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1.
Tj. C. E. van Weering I. R. Hall H. C. de Stigter I. N. McCave L. Thomsen 《Progress in Oceanography》1998,42(1-4)
To quantify recent sediment accumulation, carbon fluxes and cycling, three N.W. European Continental Margin transects on Goban Spur and Meriadzek Terrace were extensively studied by repeated box- and multicore sampling of bottom sediments. The recent sediment distribution and characteristics appear directly related to the near-bed hydrodynamic regime on the margin, which at the upper slope break on the Goban Spur results in along-slope and periodic off-slope directed transport of particles, possibly by entrainment of particles in a detached bottom or intermediate nepheloid layer. From the shelf to the abyssal plain the surface sediments on the Goban Spur change from terrigenous sandy shelf sediments into clayey silts. 210Pb activity decreases exponentially down core, reaching a stable background value at 10 cm (shallower stations) to 5 cm (deeper stations) sediment depth. 210Pb profiles of repeatedly sampled stations indicate negligible annual variability of mixing and flux. The 210Pbxs flux to the sediment shows a decreasing trend with increasing water depth. Below about 2000 m the average 210Pbxs flux is about 0.3 dpm cm−2 y−1, a third of the fluxes measured on the shelf and upper slope stations. Sediment mixing rates (Db) correlate with macro- and meiofaunal density changes and are within the normal oceanic ranges. Lower mixing rates on the lower slope likely reflect lower organic carbon fluxes there. Mass accumulation rates on Meriadzek Terrace are at maximum 80 g m−2 y−1, almost twice as high as at Goban Spur stations of comparable depth. A minimum accumulation rate of 16.6 g m−2 y−1 is found at the Goban Spur upper slope break. Organic carbon burial rates are low compared to other margins and range from a lowest value of 0.05 g m−2 y−1 at the upper slope break to 0.11 g m−2 y−1 downslope. A maximum organic carbon burial rate of 0.41 g m−2 y−1 is found on Meriadzek Terrace. Carbonate burial rates increase along the northern transect from the shelf (13 g m−2 y−1) via a low (9.3 g m−2 y−1) on the upper slope break to the deep sea (30.7 g m−2 y−1). Carbonate burial is highest on Meriadzek Terrace (44.5 g m−2 y−1). The N.W. European Margin at Goban Spur and Meriadzek Terrace cannot be considered a major carbon depocenter. 相似文献
2.
Meiofauna and macrofauna communities and several sediment characteristics were compared between a slope situated far from the coast (Goban Spur) and two transects across the Iberian Margin with steep slopes and close to the shore. The northern Galician transect (off La Coruña) was situated in an area subjected to wind-induced upwelling events. The western Galician transect was also subjected to upwelling, was additionally influenced by outflows of water rich in organic matter from the Rías Bajas. This transect also included the Galicia Bank. Macrofauna density decreased exponentially from the shelf edge (154 m) to the abyssal plain (4951 m) and different communities occurred on the shelf, the upper- and lower slope and on the abyssal plain. Apart from two extremely low-density stations on the Iberian Margin, there were no significant differences in the meiofauna between the Goban Spur and the Iberian Margin. Along the La Coruña-transect a station where meiofaunal densities were low occurred at a depth of 1522 m, where the sediment was characterised by having a high median-grain size, ripple structures, a low Corg and total N content. There were relatively high numbers of macrofaunal filter-feeders but low numbers of crustaceans, indicating a high current velocity regime. On top of the Galicia Bank (˜770 m) the sediment consisted mainly of shells of pelagic foraminifers, and had low contents of Corg and N. The macrofauna was dominated by filter-feeding and carnivorous taxa. At both these stations meiofauna densities were low. Meiofauna densities and community structure differed between the Goban Spur and the Iberian Margin. Meiofauna densities on the Galician shelf were more than double those on the Goban Spur shelf. The two deep stations on the La Coruña transect and the deepest station on the Galicia Bank transect all contained meiofaunal densities that were higher than found at similar depths off the Goban Spur. The meiofaunal densities were inversely correlated with %CaCO3 content and, excluding the shelf stations, were positively correlated with both %Corg and total N at the Iberian Margin. Neither upwelling nor the enriched outflows from the rias affected the macrofauna, but meiofaunal densities were greatly enhanced. 相似文献
3.
