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151.
Ching-Hui Tsai Shu-Kun Hsu Yi-Ching Yeh Chao-Shing Lee Kanyuan Xia 《Marine Geophysical Researches》2004,25(1-2):63-78
Magnetic data suggest that the distribution of the oceanic crust in the northern South China Sea (SCS) may extend to about 21 °N and 118.5 °E. To examine the crustal features of the corresponding continent–ocean transition zone, we have studied the crustal structures of the northern continental margin of the SCS. We have also performed gravity modeling by using a simple four-layer crustal model to understand the geometry of the Moho surface and the crustal thicknesses beneath this transition zone. In general, we can distinguish the crustal structures of the study area into the continental crust, the thinned continental crust, and the oceanic crust. However, some volcanic intrusions or extrusions exist. Our results indicate the existence of oceanic crust in the northernmost SCS as observed by magnetic data. Accordingly, we have moved the continent–ocean boundary (COB) in the northeastern SCS from about 19 °N and 119.5 °E to 21 °N and 118.5 °E. Morphologically, the new COB is located along the base of the continental slope. The southeastward thinning of the continental crust in the study area is prominent. The average value of crustal thinning factor of the thinned continental crust zone is about 1.3–1.5. In the study region, the Moho depths generally vary from ca. 28 km to ca. 12 km and the crustal thicknesses vary from ca. 24 km to ca. 6 km; a regional maximum exists around the Dongsha Island. Our gravity modeling has shown that the oceanic crust in the northern SCS is slightly thicker than normal oceanic crust. This situation could be ascribed to the post-spreading volcanism or underplating in this region. 相似文献
152.
153.
Roles of Continental Shelves and Marginal Seas in the Biogeochemical Cycles of the North Pacific Ocean 总被引:4,自引:0,他引:4
Chen-Tung Arthur Chen Andrey Andreev Kyung-Ryul Kim Michiyo Yamamoto 《Journal of Oceanography》2004,60(1):17-44
Most marginal seas in the North Pacific are fed by nutrients supported mainly by upwelling and many are undersaturated with
respect to atmospheric CO2 in the surface water mainly as a result of the biological pump and winter cooling. These seas absorb CO2 at an average rate of 1.1 ± 0.3 mol C m−2yr−1 but release N2/N2O at an average rate of 0.07 ± 0.03 mol N m−2yr−1. Most of primary production, however, is regenerated on the shelves, and only less than 15% is transported to the open oceans
as dissolved and particulate organic carbon (POC) with a small amount of POC deposited in the sediments. It is estimated that
seawater in the marginal seas in the North Pacific alone may have taken up 1.6 ± 0.3 Gt (1015 g) of excess carbon, including 0.21 ± 0.05 Gt for the Bering Sea, 0.18 ± 0.08 Gt for the Okhotsk Sea; 0.31 ± 0.05 Gt for
the Japan/East Sea; 0.07 ± 0.02 Gt for the East China and Yellow Seas; 0.80 ± 0.15 Gt for the South China Sea; and 0.015 ±
0.005 Gt for the Gulf of California. More importantly, high latitude marginal seas such as the Bering and Okhotsk Seas may
act as conveyer belts in exporting 0.1 ± 0.08 Gt C anthropogenic, excess CO2 into the North Pacific Intermediate Water per year. The upward migration of calcite and aragonite saturation horizons due
to the penetration of excess CO2 may also make the shelf deposits on the Bering and Okhotsk Seas more susceptible to dissolution, which would then neutralize
excess CO2 in the near future. Further, because most nutrients come from upwelling, increased water consumption on land and damming
of major rivers may reduce freshwater output and the buoyancy effect on the shelves. As a result, upwelling, nutrient input
and biological productivity may all be reduced in the future. As a final note, the Japan/East Sea has started to show responses
to global warming. Warmer surface layer has reduced upwelling of nutrient-rich subsurface water, resulting in a decline of
spring phytoplankton biomass. Less bottom water formation because of less winter cooling may lead to the disappearance of
the bottom water as early as 2040. Or else, an anoxic condition may form as early as 2200 AD.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
154.
