Distribution and quality of sedimentary organic matter on the Aquitanian margin (Bay of Biscay)

During the ECOFER experiment (French ECOMARGE program), surficial sediments were sampled on the Aquitanian margin with box corers and analyzed to determine the quantity and quality of organic matter. Sediments from the margin are enriched in organic carbon (mean value 1.35%) in comparison to deep-sea and shelf sediments, due to a fine grain-size sedimentation. As sedimentation rates are high, the margin appears to be an organic depocenter. Some preferential organic enrichment zones were identified in the Cap-Ferret Canyon. There is a supply of continental material from the Gironde estuary, but marine contribution seems more possible than Adour or spanish rivers. No seasonal variations of organic matter were observed at the surface of sediments, suggesting mineralization processes of labile organic matter: average organic carbon consumption was evaluated to 9.0 g C m⁻² yr⁻¹. Rapid biological mineralization processes are lower than on the Mediterranean margin, mainly related to significant differences in water temperature. The great width of the canyon, its distance from the continent, and the current circulation pattern prevent any precise recording of the variable organic inputs to the sediment and favor nepheloı̈d transport, resuspension and shelf break processes, which wipe out any print of fresh material input. An organic carbon budget indicates that an equilibrium between organic inputs and organic mineralization+accumulation is not obtainable. The supply of suspended matter could have been minor during the year in question, and sedimentation rates are still imprecise.     

Monitoring suspended particulate matter fluxes and patterns with the AVHRR/NOAA-11 satellite: application to the Bay of Biscay

AVHRR/NOAA-11 satellite images of the C1 (580–680 nm) and C2 (725–1100 nm) channels were used to quantify the suspended particulate matter discharged into the ocean by the Gironde estuary (France). The calibration method is based on a comparison between satellite values (AVHRR reflectances) and suspended particulate matter (SPM) concentrations at the sea surface, measured in situ. To correct the aerosol variations a C1-C2 image subtraction is applied. However, when the SPM concentration is greater than about 15 mg l⁻¹, the C2 channel image is affected by water turbidity and the C1-C2 correction cannot be used. The C1 channel is more sensitive, and we were able to distinguish SPM concentration variations greater than 0.5 mg l⁻¹. A subtraction of two images recorded with a 24 h interval was carried out to evaluate vertical and horizontal fluxes. The residual image shows the quantity of particles leaving the surface layer. To assess horizontal displacements, turbid fronts were mapped by means of an image gradient analysis. Major and minor fronts recorded each day, superimposed to outline displacements (gradients and orientations), were displaced from the Gironde estuary to the West and the Northwest.During the ECOFER cruises (1989–1991), several AVHRR scenes were processed using an atmospheric correction based on the low SPM concentrations (“ocean pixel subtraction”). Generally, surface particulate matter is confined to the inner continental shelf. Higher values were observed during the ECOFER 4 cruise. Suspended particulate matter concentrations with the maximum extension appeared during the ECOFER 1 cruise. Concentrations were very low during the ECOFER 5 cruise, even in the lower estuary. This was due to low summer discharges that occurred during the dry period of 1988–1991 in France. During these surveys, estimated SPM concentrations were less than 1.5 mg l⁻¹ in the ECOFER area.     

Fronts and transport of suspended matter in the Hangzhou Bay

A persistent, year-round NE-SW front is found to exist inside the Hangzhou Bay. This front is actually the merging of the secondary Changjiang plume front from the bay mouth and the Qiantang plume front from the upstream side of the bay. During neap tides low runoff periods these two plumes can readily be identified. Our findings suggest that suspended matter is transported into the bay through the north end by the secondary Changjiang plume. The front inside the bay acts the part of concentrating suspended matter, and also plays an important role in both the fine-grained sediment and heavy metal distributions in this sedimentary basin.     

Fine-grained sediment budget on the continental margin of the Bay of Biscay

Under present-day conditions, rivers are the main source of fine sediments dispersed to the Bay of Biscay. They deliver about 2.5×10⁶ t yr⁻¹ of continental fine sediments, 60% of which is derived from the Gironde estuary. Of this flux, 65% is believed stored on the shelf. Two kinds of mud fields can be found in the Bay of Biscay: coastal mud and shelf mud belts. The total mass of fine sediments stored during the past 2000 years is 3.2×10⁹ t. Consequently, about 0.9×10⁶ t yr⁻¹ could reach the shelf edge and eventually the open sea. From this amount of displaced material and the deposition surface areas, an evaluation of sediment fluxes across the margin during the late Holocene period is discussed. This evaluation is compared with results obtained from ECOsystéme du canyon du cap-FERret (ECOFER) data from sediment traps and surficial box cores.     

普里兹湾水体悬浮颗粒物天然15N

本文研究了南极普里兹湾海域悬浮颗粒物中的天然15N丰度,并就δ15N与POC、PON等生化要素之间的相关性进行了讨论,对δ15N含量分布特征的形成机制及其与物理、生物学过程的耦合进行了探讨,给出了南极普里兹湾悬浮颗粒物中的δ15N与POC、PON含量呈负相关关系;表层水中δ15N、POC和PON的分布和δ15N的垂直分布可能与涡流有关.     