《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(3):811-832
Total hydrolysable amino acids (THAA), individual amino acid distributions, total organic carbon (TOC) and total nitrogen (TN) were measured in sediments across the Goban Spur continental slope at water depths of 651, 1296 and 3650 m. Objectives were to examine (1) differences in organic matter (OM) degradation state in surface sediments across the slope from sedimentary amino acid compositions, and (2) whether these differences are related to particle size distributions. Application of a ‘reaction–diffusion’ model to the sediment concentration profiles showed that TOC and THAA degradation rate constants decreased with increasing water depth. Ratios of degradation rate constants of THAA over TOC indicated that THAA turn over faster than TOC at 651 and 1296 m water depth only. From estimates of degradation rate constants of individual amino acids, it was concluded that with increasing water depth fewer amino acids contribute to overall THAA degradation. The contribution of THAA to TOC mineralisation decreased from the upper to the lower slope. Since at all three sampling stations the amino acids with the highest relative contribution to THAA had a higher abundance in sediments with reduced THAA mineralisation rates, we conclude that the overall amino acid reactivity decreases with increasing water column depth. A principal component analyses, carried out on normalised amino acid mole percentages, established significant shifts in amino acid compositions and confirmed that (1) OM degradation state increased from 651 to 3650 m and (2) that OM in the finest fraction at the shallowest station appeared to be considerably less degraded than in the coarser fractions or any size fractions at the deeper stations. Therefore, we conclude that downslope transport, sorting and accumulation of fine particles with continuous mineralisation of OM attached to the particles during vertical and lateral transport results in an increasing organic matter degradation state from the upper slope to the abyssal plain. 相似文献
4.
The Meriadzek Terrace forms part of the continental margin in the Bay of Biscay at a depth between that of the Continental shelf and the abyssal plain. Reflection profiles show that it is bounded on either side by basement ridges with a sediment infill between the ridges. It was probably formed by downfaulting of the continental shelf, possibly connected with the opening of the Bay of Biscay. 相似文献
5.
Near bottom water samples and sediments were taken during five cruises to 6 stations forming a transect across the N.W. European Continental Margin at Goban Spur. Flow velocity spot measurements in the benthic boundary layer (BBL) always increased from the shelf to the upper slope (1470 m) from 5 to 9 cm s−1 in spring/summer and from 15 to 37 cm s−1 in autumn/winter. Decreasing values were detected at the lower slope (2000 m) and the lowest values of ca. 2 cm s−1 at the continental rise at 4500 m water depth. Long term measurements with a benthic lander at 1470 m show that currents have a tidal component and reach maximum velocities up to 20 cm s−1, sufficiently high periodically to resuspend and transport phytodetritus. During these long-term observations, currents were always weaker in spring/summer than in autumn/winter. Critical shear velocities of shelf/slope sediments increased with depth from 0.5 to 1.7 cm s−1 and major resuspension events and Intermediate Nepheloid Layers (INLs) should occur around 1000 m. Chloroplastic Pigment Equivalents (CPE) ranged from 0.0 to 0.21 μg dm−3, Particulate Organic Carbon (POC) from 12 to 141 μg dm−3 and Total Particulate Matter (TPM) from 0.2 to 10.0 mg dm−3. Aggregates in the BBL occurred with a median diameter of 152 to 468 μm. Data on suspended particulate matter in the near-bottom waters showed that hydrodynamic sorting within the particulate organic fraction occurred. Phytodetritus was packaged in relatively large aggregates and contributed little to the total organic carbon pool in nearbottom waters (CPE/POC ca.0.2%). The main organic fraction has low settling velocities and high residence times within the benthic boundary layer. As POC was not concentrated in the near bed region the degree to which carbon is accessible to the benthic community depends on aggregate formation, subsequent settling and/or biodeposition of the POC. Close to the sea bed downslope transport may dominate. Under flow conditions high enough to resuspend fresh phythodetritus from sediments at the productive shelf edge, this could be transported to 1500 m (Goban Spur) or abyssal depth (Canyon site between Meriadzek and Goban Spur) within 21 days. 相似文献
6.
