directly measure release rates of dissolved Mn, Fe, Ni and Zn from the sediments. Results showed reproducible increases with time in both replicate light and light–dark benthic chambers, resulting in average fluxes of −1200±780, −17±12, −1.6±0.6 and −2.4±0.79 μmol m⁻² day⁻¹ for Mn, Fe, Ni and Zn, respectively. Sediment cores collected during 1994–1996 showed that surficial pore water concentrations were elevated compared to overlying water column concentrations, suggesting diffusive release from the sediments. Diffusive flux estimates of Mn and Zn agreed in direction with chamber fluxes measured on the same date, but only accounted for 5–38% of the measured flux. Diffusive fluxes of Fe agreed with measured fluxes at the near Trinity River station but overestimated actual release in the mid and outer Trinity Bay regions, possibly due to inaccurate determination of the Fe pore water gradients or rapid oxidation processes in the overlying water at these stations.In general, measured fluxes of Mn and Ni were higher in the mid Trinity Bay region and suggested a mechanism for the elevated trace metal concentrations previously reported for this region of Galveston Bay. However, the fluxes of Fe were highest in close proximity to the Trinity River, supporting the elevated Fe concentrations measured in this region during this and other studies, and decreased towards middle and outer Trinity Bay. Trace metal turnover times were between 0.1 and 1.2 days for Mn, between 1.3 and 4.6 days for Fe, and between 27 and 100 days for Ni and 12–20 days Zn, and were considerably shorter than the average Trinity Bay water residence time (1.5 years) for this period. Comparing area averaged benthic inputs to Trinity River inputs shows the sediments to be a significant source of trace metals to Galveston Bay. However, while benthic inputs of trace metals were measured, water column concentrations remained low despite rapid turnover times for Mn and Fe, suggesting removal of these metals from the water column after release from the sediments.     

Phosphorus regeneration and burial in near-shore marine sediments (the Gulf of Trieste, northern Adriatic Sea)

According to bioassay studies and high dissolved nutrient N/P ratios in the seawater column, phosphorus (P) is thought to control marine productivity in the northern Adriatic Sea. P in near-shore marine sediments of the Gulf of Trieste, the northernmost part of the Adriatic Sea, was investigated using pore water P distributions, and benthic P flux studies under oxic and anoxic conditions. The data show that P regeneration is up to three-fold more extensive in sediments overlain by oxygen-depleted waters and proceeds in parallel with Fe and Mn enhanced benthic fluxes. It appears from the incubation experiments that degradation of sedimentary organic matter is the main contribution to the flux of P at the sediment–water interface, while the release of phosphate adsorbed on the iron oxide surface is of minor importance.It appears that about 50% of P in the Gulf of Trieste is retained within in the sediments, probably bonded to clay minerals and carbonate grains or precipitated as fluoroapatite. In these sediments total P (P_tot) is preserved preferentially over organic C (C_org). P regenerated from surficial sediments contributes about 1/3 of the P that is assimilated by benthic microalgae. The phytoplankton P requirement should be entirely supplied from fresh-water sources. These results suggest that oxygen depletion in coastal areas caused by eutrophication enhances P regeneration from sediments, providing the additional P necessary for increased biological productivity. The development of anoxic bottom waters in coastal areas enhances the recycling of P, exacerbating the nutrient requirement in the area. A geochemical record of P burial in a longer sedimentary sequence revealed an increasing trend of P_tot and organic P (P_org) contents occurring approximately 50 years BP (after 1950), probably due to increasing use of inorganic fertilizers and detergents in the area.     

The geochemistry of iron and manganese in the waters and sediments of Bolstadfjord,S.W. Norway

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).     

用细化的铁形态分析及量化的铁氧化物活性表征海洋沉积物中铁的成岩作用：以胶州湾为例

以富营养化的胶州湾一个柱状沉积物为例,用细化的铁形态分析及量化的铁氧化物还原活性相结合的方法研究了沉积物中铁的成岩作用过程。结果表明,这两种方法相结合的结果能更详细示踪铁的转化并能从多视角提供铁成岩作用的细微差别。这一方法有望应用于其它研究中更好地揭示复杂的铁和硫的生物地球化学循环。铁微生物还原在上部沉积物铁的还原中起重要作用,但12 cm深度以下铁被硫化物的化学还原为主要过程。最具生物活性的无定形铁氧化物是铁微生物还原的主要参与者,然后依次为弱晶态铁氧化物和磁铁矿,晶态铁氧化物几乎不参与铁的成岩循环。沉积物上部铁微生物还原的重要作用主要是活性铁含量高而活性有机质含量低共同作用的结果,且后者也是沉积物中硫酸盐还原速率以及硫化物积累的最终制约因素。对比研究表明,通过还原性溶解动力学方法表征的微生物可还原的铁氧化物主要由无定形和弱晶态铁氧化物组成,其总体活性常数相当于老化的水铁矿,且随深度增加而减低。     

