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1.
Rates of sediment accumulation and biological particle mixing in eight cores from the Peru shelf have been estimated by application of uranium-series disequilibrium techniques and radiocarbon dating. Activities of 210Pb, 226Ra, 234Th and 238U have been determined in closely spaced intervals in each sediment core. Biological particle mixing coefficients were determined via a two-box advection-diffusion steady-state mixing model based on the distribution profiles of excess 210Pb and, in some cases, excess 234Th activities. The sedimentation rates estimated were in the order of a few millimeters/yr except for cores enriched in phosphatic components which displayed rates a few orders of magnitude slower. Bioturbation was significant in most cores studied with the exception of one core collected from within the middle of the oxygen-minimum zone. Estimated biological mixing coefficients were in the order of 100–101 cm2 yr−1 for the surface mixed layer and 10−1–100 cm2 yr−1 for the layer below. Sediment slumping appears to have affected the 210Pb distribution of two or three of our cores. 相似文献
2.
TOPEX and Jason were the first two dual-frequency altimeters in space, with both operating at K u- and C-band. Thus, each gives two measurements of the normalized backscatter, σ 0, (from which wind speed is calculated) and two estimates of wave height. Departures from a well-defined relationship between the K u- and C-band σ 0 values give an indication of rain. This study investigates differences between the two instruments using data from Jason's verification phase. Jason's K u-band estimates of wave height are ∼1.8% less than TOPEX's, whereas its σ 0 values are higher. When these effects have been removed the root mean square (rms) mismatch between TOPEX and Jason's K u-band observations is close to that for TOPEX's observations at its two frequencies, and the changes in σ 0 with varying wave height conditions are the same for the two altimeters. Rain flagging and quantitative estimates of rain rate are both based on the atmospheric attenuation derived from the σ 0 measurements at the two frequencies. The attenuation estimates of TOPEX and Jason agree very well, and a threshold of-0.5 dB is effective at removing the majority of spurious data records from the Jason GDRs. In the high σ 0 regime, anomalous data can be caused by processes other than rain. Consequently, for these low wind conditions, neither can reliable rain detection be based on altimetry alone, nor can a generic rain flag be expected to remove all suspect data. 相似文献
3.
在独流减河入海口附近河道之间的盐沼采用人工探坑侧壁连续取样,获得2个站位的沉积物样品。通过 210Pb和 137Cs定年法建立年代框架,结合粒度分析、有孔虫鉴定和水文数据,探讨了该区的现代洪水事件沉积。结果表明,该区沉积物的 210Pb exc比活度-深度剖面中存在2处明显的低值沉积层,分别在3~6 cm和10~14 cm深度,这2个沉积层分别对应 137Cs曲线的次峰和主峰。这两层与上下相邻层位相比呈现粒径较粗、分选较差,有孔虫丰度较低、破损百分比较高的特征。 210Pb测年结果显示, 137Cs曲线下部的主峰对应的年龄为1963年,与全球性的最大峰值形成时间相对应,而上部的次峰对应的并非1986年切尔诺贝利核泄漏事故形成的次峰。区内水文数据显示,在1963和1996年分别发生了2次较大的洪水事件。因此,推断S4和S5站位剖面中2个特殊的沉积层是由洪水事件造成的。本研究说明高分辨率沉积特征的多指标研究可以较为准确地揭示洪水等灾害性事件发生的年代和频率,这有利于系统地揭露海陆过渡带地区地质历史时期灾害和气候事件的频率和强度,为灾害预防和未来规划提供科学依据。 相似文献
4.