The rate of benthic denitrification in slope and rise sediments of a transect across the N.W. European Continental Margin (Goban Spur) was evaluated from 31 pore water nitrate profiles obtained during six cruises between May and October. All profiles had well separated zones of nitrification and denitrification. High near-surface nitrate concentrations prevented the influx of nitrate from the bottom water. The denitrification rates obtained from steady-state-modelling ranged from 0.13 to 2.56 μmol N cm−2 y−1 and showed an exponential increase both with decreasing water depth and with increasing rate of organic carbon degradation. Denitrification rates in a nearby canyon, which did not follow these relationships, were estimated to be much higher as a result of erosion and redistribution of organic matter. Denitrification at the Goban Spur slope and rise is much lower than previously reported for similar environments in the Pacific resulting predominantly from the different oxygen and nitrate concentrations in the bottom water. A weighted average for the whole slope and rise sediment system shows that 17% of the particulate organic nitrogen input (8.93 μmol N cm−2 y−1) is denitrified and only 1% is buried, the rest being released as nitrate. Although being ten times higher compared with basin sediments, denitrification on the slope and rise is several times lower than on the adjacent shelf. 相似文献
7.
《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(9):1565-1591
A simple model with horizontal and vertical diffusivities and settling velocity is used to calculate expected distributions of suspended particulate matter in a section across the continental shelf and slope. Dependencies on the shelf and slope profile, diffusivities, settling velocity, cross-slope advection and boundary sources/sinks are explored. It is found that the strongest factors are relative values of diffusivities and settling velocity, and the distribution of sources and sinks – including bottom deposition or resuspension. The latter is the principal means whereby an increased concentration near the bottom is likely, and is suggested as the usual reason for increased deposition recorded by sediment traps nearer the bottom. Observed thin, near-horizontal intermediate nepheloid layers put bounds on the vertical diffusivity and settling velocity, e.g. O(10-4 m2 s-1, 10-5 m s-1) over Goban Spur in OMEX. 相似文献
8.
《Progress in Oceanography》2002,52(2-4):171-194
As a contribution to ocean-shelf exchange studies, the Sediment Transport and Boundary Layer Equipment STABLE has been deployed west of Spain near 42°40’N in 200m water depth, in December and August, and at three other continental shelf edge and slope locations off north-west Europe. Turbulence at 8Hz and acoustic back-scatter at 4Hz were measured at three levels between 0.3 and 1 m above the bed.Typically the speed profile shows little shear; the turbulence data are necessary to estimate near-bed stress. Reynolds stress and total turbulence energy approaches give consistent results; total turbulence results appear more robust but can be affected by long surface waves. Typical peak values of friction velocity u1 per tide were 10 mm/s off Spain and 7–18 mm/s at the other locations, and they were asymmetric owing to along-slope flow. Record maxima were 30 mm/s, 11–48 mm/s respectively, sufficient to move local sediment except for a short ‘event-free’ record at Goban Spur. Acoustic backscatter (SPM) showed peaks matching peaks of u1 or waves in the case of winter deployments off Scotland and Spain.Comparison of these STABLE measurement periods with contemporary current records of longer duration suggests that bed stresses in all these upper-slope locations are often sufficient to move the local sediment. Off Spain, shelf sediments are re-suspended and transported down-current. The sandy fraction settles soon, but the fine fraction (wS < 0.1 mm/s) is progressively winnowed down-current to the shelf edge, suggesting export of the bound organic matter. 相似文献
9.