The Distribution and Redox Chemistry of Iron in the Pettaquamscutt Estuary

A series of high resolution (10 cm) vertical profiles of iron were determined across the oxic/anoxic boundary in the Lower Pond of the Pettaquamscutt Estuary. Selective chemical treatments and multiple analytical methods were used to detemine the oxidation state and lability of iron across the oxic/anoxic boundary. The vertical distributions of dissolved and total iron were determined by atomic absorption spectroscopy, and dissolved Fe(II) and reducible iron were determined using a modified Ferrozine spectrophotometric method. Well-developed maxima of total dissolved iron ≈7·5 μM occurred within the oxic/anoxic transition zone. Analysis of Fe(II) by the FZ method indicates that more than 95% of the dissolved iron determined by atomic absorption spectroscopy within the maximum is in the form of Fe(II). The concentration of dissolved Fe(II) ranged from <4 nM in oxygenated surface waters to between 7 and 8 μM at the total dissolved iron maximum.Both dissolved and total iron samples were treated with ascorbic acid to quantify the fraction of iron that was reducible in this system. Dissolved iron is quantitatively reduced to Fe(II) by 3·5 m depth, and particulate iron was almost completely dissolved by 6 m. Thermodynamic speciation calculations indicate that the dominant species of Fe(II) in the anoxic waters is the Fe(HS)⁺complex. In addition, the concentration of Fe(II) in the anoxic zone appears to be controlled by precipitation of a sulfide phase, the ion activity product for waters below 7 m is in good agreement with the solubility product of mackinawite.The vertical distribution of oxidation states of the metals indicates non-equilibrium conditions due to microbiological and chemical processes occurring in the redox transition zone. A one-dimensional vertical, eddy diffusion model is presented that incorporates redox reactions of iron, sulfide and oxygen. The modeling suggests the maximum in Fe(II) can be achieved through inorganic oxidation and reduction reactions, however the depth at which the maximum occurs is sensitive to sulfide oxidation, which appears to be dominated by biological oxidation. The magnitude of the Fe(II) maximum depends on the flux of iron into the basin, and reductive dissolution of particulate iron.     

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.     

东、黄海沉积物-水界面营养盐交换速率的研究

2000年10月和2001年5月随“东方红2号”考察船在东、黄海进行考察,在A2、E2、E4、E5、E65个站位作了培养实验,研究沉积物-水界面在氧化和还原条件下的交换通量。在东海海域,NO3-、PO43-、总磷(TDP)由水向沉积物中扩散,NH4 、SiO32-由沉积物向水中扩散,NO3-、TDP、NH4 在还原条件下的交换通量大于氧化条件下的交换通量,PO43-、SiO32-在氧化还原条件下的交换通量基本一致。在黄海海域,两站位各溶解态营养盐的迁移方向有较大差异。在距离陆地较近的海域,各溶解态营养盐多由水中向沉积物中扩散,且距离陆地越近,交换通量越大。在东、黄海海域,沉积物释放的SiO32-对初级生产力的贡献分别为13%、10%~18%,与河流输送和大气沉降相比,沉积物对黄海、东海SiO32-的贡献分别占90%、86%,说明沉积物是SiO32-的源。而在整个东、黄海海域,对于溶解无机氮(DIN)和PO43-来说,它们的交换通量为负值,即沉积物从水体中吸附溶解无机氮和磷,说明沉积物是DIN和PO43-的汇。     

The distributions of uranium, radium and thorium isotopes in two anoxic fjords: Framvaren Fjord (Norway) and Saanich Inlet (British Columbia)

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.     