A study of the East Frisian Islands has shown that the plan form of these islands can be explained by processes of inlet sediment bypassing. This island chain is located on a high wave energy, high tide range shoreline where the average deep-water significant wave height exceeds 1.0 m and the spring tidal range varies from 2.7 m at Juist to 2.9 m at Wangerooge. An abundant sediment supply and a strong eastward component of wave power (4.4 × 10 3 W m −1) have caused a persistent eastward growth of the barrier islands. The eastward extension of the barriers has been accommodated more by inlet narrowing, than by inlet migration. It is estimated from morphological evidence that a minimum of 2.7 × 105 m3 of sand is delivered to the inlets each year via the easterly longshore transport system. Much of this sand ultimately bypasses the inlets in the form of large, migrating swash bars. The location where the swash bars attach to the beach is controlled by the amount of overlap of the ebb-tidal delta along the downdrift inlet shoreline. The configuration of the ebbtidal delta, in turn, is a function of inlet size and position of the main ebb channel. The swash bar welding process has caused preferential beach nourishment and historical shoreline progradation. Along the East Frisian Islands this process has produced barrier islands with humpbacked, bulbous updrift and bulbous downdrift shapes. The model of barrier island development presented in this paper not only explains well the configuration of the German barriers but also the morphology of barriers along many other mixed energy coasts. 相似文献
5.
文章利用观测和模式数据, 并基于混合层盐度收支方法, 研究了热带东太平洋淡水池的季节变化。研究发现: 热带东太平洋淡水池具有显著的季节变化, 由海表强迫(蒸发与降水)、水平平流和次表层过程共同控制。淡水池的季节变化主要分为扩张与收缩两个阶段。4月至11月为扩张阶段, 淡水池向西扩张, 最大体积和面积比最小时扩大将近一倍, 分别达到2.83×10 5km 3和8.94×10 6km 2。热带辐合带向北移动带来的强降水是淡水池扩张的主要原因, 海表强迫决定了混合层盐度降低。12月至3月为淡水池收缩阶段, 海表淡水通量的减弱、水平平流和次表层过程的增强导致混合层盐度升高, 淡水池向东收缩。 相似文献
6.
In order to reconstruct former sea level we have developed a foraminifera-based transfer function using three models based on a modern dataset of 59 samples and 23 species obtained from four Basque marshes in Northern Spain. The relationship between observed and foraminifera-predicted elevation illustrated the strong performance of the transfer function ( r2jack ranges from 0.74 to 0.81). These results indicated that precise reconstructions of former sea levels are possible (error ranges from 0.11 to 0.19 m). The transfer function was used to calibrate the foraminiferal assemblages collected from a 50 cm salt marsh core. We placed the foraminifera-based reconstructions into a temporal framework using 137Cs, Pb concentrations, and 210Pb-derived sediment accumulation rates. The resulting relative sea-level curve is in good agreement with regional tide-gauge data. Both instrumental data and microfossil records suggest a rate of relative sea-level rise of approximately 2 mm yr − 1 for the 20th century. 相似文献
7.
Distinctive light–dark color cycles in sediment beneath the Benguela Current Upwelling System indicate repetitive alternations in sediment delivery and deposition. Geochemical proxies for paleoproductivity and for depositional conditions were employed to investigate the paleoceanographic processes involved in creating these cycles in three mid-Pleistocene intervals from ODP Sites 1082 and 1084. Concentrations of total organic carbon (TOC) vary between 3.5 and 17.1%. Concentrations of CaCO 3 vary inversely to TOC and Al, which suggests that both carbonate dissolution and terrigenous dilution contribute to the light–dark cycles. Opal concentrations are independent of both TOC and CaCO 3, therefore eliminating diatom production and lateral transport of shelf material as causes of the light–dark cycles. δ 13C org and δ 15N tot values do not vary across light–dark sediment intervals, implying that the extent of relative nutrient utilization did not change. The stable δ 15N tot values represent a balanced change in nitrate supply and export production and therefore indicate that productivity was elevated during deposition of the TOC-rich layers. Parallel changes in concentrations of indicator trace elements and TOC imply that changes in organic matter delivery influenced geochemical processes on the seafloor by controlling consumption of pore water oxygen. Cu, Ni, and Zn are enriched in the darker sediment as a consequence of greater organic matter delivery. Redox-sensitive metals vary due to loss (Mn and Ba) or enrichment (Mo) under reducing conditions created by TOC oxidation. Organic matter delivery impacts subsequent geochemical changes such as carbonate dissolution, sulfate reduction and the concentration of metals. Thus, export production is considered ultimately responsible for the generation of the color cycles. 相似文献
8.