《Marine Geology》2001,172(3-4):265-285
Studies of latest Quaternary continental slope sediments at two localities on the east Australian margin have revealed markedly different responses to late Quaternary sea level fluctuations. Offshore of Noosa, in the sub-tropics, the sediment is predominantly a mixture of fine metastable carbonate, siliciclastic material, and pelagic carbonate. Important features of the stratigraphy include a siliciclastic-dominated facies deposited relatively slowly during the last glacial lowstand (sedimentation rate ≤8 cm/ka), and a calcareous facies, rich in metastable carbonate, deposited more rapidly during the late post-glacial transgression (sedimentation rates 15–24 cm/ka). Highstand and transgressive sedimentation rates are greater than lowstand rates by a factor of 2.5–6 due to increased shelf carbonate productivity after flooding of the mid-shelf. Off Sydney, in temperate latitudes, continental slope sediment is largely a mixture of fine siliciclastic material and pelagic carbonate. Mean sedimentation rates range from 2 to 5 cm/ka over the last four oxygen isotope stages, with mean glacial/interstadial rates higher than Holocene rates by a factor of ∼1.36. This largely reflects the transfer of siliciclastic mud from the shelf to the slope during sea level regression. In both localities, facies changes on the slope are not related to specific sea level states (e.g. lowstand facies, transgressive facies, etc.), but reflect instead the interaction of changing sea level with shelf morphology. 相似文献
10.
The Meriadzek Terrace (a 2100m deep plateau on the North-East Atlantic continental slope) was chosen as the experimental site for a multidisciplinary programme to observe the parameters needed for a better understanding of biological processes in the benthic environment.Two approaches were used to study the input of particulate matter to the bathyal seabed: sediment traps and indirect particle concentration measurements with nephelometry. These two technologies do not measure particles of the same size range, but as we are interested in the fluctuations of the particle supply, their results are complementary.Vertical profiles of nephelometry show that over the Meriadzek Terrace there is 125m thick nepheloid layer immediately above the bottom.The dynamics in the deep layer has been determined by measurements made with a Module Autonome Pluridisciplinaire (MAP), an in situ monitoring device developed at IFREMER which measures currents, nephelometry, temperature vertical profile near the bottom.Throughout six months of measurements in 1984, the currents at 0.5m and 120m above the bottom were subject to semi-diurnal tidal oscillations. The intensity of light scattering recorded with the nephelometer on the MAP was highly correlated with current velocities especially with semidiurnal tidal oscillations which seem to induce local resuspension. There are also longer term fluctuations, notably a very strong event which lasted several days during August. This event lagged behind a period of high intensity of internal waves correlated with a reversal in current direction. The sediment trap (Pièges à Particules “PAP”) observations showed that the particle fluxes on the Meriadzek Terrace have a cycle of variation similar to primary production which is characterized by a maximum in May during the phytoplankton bloom and a minimum during January. There was also interannual fluctuation.These two kinds of results point out the different time scales (from some hours to several months) of the large temporal fluctuations which affect the near-bottom particle behaviour. 相似文献
11.
选择物质来源相对单一、区域较广的浙江沿岸东海内陆架区，以4种主要粘土矿物(伊利石、蒙皂石、高岭石、绿泥石)为研究对象，以探讨长江粘土矿物作为示踪标记的稳定性问题。研究区5组沉积物样品中粘土矿物的X射线衍射实验及含量分析结果表明，伊利石、蒙皂石和高岭石的相对含量较稳定，具有作为长江物源示踪标记的价值．而各区域的绿泥石含量之间不具有显著的统计相似性。现有资料还不能完全解释长江口及邻近东海内陆架区内粘土矿物组合的相对稳定状态，今后应对絮凝作用、沉积分异作用、海底生物地球化学作用等因素的效府做进一步的研究。 相似文献
12.
应用X射线衍射(XRD)方法对南海北部西侧海域315个表层沉积物<2μm的粘土组分进行分析.结果表明,本研究区粘土矿物有伊利石、绿泥石、蒙脱石和高岭石,其组合特征在不同区域表现出明显的差异.根据粘土矿物的空间分布特征以及研究区的海底地形特征,研究区大致可以分为3个不同区块:A区是珠江口外的大陆架区域;B区是海南岛以东陆架陆坡区域;C区为西沙海槽至西沙群岛附近区域.根据研究区表层粘土矿物分布特征、周围河流供给的主要粘土成分以及洋流搬运作用,发现A区高岭石(平均含量为19%)主要来自珠江,伊利石与绿泥石(平均含量分别为53%和18%)主要由台湾的河流提供,有珠江物质的混合,蒙脱石含量较低(平均含量为10%).B区的高岭石(平均含量为13%)主要由海南岛的河流提供,蒙脱石(平均含量为16%)主要由吕宋岛的河流提供,B区东部的伊利石和绿泥石来自台湾的河流,B区西部伊利石和绿泥石主要来自红河、越南中部河流,海南岛物源亦有贡献.C区高岭石含量较低(平均含量为12%),越南中部河流和红河为C区蒙脱石(平均含量为14%)的主要物源区,C区东部伊利石和绿泥石来自台湾的河流,C区西部伊利石和绿泥石主要来自红河、越南中部河流. 相似文献
13.