On the basis of the data of oceanographic survey in the East China Sea in four seasons during 1997-2000 (23°30'~33°00'N, 118°30'-128°E), the variation of total biomass and diet biomass of zooplankton and their spatial-temporal distribution and relationship with the fishing ground of Engraulis japonicus are approached and analyzed. The results show that the average biomass is 65.32 mg/m3 in four seasons, autumn (86.18 mg/m3) being greater than summer (69.18 mg/m3) greater than spring (55.67 mg/m3) greater than winter (50.33 mg/m3). The average value of diet zooplankton biomass is 40.9 mg/m3. The trends of horizontal distribution both in the total biomass and the diet biomass of zooplankton are similar. The high biomass region (250-500 mg/m3) is very limited, only accounting for 1% of the investigation area. Seasonal variation of the biomass is very remarkable in the west and north parts of East China Sea coastal waters ( 29°30'N,125°E). The horizontal distribution of diet zooplankton depends on the 相似文献
155.
应用勘探层分析及石油资源专家系统对XH凹陷下第三系勘探目的层的三个勘探层烃资源量作出了综合预测,结果表明,凹陷内各勘探层,尤其是渐新统勘探层,烃资源量相当可观。提出在渐新统内的地层圈闭中可进一步作详细的勘探工作。 相似文献
156.
南海南部大陆架的残留沉积 总被引:1,自引:0,他引:1
研究了南海南部大陆架的残留沉积物的粒度、石英砂表面结构特征、生物分布等,并指出残留沉积普遍遭受改造。按其早期的形成环境差异和改造作用不同,划分出加里曼丹-巴拉望残留沉积区和亚南巴斯-纳土纳残留沉积区。 相似文献
157.
在南海北部利用地球化学方法作为油气勘探的一种辅助手段。在6个航次中采集了沉积物、底层海水及海面大气样品,测定了近50种化探指标,并采用稳健统计方法进行了数据处理和异常圈定。化探结果在油气藏上方发现了清晰的、具不同指标组合的综合化探异常,与邻近空构造形成鲜明的对照。圈闭顶部的块状异常和圈闭周绿的环状、半环状异常是下伏油气藏的良好指示,而剖面上呈锯齿状、平面上呈线状的异常则与断裂带有关。实践表明,建立已知油气藏上方的化探异常模式及解剖已知空构造上方的地球化学特征对于指导本区或邻区的化探异常评价是十分必要的。 相似文献
158.
热带气旋活动对中国夏季雨带类型与ENSO的响应关系 总被引:2,自引:0,他引:2
本文分析研究了热带气旋1)活动与中国夏季2)3组(包括8种)主要多雨带类型的响应关系。同时对热带气旋活动与夏季大陆气温和ENSO事件的始终时间的响应关系,也进行了探讨。分析表明,夏季中国的雨带分布特征对热带气旋活动有着十分重要的指示意义。热带气旋活动与中国大陆气温有着正相关关系,与ENSO事件的发生有着反相关关系 相似文献
159.
以上海市向阳圩海塘围堰主堤为工程背景,在大量原位实测的基础上通过对各测试结果的统计分析研究了软土海滩围堰堤坝及地基沉降位移特性。结果表明:围堰堤坝及地基沉降具有显著的时效特性,沉降与时间的相关关系可用负指数时效特性曲线拟合;各测点位移值随时间具有明显突变变化,整个沉降时域可分为快速沉降时域区及缓慢沉降时域区。同时,在充分考察了沉降速率随时间变化特性的前提下提出了用该参量预测堤坝稳定时间及最终沉降位移的建议。 相似文献
160.
A tether management system of a winch module in a marine environment is proposed. For the purpose of this study the subsea body is considered as a mass attached at the free end of a long tether which is wrapped around a circular drum controlled by an external torque. The winch is considered mounted on a heaving platform. The effect of the heaving platform on the motions of the drum, tether and attached mass are studied with respect to the longitudinal vibrations of the tether in one dimension. The hydrodynamic effects are considered on the deployed portion of the tether and the tethered mass, both of which are assumed submerged in otherwise still water. The resulting nonlinear system of equations of motion is developed and solved numerically for an example of a marine tether system. The effect of the tether extensibility on the operation threshold of the system is identified. Comparison with an inextensible tether case is provided. The numerical results and their analysis for the retrieval/deployment of the system are presented. 相似文献