The velocity profiles under crest of a total of 62 different steep wave events in deep water are measured in laboratory using particle image velocimetry. The waves take place in the leading unsteady part of a wave train, focusing wave fields and random wave series. Complementary fully nonlinear theoretical/numerical wave computations are performed. The experimental velocities have been put on a nondimensional form in the following way: from the wave record (at a fixed point) the (local) trough-to-trough period, TTT and the maximal elevation above mean water level, η m of an individual steep wave event are identified. The local wavenumber, k and an estimate of the wave slope, ε are evaluated from ω 2/( gk)=1+ε 2,
where ω=2π/ TTT and g denotes the acceleration of gravity. A reference fluid velocity,
is then defined. Deep water waves with a fluid velocity up to 75% of the estimated wave speed are measured. The corresponding kη m is 0.62. A strong collapse of the nondimensional experimental velocity profiles is found. This is also true with the fully nonlinear computations of transient waves. There is excellent agreement between the present measurements and previously published Laser Doppler Anemometry data. A surprising result, obtained by comparison, is that the nondimensional experimental velocities fit with the exponential profile, i.e. e ky, y the vertical coordinate, with y=0 in the mean water level. 相似文献
9.
沉积物插管短柱样品于2013年4月采自大连湾2010年“7·16”溢油事故污染区,BQ050站与BQ007站分别位于生物分散剂和化学分散剂喷洒区。沉积物的可溶有机质含量(沥青A)、有机碳同位素组成(δ 13C org)和 210Pb比活度分析结果表明:喷洒生物分散剂的重污染区(BQ050站),沉积物中TOC含量为0.58%～1.51%,平均为1.15%;δ 13C org值为-22.2‰～-20.5‰PDB,平均为-21.74‰PDB;沥青A含量为0.061 5%～0.566 4%,平均为0.174 9%;沥青A/TOC比值为7.0%～34.8%,平均为14.13%; 210Pb ex比活度存在异常峰值分布,垂向分布特征与沥青A相似;2～16 cm段沉积物的可溶有机质具有明显的外来输入特征。喷洒化学分散剂的较轻污染区(BQ007站),沉积物中TOC含量为0.61%～1.14%,平均为0.87%,除8～14 cm层段外,比BQ050站略低;但沥青A含量与沥青A/TOC比值明显低于前者;δ 13C org值较BQ050站轻; 210Pb ex比活度随柱样深度呈指数衰减,对数相关;外来有机质输入量较低。截至2013年4月,BQ050站溢油污染物在海底下16 cm深度处有特征信号,溢油污染物沥青A 组分垂向迁移距离约为15 cm。 相似文献
10.
为了探究北部湾养殖区域香港牡蛎( Crassostrea hongkongensis)体内的异养细菌和弧菌数量及其耐药概况变化, 对不同养殖场牡蛎体内的异养细菌进行分离培养, 并统计其数量, 通过药敏纸片扩散等方法研究了细菌的耐药状况。结果显示: 牡蛎在高死亡率养殖环境中体内的异养细菌[(8.6±0.4)×10 6CFU·g -1]和弧菌[(9.5±0.4)×10 5CFU·g -1]数量较高, 在中死亡率环境中体内的异养细菌[(6.9±0.2)×10 6CFU·g -1]和弧菌[(4.5±0.6)×10 5CFU·g -1]数量次之, 在低死亡率养殖环境中体内的异养细菌[(3.3±0.1)×10 6CFU·g -1]和弧菌[(2.5±0.6)×10 5CFU·g -1]数量最低。耐药细菌主要为革兰氏阴性菌, 对β-内酰胺类(青霉素)、糖肽类(万古霉素)的耐药率较高, 对四环素类(四环素、多西环素)的耐药率次之, 对氨基糖苷类(链霉素、庆大霉素、妥布霉素、新霉素)、大环内酯类(红霉素)、喹诺酮类(诺氟沙星、环丙沙星、氧氟沙星、恩诺沙星)的耐药率较低。在高死亡率环境中牡蛎体内的多重耐药菌占79.7%, 其耐药谱型(48种)较广; 在中度死亡率环境中牡蛎体内的多重耐药菌占66.2%, 其耐药谱型为30种; 在低死亡率环境中牡蛎体内的多重耐药菌占58.4%, 其耐药谱型为17种。本文探究了牡蛎死亡率与其体内异养细菌数量和细菌耐药性的关系, 结果显示牡蛎在高死亡率环境中体内的耐药细菌数量多、耐药谱型较广, 低死亡率环境中牡蛎体内的耐药细菌数量较少, 异养细菌数量与牡蛎死亡率呈正相关关系, 两者相关系数为0.996。 相似文献
11.