黏土矿物研究在示踪物源、源区风化历史乃至洋流变迁能力等方面具有重要的作用,尽管目前对南海表层沉积物黏土矿物宏观分布特征已获得了较系统的认识,但在受珠江和海南岛物源共同影响的南海西北部其高分辨率的黏土矿物学工作还未开展。本文对南海西北部表层沉积物中的黏土矿物组成、结晶学特征进行了分析,讨论了研究区黏土矿物的物质来源。结果表明,南海西北部表层沉积物的黏土矿物组成以伊利石为主（平均45%）,蒙脱石（平均27%）与高岭石（平均21%）次之,绿泥石含量最少（平均6%）。在区域空间分布上,蒙脱石含量呈现西南高东北低的特征,伊利石含量则与之相反;高岭石含量表现为近岸高离岸低,而绿泥石含量呈现离岸高近岸低的特征。总体上,研究区表层沉积物黏土矿物组成与现代珠江沉积物组成差异较大,而与珠江口2.5 ka前的沉积物黏土矿物组成比较接近,并且结合研究区岩心揭露的全新世以来极低的沉积速率（4 cm/ka）以及上部很薄（小于0.6 m）的泥质沉积,推测该区表层沉积物可能并非是现代沉积的结果,更可能主要来自全新世末期古珠江输送的沉积物。除古珠江作为研究区表层沉积物中蒙脱石的一个主要来源外,海南岛北部河流也贡献了少量蒙脱石到其邻近的东南海域。运用高岭石/伊利石比值和伊利石化学指数等进一步对比分析表明,珠江是研究区沉积物中伊利石、高岭石和绿泥石的主要物源,其次台湾和海南岛也可能分别提供了少量富含伊利石/绿泥石和高岭石的沉积物。本工作对于南海西北部沉积物源-汇过程和相应的古环境研究有重要的参考意义。 相似文献
14.
通过研究南沙群岛西南海区44个站表层碳酸盐沉积特征,综合分析了沉积物类型、碳酸盐的生物组成、矿物成分、地球化学等,根据碳酸盐沉积的岩性参数之间的关系及相应的沉积环境,应用主成分分析统计对比,提出该海区碳酸盐沉积的六个沉积相及其特征:大陆坡半深海-深海相,南部中、外大陆架浅海相,西部中、外大陆架浅海相,南部内大陆架浅海相,礁体相,礁体过渡相。 相似文献
15.
A. Oliveira F. Rocha A. Rodrigues J. Jouanneau A. Dias O. Weber C. Gomes 《Progress in Oceanography》2002,52(2-4)
The Northern Iberian margin is a typical example of a continental margin subjected to seasonal highly energetic regime (waves and tides) and receiving inputs of continental sediments via riverine discharges. The principal goal of this study has been to use clay minerals as indicators of sedimentary dynamics in the open shelf system. The distributions of clay mineral in the top layer of the sedimentary cover are shown to be related to their continental sources, but also reflect the influences of winter storms and longshore currents in determining the pathways of sediment transport.The mineralogical composition of the material issuing from the rivers is very similar to the general mineralogical composition of the fine fractions of the seabed sediments. Those deposits that are directly influenced by riverine discharges have higher contents of kaolinite (>20%), whereas those that are not have higher contents of illite (>80%). The available data indicate no significant quantities of terrigenous particles are being discharged from the Spanish rias. Therefore, we conclude that physical processes are controlling the clay mineral distributions and that, despite contributions from the Minho River, the main source of fine detrital particles to the shelf region is the Douro River discharge. These particles settle on the middle shelf, below the 60 m isobath. During storm events these particles are re-suspended and advected northwards to the Galician shelf or into deeper domains. Thus the distributions of the clays indicate there is a net transport of fine sediments both northwards and off-shelf. 相似文献
16.