南极普里兹湾及其邻近海域悬浮颗粒有机物的碳同位素组成及其影响因素

依托中国第29次南极科学考察航次开展了南大洋普里兹湾及其邻近海域悬浮颗粒有机物碳同位素组成(δ13CPOC)的研究,结合温度、盐度、营养盐和溶解CO_2的数据,揭示了影响研究海域颗粒有机物碳同位素组成的主控因素,计算出混合层中浮游植物吸收无机碳过程的碳同位素分馏因子。结果表明,普里兹湾及其邻近海域的δ13CPOC介于-28.5‰~-21.1‰,平均值为-24.6‰,表现出湾内大于湾外的特征。浮游植物同化吸收CO_2过程的碳同位素分馏是影响研究海域混合层δ13 CPOC的主要因素,根据δ13CPOC和1/[CO_2(aq)]的线性拟合关系,计算出浮游植物同化吸收CO2过程的碳同位素分馏因子εp为23.4‰。δ13CPOC的垂直分布随深度增加而增大,反映出颗粒有机物垂向输送过程中颗粒有机物再矿化过程同位素分馏作用的影响。     

Distribution of suspended particulate matter in the northern Bohai Bay in summer and its relation with thermocline

Field observations of suspended particulate matter (SPM) in the Bohai Bay, China have not been widely reported. The aim of this paper is to describe the horizontal and vertical distribution of mass and volume concentrations of SPM, respectively, based on observed data at 312 stations in the northern Bohai Bay during summer of 2006. A numerical model ECOMSED coupled with a sediment transport module was also established to further discuss the mechanism of the thermocline effect on the vertical distribution of SPM. The mass concentrations of SPM exhibited high inshore values and low offshore values in the horizontal distribution; while in the vertical direction, characteristics of the volume concentration of SPM can be divided into two types: one with a sharp peak at depth of 10–15 m and another without. The peak value at the depth of the thermocline was resulted from concentrated phytoplankton. A numerical experiment further displayed that the thermocline can also prevent particles from being resuspended upward.     

Measurements of suspended particulate matter with laser in-situ scattering and transmissometry in the Jiaozhou Bay in China

1 IntroductionKnowledge of suspended particle size and distri-bution is the key elements for better understandingthe sediment transport processes ( Wang et al.,2004), primary production (Ning et al., 2004),water quality controlling and pollution predictio…     

A three-dimensional model of suspended particulate sediment transport

Depth-averaged, one-dimensional and two-dimensional numerical models of bed and suspended particulate sediment transport provide unreliable answers for siltation and erosion quantities in situations dominated by three-dimensional flow patterns, as occur in harbour entrances due to flow separation and wind and density currents. Consequently, a numerical scheme has been developed which solves the complete three-dimensional diffusion-advection equation for suspended sediment concentration and thereby makes possible the study of siltation problems in complex, three-dimensional flows. The model analogue is based on a splitting technique and employs a mixed characteristics and finite difference approach. The accuracy and usefulness of the resulting scheme have been investigated by applying it to a number of hypothetical situations and to a laboratory situation involving the transport and dispersal of lightweight sediment. The results of the various tests show that the proposed approach works well and provides a useful basis for the study of practical problems.     

Mineral composition of the suspended particulate matter in the White Sea

The mineral composition of the suspended particulate matter (SPM) was studied for the White Sea area. The comparative analysis of the composition of the marine SMP and the SPM of the rivers of the White Sea catchment area was performed, including the Severnaya Dvina River, one of the major sources of the terrigenous suspended matter to the sea. The research of such kind is faced with numerous methodological difficulties, which slows down the study process. Data on the mineral composition of the SPM are scarce. Applying the method of X-ray powder diffractometry, we assessed the bulk mineral composition of the SPM with special regard to its clay fraction.     

Relationship between hydrology and seasonal distribution of suspended sediments on the continental shelf of the Bay of Biscay

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.     

乐清湾悬沙输移机制分析

以乐清湾海区特征测站实测资料为据,运用机制分解法将悬沙净输移通量分解成多个动力项并讨论不同区域悬沙输移的时空分布特征,认为潮泵输沙在湾内贡献均较大,在浅滩附近占明显优势,垂向净环流输沙在小潮期中,内湾作用显著,平流输沙在开阔水域及中湾深槽起主要作用.从余流分布、流速与含沙量的相位关系、垂向余流结构与悬沙浓度垂向梯度变化...     