New light-stable carbonate-carbon isotope and lattice-bound CO 2 data from Quaternary Peru-Chile margin phosphatic nodules, crusts and pelletal grains, and from associated dolomicritic concretions, are presented, which provide constraints on the timing and mechanisms of growth of these phases in organic carbon-rich sediments. Comparison of δ 13C values from carbonate fluorapatite (CFA) nodules and pelletal grains (−4.8 to 0.0‰ and −2.9 to +1.0‰ PDB, respectively) with pore-water total dissolved δ 13C values from these sediments suggests early authigenic CFA precipitation from pore waters within a few centimeters of the sediment-water interface in association with suboxic to perhaps anoxic microbial degradation of organic matter. In contrast, the dolomicritic cores of nodules recovered from about 12°S display both strongly negative to positive δ 13C values (−10.8 to +6.1‰) characteristic of formation deeper in the sediments in association with methanogenic and perhaps sulfate reduction microbial processes. The amount of structural carbonate in CFA suggests that carbonate substitution generally increases as δ13C in CFA decreases, a probable consequence of increasing carbonate and accompanying charge-balancing substitutions in the CFA lattice in response to increasing pore-water carbonate ion concentrations with depth below the sediment-water interface. In one buried upward-growing nodule, decreasing CFA δ13C and increasing structural CO2 also correspond to decreasing CFA growth rates. These data suggest that in addition to other constraints such as pore-water phosphorus and fluoride availability, the lower limit of CFA precipitation in suboxic to anoxic sediments may be controlled by lattice poisoning due to excessive dissolved carbonate ion concentrations. In organic-rich Peru-Chile margin sediments this depth threshold appears to be at approximately 5–10 cm below the sediment-water interface where maximum CFA CO2 contents of about 6 Wt.% occur; in less organic-rich settings, greater depths of precipitation of CFA may be anticipated. Below this relatively shallow depth of CFA precipitation on the Peru shelf, high pore-water alkalinity and associated elevated total dissolved carbon and carbonate ion concentration apparently favor the precipitation of authigenic carbonates. 相似文献
12.
风尘通过影响大气辐射平衡和海洋生态系统的营养物质供应从而调控全球气候,是国际学术界广泛关注的热点问题之一。近年来,风尘的相关研究取得一系列重要进展,并提出将 232Th作为一种准确重建约50万年以来风尘沉积通量的途径。本文首先介绍基于 230Th的标准化方法,它可用于修正由于海洋底流频繁扰动引起的沉积物沉积速率变化,然后结合 230Th标准化方法修正后的232Th通量,并利用10.5μg/g换算得出的风尘沉积通量,通过和实测值对比,阐明了此方法的准确性。进一步通过对比晚全新世与末次冰盛期 230Th标准化后的基于 232Th获取的风尘沉积通量,也验证了此方法的可靠性。通过总结该方法在西太平洋的前期应用,认为此方法在西太平洋有着广阔的应用前景。 相似文献
13.
Carbon and oxygen isotope ratios of 59 samples of Mesozoic ophicalcites from the north-central Apennines were measured. Strontium content and isotope ratios were only determined for selected samples. The data obtained (−4.1 ≤ δ 13C ≤ + 3.0; 16.5 ≤ δ 18O ≤ 30.1; 0.7076 ≤ 87Sr/86Sr ≤ 0.7086; 60 ≤ Sr ppm ≤ 1140) suggest that the carbonate cement of the Apennines ophicalcites had a marine origin. The 18O/16O values of most of the carbonates studied, however, indicate that the rocks have interacted with hydrothermal fluids, dominantly represented by sea water. In particular, the rocks from the northern section of the Apennines apparently reequilibrated their δ 18O content at higher temperature than those from the central zone. Strontium isotope ratios, close to the Cretaceous—Cenozoic ocean water values, are well in agreement with such a kind of sea water/ophicalcites interaction, even if the carbonate cement formed earlier during the Jurassic period. 相似文献
14.