Natural oil and gas seeps on the Black Sea floor 总被引：3，自引：0，他引：3
Migration of hydrocarbons to the seafloor in the Black Sea occurs via direct seepages, mud volcanoes, and development of fluidized sediment flows (e.g., diapers). Gas migration occurs on the shelf, continental slope, and abyssal plain. Gas hydrates are spatially related to gas accumulations and are present in shallow subsurface sediment layers. Their distribution is controlled by the activity of mud volcanoes. In regions of methane seepages, specific biogeochemical processes related to the activity of methane-oxidizing bacteria are evident. This activity results in the formation of diagenetic minerals (carbonates, sulfides, sulfates, phosphates and other minerals). 相似文献
17.
The riverine mud that escapes retention in the estuaries and enters the Gulf of Papua appears to be transported southeastward, across depth contours, by the prevailing currents in a series of wind-driven events. The mud deposits to the southeast of the rivers, at the mid-shelf region within a depth range of 40–60 m. Mud transported farther eastward is carried down the continental rise. Coarser riverine sediment (silt and sand) is deposited closer inshore. On the outer shelf (depth >60 m) relict carbonate debris dominates. The area of mud has maximum rates of pelagic and benthic productivity in the gulf. 相似文献
18.
Detailed sedimentological, geochemical and isotopic analyses were carried out on sediment samples from ODP Site 720A on the
Indus Fan, Arabian Sea. High values of calcium carbonate associated with low values of Al and Ti from 0 to 375 ka, and low
values of calcium carbonate along with high values of Al and Ti from 375 to 525 ka represent two distinct sedimentary sequences.
The sediments deposited from 525 to 375 ka correspond to a turbidite sequence, characterized by a high terrigenous input of
coarse-grained sediments composed mostly of sand and silt. The sediments deposited from 375 ka to the present day comprise
a pelagic sequence, consisting of pelagic material and clay. The major turbidity flow between 375 and 525 ka resulted in the
greatest development of the Indus Fan during the late Quaternary. Most of the active channels were buried by 375 ka, followed
by deposition of mainly pelagic sequences since then. Enrichment of an Indus-derived Himalayan clay mineral assemblage (illite
and chlorite) in both the turbiditic and pelagic sequences reveals that the source and supply of clay minerals to the Indus
Fan were the same during pre- and post-turbidite deposition. At ODP Site 720A, Al, Ti and terrigenous material do not show
any systematic changes with respect to glacial and interglacial periods, suggesting that sea-level changes are not directly
responsible for the terrigenous material supply to this site. Rather, a major switch in distributary channels away from the
western margin of the Indus Fan is suggested. 相似文献
19.
Current velocity and suspended sediment concentration measurements at anchor stations in the downstream extremity of the Gironde estuary indicate that during periods of high river discharge, a significant amount of suspended sediment is transported out of the estuary onto the adjacent continental shelf. The vertical profile of the residual (non-tidal) suspended sediment flux is similar to that of the residual current velocity, with a net upstream flux near the bottom and an overlying seaward-directed transport. The overall, depth-integrated result is a net seaward transport of suspended sediment out of the estuary. It appears that this net seaward transport varies directly with tidal amplitude.Aerial photography and water sampling indicate that during high river inflow, the downstream extremity of the turbidity maximum extends onto the continental shelf at ebb tide. The tidal and coastal current patterns of the inlet and inner shelf induce a northward transport of the turbid estuarine water, and at each tidal cycle, a certain amount of suspended sediment leaves the estuary; part of this sediment is deposited in a silt and clay zone on the continental shelf. 相似文献
20.
For the first time, an element abundance table of China Shelf Sea sediments is published based on 286 samples from the continental shelf of China analyzed for 62 chemical elements. The shelf sediments result from the redistribution of sediments from China over the continental shelf. On the basis of comparison of element abundances among the China shelf samples, hemipelagic Okinawa Trough samples, and pelagic brown clay from the West Pacific, it is clear that each has its own elemental characteristics. Hg anomaly enrichment in Okinawa Trough sediments may be used as an indicator of hydrothermal activity. 相似文献