夏季大亚湾悬浮颗粒有机物碳、氮同位素组成及其物源指示

2015年夏季开展了大亚湾悬浮颗粒有机物碳（POC）、氮含量（PN）及其同位素组成的研究,结果表明,δ13C_POC和δ15N_PN的变化范围分别为-25.7‰~-17.4‰和-6.3‰~10.4‰,平均值分别为-20.2‰和8.2‰。大亚湾悬浮颗粒有机物含量及其碳氮同位素组成的空间变化反映了不同有机质来源的影响:喜洲岛附近海域表现出高POC、PN、δ13C_POC和δ15N_PN的特征,指征着浮游植物水华的主导贡献;东北部范和港附近海域具有高POC、PN、低δ13C_POC和高δ15N_PN的特征,反映了河流/河口水生有机物的影响;湾顶白寿湾附近海域的δ13C_POC和δ15N_PN出现低值,体现了陆源有机质和人类污水排放的影响。借助δ13C_POC和δ15N_PN的三端元混合模型,定量出海洋自生有机质、陆源有机质、河流/河口水生有机质等3个来源的贡献平均分别为70%、13%和17%,其中海洋自生有机质是夏季大亚湾悬浮颗粒有机物的最主要来源。从这3种来源颗粒有机物含量的空间变化看,海洋自生有机质含量由湾内向湾外减少,与初级生产力的空间变化相对应;河流/河口水生有机质含量在大亚湾东北部出现高值;陆源有机质含量在表、底层出现不同态势,表层陆源有机物含量在湾中部海域最低,而底层则呈现出自湾内向湾口增加的趋势,主要受控于离岸距离和珠江冲淡水、粤东沿岸上升流输送的影响。     

A study of the geochemistry of suspended particulate matter in coastal waters

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.     

湄洲湾峰尾围垦工程施工期间海水悬浮泥沙输移扩散的数值模拟

围填海工程施工过程导致海域悬浮物迅速增加,影响周围海洋生态系统,研究围填海工程悬浮泥沙的输移扩散规律对于区域生态环境质量及工程建设的综合生态影响评价具有重要的参考意义．针对湄洲湾峰尾围垦工程施工期悬浮泥沙可能造成的生态影响,对爆破挤淤（5．17t／s）和抛石挤淤（1．39kg／s）的悬沙源强进行了分析计算．在工程海区平面二维潮流场数学模型的基础上,采用二维对流扩散数学模型对施工范围内的模型网格点（40m×40m）进行了逐点计算,数值模拟结果表明,悬浮泥沙扩散范围和形态主要受潮流控制,工程施工联合影响下悬沙质量浓度大于10mg／dm3的全潮最大影响包络面积为5．848km2,施工9h后悬沙影响基本消失,为工程施工期环境管理提供了参考依据．施工悬浮泥沙的扩散整体表现为总悬沙质量浓度在离工程区较近的范围内较大,而距离越远质量浓度越接近自然状态的本底含沙量．施工悬浮泥沙对浮游生物、游泳生物和底栖生物等均会产生一定的影响,但随着施工结束而消失,不会对海洋生态产生长期的不利影响．     

Molecular and isotopic constraints on the sources of suspended particulate organic carbon on the northwestern Atlantic margin

The abundance, carbon isotopic composition (Δ¹⁴C and δ¹³C), and lipid biomarker (alkenones and saturated fatty acids) distributions of suspended particulate organic matter were investigated at three stations centered on the 2000, 3000, and 3500 m isobaths over the New England slope in order to assess particulate carbon sources and dynamics in this highly productive and energetic region. Transmissometry profiles reveal that particle abundances exhibit considerable fine structure, with several distinct layers of elevated suspended particulate matter concentration at intermediate water depths in addition to the presence of a thick bottom nepheloid layer at each station. Excluding surface water samples, the Δ¹⁴C values of particulate organic carbon (POC) indicated the presence of a pre-aged component in the suspended POC pool (Δ¹⁴C<+38‰). The Δ¹⁴C values at the 3000 m station exhibited greater variability and generally were lower than those at the other two stations where the values decreased in a more systematic matter with increasing sampling depth. These lower Δ¹⁴C values were consistent with higher relative abundances of terrigenous long-chain fatty acids at this station than at the other two stations. Two scenarios were considered regarding the potential provenances of laterally transported POC: cross-shelf transport of shelf sediment (Δ¹⁴C=?140‰) and along-slope transport of the slope sediment proximal to the sampling locations (Δ¹⁴C=?260‰). Depending on the scenario, isotopic mass balance calculations indicate allochthonous POC contributions ranging between 15% and 54% in the meso- and bathy-pelagic zone, with the highest proportions at the 3000 m station. Alkenone-derived temperatures recorded on suspended particles from surface waters closely matched in-situ temperatures at each station. However, alkenone-derived temperatures recorded on particles from the subsurface layer down to 250 m were lower than those of overlying surface waters, especially at the 3000 m station, implying supply of phytoplankton organic matter originally produced in cooler surface waters. AVHRR images and temperature profiles indicate that the stations were under the influence of a warm-core ring during the sampling period. The low alkenone-derived temperatures in the subsurface layer coupled with the lower Δ¹⁴C values for the corresponding POC suggests supply of OC on resuspended sediments underlying cooler surface waters distal to the study area, possibly further north or west. Taken together, variations in Δ¹⁴C values, terrigenous fatty acid abundances, and alkenone-derived temperatures among the stations suggest that input of laterally advected OC is a prominent feature of POC dynamics on the NW Atlantic margin, and is spatially heterogeneous on a scale smaller than the distance between the stations (<150 km).