Two cores from the Bannock Basin in the eastern Mediterranean have been analysed for δ 180 and the δ 13C in planktonic foraminifera. One core (02-PC) was extracted from the anoxic brine, the other (08-GC) from a plateau east of the brine. The absence of sapropelic muds in Core 08-GC from the two Holsteinian euxinic cycles, together with the presence of isotopic spikes, suggests that the plateau has risen during the last ca. 200,000 years by ca. 2.5 mm/yr. The δ180 amplitude of Globigerinoides ruber in eastern Mediterranean cores is only ca. 0.5%. larger than for this species in North Atlantic cores. This suggests that the surface oxygen isotopic composition of both bodies of water followed each other fairly closely during the Late Pleistocene, except during the stagnant phases. 相似文献
15.
Fifty analyses of rare earth elements as well as mineralogical studies have been carried out on a suite of manganese nodules and crusts from the Central Indian Basin and the Western Indian Ocean. The aim was to identify the processes controlling the REE patterns of the phases hosting the REE in the manganese nodules, with an emphasis on an understanding of the Ce anomaly. This has involved separating the encrusting layers and nuclei physically as well as Fe-Mn oxides from the aluminosilicate phase chemically (using a 2 M HCl leach) prior to analysis. The presence of nodule nuclei seems to have little influence (mostly <5% to a maximum of 30%) on the overall magnitude of the Ce anomalies in these nodules. The ratios of concentrations of elements in the acid leachates and the corresponding bulk values yield flat REE patterns indicating that the aluminosilicate phase contributes very little to the Ce anomalies. Interelement relations indicate that the Ce anomalies are largely controlled by the amorphous mineral phase FeOOH.xH2O. The relationship of Fe, Ce anomaly and δ-MnO2 further suggests that Ce is chemisorbed onto iron oxyhydroxides which are epitaxially intergrown with δ-MnO2. The regional distribution of the Ce anomaly values appears to depend on many of the factors responsible for the uptake of other minor metals in nodules and crusts. 相似文献
16.
Organic carbon (OC) and nitrogen (N) contents and δ 13C and δ 15N values in total organic matter (OM) were measured in sub-surface sediments (0–30 cm sub-bottom) from 21 cores raised from the Laurentian Channel of the Gulf of St. Lawrence and the Labrador Sea, to document OM fluxes and storage along the eastern Canadian margin. Storage rates as high as 2.5 g m −2 yr −1 for OC and 0.2 g m −2 yr −1 for N are observed in the Laurentian Channel, suggesting that the shelf plays a significant role in terms of OM storage (from 1 to 2% of the primary production). Based on the isotopic composition of the essentially marine OM of the Labrador Sea (δ 13C/V-PDB=−21.9±0.4‰; δ 15N/AIR=7.6±0.6‰; n=12), there is no isotopic evidence for a significant relative input of terrestrial OM along the Laurentian Channel (δ 13C/V-PDB=−21.9±0.4‰; δ 15N/AIR=8.0±0.9‰; n=10), either due to high relative fluxes of marine OM and/or to the trapping of continental OM in the estuary and upstream. High storage rates of OM are also observed on the continental rise of the Labrador Sea (as high as 1.1 g C m −2 yr −1 and 0.09 g N m −2 yr −1). They contrast with one order of magnitude lower rates on the slope, due to low sedimentation rates (SR) and sediment winnowing by the Western Boundary Undercurrent (WBUC). Reduced early diagenetic alteration of OM is observed, particularly in the Laurentian Channel. It results in discrete (i) losses of OC and N, (ii) shifts in C/N ratios, suggesting preferential removal of N-bearing OM also highlighted by losses in total hydrolysable amino acids (HAA). In the Labrador Sea slope records, due to low SR, OM concentration changes linked to long term temporal variations may superimpose on these diagenetic trends, and some influence of the WBUC is noticeable. 相似文献
17.