Reactive iron in Black Sea Sediments: implications for iron cycling

The distribution of reactive iron in sediments of the northwestern shelf, the shelf edge and the abyssal part of the Black Sea has been studied. In the euxinic Black Sea, iron sulfides (pyrite and iron monosulfide) are formed in the upper part of the anoxic water column and sink to the deep-sea floor where they are buried in the sediment. This flux of iron sulfides from the water column is reflected in enhanced concentrations of highly reactive iron and a high degree of pyritization (0.57–0.80) for the deep-water sediments of the Black Sea. The iron enrichment of deep-water sediments is balanced by a loss of highly reactive iron from the oxic continental shelf. Calculations from a numerical diagenetic model and reported in situ flux measurements indicate that the dissolved iron flux out of the shelf sediments is more than sufficient to balance the enrichment in reactive iron in deep-sea sediments, and that the majority of the dissolved iron efflux is redeposited on the continental shelf. This iron mobilization mechanism likely operates in most shelf areas, but its net effect becomes only apparent when reactive iron is trapped in sulfidic water bodies as iron sulfides or when iron is incompletely oxidized in low oxygen zones of the ocean and transported over long distances.     

Dissolved organic carbon in sediments from the eastern North Atlantic

Profiles of dissolved organic carbon (DOC) were measured in the pore water of sediments from 1000, 2000 and 3500 m water depth in the eastern North Atlantic. A net DOC accumulation in the pore waters was observed, which followed closely the zonation of microbial respiration in these sediments. The concentration of pore water DOC in the zone of oxic respiration was elevated relative to that in the bottom ocean water. The resulting upward gradient across the sediment–water interface indicated a steady state diffusive benthic flux, F_DOC, of 0.25–0.44 mmol m⁻² day⁻¹ from these sediments. Subsequent increase in the concentration of DOC in the pore water occurred only in the sediments from 1000 and 2000 m water depth that supported anoxic respiration, leading to a deep concentration maximum. By contrast, in the sediments from 3500 m water depth, a deep concentration minimum was measured, coincident with minimal postoxic respiration in this near-abyssal setting. The gradient-based F_DOC represented approximately 14% of the total remineralized organic carbon (TCR=sum of F_DOC and depth-integrated organic carbon oxidation rate) in the sediments from 1000 and 2000 m water depth, while it was 36% of the TCR in the sediments from 3500 m water depth. A covariance of particulate organic carbon (POC) and pore water DOC with depth in the sediments was evident, more consistently at the deepest site. While the covariance can be related to biotic processes in these sediments, an alternative interpretation suggests a possible contribution of sorption to the biotic control on sedimentary organic carbon cycling. The steady state diagenetic conditions in which this may occur can be conceivable for some organic-poor deep-sea locations, but direct evidence is clearly required to validate them.     

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...     

莱州湾游泳动物群落结构研究

本文根据2010和2011年春季（5月）、夏季（8月）、秋季（10月）和冬季（12月）进行的8航次调查数据，研究了莱州湾游泳动物群落格局及其与环境因子关系。结果显示，调查共捕获游泳动物85种，2011年生物量略高于2010年；生物量季节间差别较大，各季节生物量排序为夏季、秋季、冬季和春季；不同年间相同季节生物量差异多不显著（秋季除外）；除2010年春季外，其余季节均为鱼类生物量最高，甲壳类次之，头足类最低；从全年调查平均值来看，莱州湾西侧游泳动物生物量（60.2 kg/h）明显高于东侧（33.4 kg/h）。根据8航次31个主要种类生物量聚类分析，莱州湾20调查站位可划分为4组：组I由位于调查海域东南的3个站位组成，组II由位于调查海域东部及中部的8个站位组成，组III由调查海域西北部（黄河口南侧）的3个站位组成，组IV由西部6个站位组成。组I浮游植物丰度、浮游动物生物量、游泳动物生物量和游泳动物多样性指数在各组中均最低，而底栖动物生物量最高；组III和组IV的浮游植物丰度、浮游动物生物量以及游泳动物生物量高于组I和组II。ANOSIM分析表明，各聚类组间群落结构虽有不同，但差异并不显著。DCCA分析表明，温度、盐度、底栖动物生物量以及浮游植物丰度是影响游泳动物群落的重要因子。研究表明，目前莱州湾游泳动物群落总生物量处于较低水平，特别是春季生物量下降尤为严重；生物量的季节分布发生了较大的改变，春季生物量极低，夏季生物量相对较高；底层鱼类比例下降的趋势有所逆转，头足类比例明显增加。莱州湾游泳动物群落格局异质性较低，可能与莱州湾生境异质性低以及人类剧烈干扰密切相关。     

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.     

厌氧沉积中有孔虫组合特征

厌氧沉积的有孔虫组合中,底栖有孔虫主要由Bolivina诸种和Buliminella tenuata组成,同时含有少量厌氧标志种Suggrunda eckisi;浮游有孔虫中以Globigerrina bulloides和G.quingueloba为数较多。底栖有孔虫与浮游有孔虫数量相比,浮游有孔虫数量很少。