It has recently been realized that the Arctic undergoes drastic changes, probably resulting from global change induced processes. This acts on the cycling of matter and on biogenic elements in the Arctic Ocean having feedback mechanisms with the global climate, for example by interacting with atmospheric trace gas concentration. A contemporary budget for biogenic elements as well as suspended matter for the Arctic Ocean as a baseline for comparison with effects of further global change is, thus, needed. Available budgets are based on the late Holocene sedimentary record and are therefore quiet different from the present which has already been affected by the intense anthropogenic activity of the last centuries. We calculated a contemporary suspended matter and organic carbon budget for the Kara Sea utilizing the numerous available data from the recent literature as well as our own data from Russian-German SIRRO (Siberian River Run-off) expeditions. For calculation of the budgets we used a multi-box model to simplify the Kara Sea shelf and estuary system: input was assumed to comprise riverine and eolian input as well as coastal erosion, output was assumed to consist of sedimentation and export to the Arctic Ocean. Exchange with the adjacent seas was considered in our budget, and primary production as well as recycling of organic material was taken into account. According to our calculations, about 18.5 × 106 t yr− 1 of sediments and 0.37 × 106 t yr− 1 of organic carbon are buried in the estuaries, whereas 20.9 × 106 t yr− 1 sediment and 0.31 × 106 t yr− 1 organic carbon are buried on the shelf. Most sources and sinks of our organic carbon budget of the Kara Sea are in the same order of magnitude, making it a region very sensitive to further changes. 相似文献
18.
混合过程是海洋中普遍存在的一种形式, 对气候变化、物质分布等起到了重要作用。地震海洋学是近十多年发展起来的一门新兴学科, 被广泛应用到物理海洋学问题的研究中, 具有高空间分辨率的突出优点。文章利用反射地震资料, 通过斜率谱方法, 分别获得了吕宋海峡以东黑潮区湍流段与内波段的耗散率及扩散率。结果显示, 在剖面深度200~800m的平均耗散率为10 -7.0W·kg -1, 平均扩散率为10 -3.3m 2·s -1, 比大洋统计均值10 -5.0m 2·s -1高约1~2个量级, 与前人在吕宋海峡的观测结果相一致。湍流段和内波段的扩散率空间分布差异较大: 湍流段扩散率高值区对应强流区域, 推测这里是中尺度涡边缘, 其次中尺度不稳定过程引起扰动增强, 进而引起湍流混合的加强; 内波段扩散率高值区出现在吕宋岛弧附近, 推测是内波遇到岛弧地形发生破碎, 进而引起强的内波混合。 相似文献
19.
Through extensive field data collection and analysis efforts conducted since the 1950s, researchers have established an understanding of the characteristic features of circulation in Puget Sound. The pattern ranges from the classic fjordal behavior in some basins, with shallow brackish outflow and compensating inflow immediately below, to the typical two-layer flow observed in many partially mixed estuaries with saline inflow at depth. An attempt at reproducing this behavior by fitting an analytical formulation to past data is presented, followed by the application of a three-dimensional circulation and transport numerical model. The analytical treatment helped identify key physical processes and parameters, but quickly reconfirmed that response is complex and would require site-specific parameterization to include effects of sills and interconnected basins. The numerical model of Puget Sound, developed using unstructured-grid finite volume method, allowed resolution of the sub-basin geometric features, including presence of major islands, and site-specific strong advective vertical mixing created by bathymetry and multiple sills. The model was calibrated using available recent short-term oceanographic time series data sets from different parts of the Puget Sound basin. The results are compared against 1) recent velocity and salinity data collected in Puget Sound from 2006 and 2) a composite data set from previously analyzed historical records, mostly from the 1970s. The results highlight the ability of the model to reproduce velocity and salinity profile characteristics, their variations among Puget Sound sub-basins, and tidally averaged circulation. Sensitivity of residual circulation to variations in freshwater inflow and resulting salinity gradient in fjordal sub-basins of Puget Sound is examined. 相似文献
20.
Resuspension rates have been measured on Long Island Sound sediments (New York/Connecticut, USA) under an oscillating grid,
using a flume, and in place, using high frequency acoustics, transmissometers, and sediment traps. Despite differences, the
results compare favorably. The methods all provide an order-of-magnitude estimate of the resuspension rate and increases under
storm conditions can be estimated. 相似文献
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