中国南海区1992-2012年的中尺度涡旋演化过程表达与统计分析     

杜云艳  易嘉伟  吴笛  贺志刚  王东晓  梁福源 《海洋学报(英文版)》2014,33(11):36-47

Automated identification and tracking of mesoscale ocean eddies has recently become one research hotspot in physical oceanography. Several methods have been developed and applied to survey the general kinetic and geometric characteristics of the ocean eddies in the South China Sea（SCS）. However, very few studies attempt to examine eddies＇ internal evolution processes. In this study, we reported a hybrid method to trace eddies＇ propagation in the SCS based on their internal structures, which are characterized by eddy centers, footprint borders, and composite borders. Eddy identification and tracking results were represented by a GIS-based spatiotemporal model. Information on instant states, dynamic evolution processes, and events of disappearance, reappearance, split, and mergence is stored in a GIS database. Results were validated by comparing against the ten Dongsha Cyclonic Eddies（DCEs） and the three long-lived anticyclonic eddies（ACEs） in the northern SCS, which were reported in previous literature. Our study confirmed the development of these eddies. Furthermore, we found more DCE-like and ACE-like eddies in these areas from 2005 to 2012 in our database. Spatial distribution analysis of disappearing, reappearing, splitting, and merging activities shows that eddies in the SCS tend to cluster to the northwest of Luzon Island, southwest of Luzon Strait, and around the marginal sea of Vietnam. Kuroshio intrusions and the complex sea floor topography in these areas are the possible factors that lead to these spatial clusters.  相似文献   

Origin and anatomy of two different types of mass–transport complexes: A 3D seismic case study from the northern South China Sea margin     

《Marine and Petroleum Geology》2014

Integration of 2D and 3D seismic data from the Qiongdongnan Basin along the northwestern South China Sea margin has enabled the seismic stratigraphy, seismic geomorphology and emplacement mechanisms of eight separate, previously undocumented, mass–transport complexes (MTCs) to be characterized. These eight MTCs can be grouped into two types:(1) Localized detached MTCs, which are confined to submarine canyons and cover hundreds of km², consist of a few tens of km³ remobilized sediments and show long striations at their base. They resulted from small-scale mass-wasting processes induced by regional tectonic events and gravitational instabilities on canyon margins.(2) Regional attached MTCs, which occur within semi-confined or unconfined settings and are distributed roughly perpendicular to the strike of the regional slope. Attached MTCs occupy hundreds to thousands of km² and are composed of tens to hundreds of km³ of remobilized sediments. They contain headwall escarpments, translated blocks, remnant blocks, pressure ridges, and basal striations and cat-claw grooves. They were created by large-scale mass-wasting processes triggered by high sedimentation rates, slope oversteepening by shelf-edge deltas, and seismicity.Our results show that MTCs may act as both lateral and top seals for underlying hydrocarbon reservoirs and could create MTC-related stratigraphic traps that represent potential drilling targets on continental margins, helping to identify MTC-related hydrocarbon traps.  相似文献   

琼东南盆地深水区构造热演化特征及其影响因素分析   总被引：5，自引：1，他引：4  

王振峰  施小斌  杨军  黄保家  孙珍  WANG Yahui  蒋海燕  于传海  杨小秋 《海洋学报(英文版)》2014,33(12):107-117

To reveal the tectonic thermal evolution and influence factors on the present heat flow distribution, based on 154 heat flow data, the present heat flow distribution features of the main tectonic units are first analyzed in detail, then the tectonic thermal evolution histories of 20 profiles are reestablished crossing the main deep-water sags with a structural, thermal and sedimentary coupled numerical model. On the basis of the present geothermal features, the Qiongdongnan Basin could be divided into three regions: the northern shelf and upper slope region with a heat flow of 50–70 m W/m2, most of the central depression zone of 70–85 m W/m2, and a NE trending high heat flow zone of 85–105 m W/m2 lying in the eastern basin. Numerical modeling shows that during the syn-rift phase, the heat flow increases generally with time, and is higher in basement high area than in its adjacent sags. At the end of the syn-rift phase, the heat flow in the deepwater sags was in a range of 60–85 m W/m2, while in the basement high area, it was in a range of 75–100 m W/m2. During the post-rift phase, the heat flow decreased gradually, and tended to be more uniform in the basement highs and sags. However, an extensive magmatism, which equivalently happened at around 5 Ma, has greatly increased the heat flow values, and the relict heat still contributes about 10–25 m W/m2 to the present surface heat flow in the central depression zone and the southern uplift zone. Further analyses suggested that the present high heat flow in the deep-water Qiongdongnan Basin is a combined result of the thermal anomaly in the upper mantle, highly thinning of the lithosphere, and the recent extensive magmatism. Other secondary factors might have affected the heat flow distribution features in some local regions. These factors include basement and seafloor topography, sediment heat generation, thermal blanketing, local magmatic injecting and hydrothermal activities related to faulting and overpressure.  相似文献   

Full retention in tuna fisheries: Benefits,costs and unintended consequences     

《Marine Policy》2014

Several tuna regional fisheries management organizations (t-RFMOs) have adopted retention requirements for skipjack, bigeye and yellowfin tunas caught by purse seine vessels to reduce discards, create disincentives to catch small fish, and incentivize the development and adoption of more selective technologies. Although retention policies in the t-RFMOs have been limited to target tunas in purse seine fisheries, some have advocated for an expansion of those policies, and t-RFMOs could consider expanding retention policies to a greater number of species and/or to other gear types. This paper discusses the benefits and costs of broader retention policies for purse seine and longline tuna fisheries in the western and central Pacific Ocean (WCPO). Using bycatch data from observers and logbooks from the U.S. purse seine and longline fleets operating in the WCPO, this paper documents the types and magnitude of fish discarded. For the purse seine fishery, this information was used to estimate direct impacts of having to off-load at the initial point of landing in key Pacific Island ports. For the longline fishery, estimates of direct impacts were limited to Honolulu and Pago Pago, American Samoa, the two primary ports where U.S. catch is landed. Expanding retention policies beyond the target tunas and to other gear types would further reduce discarding and possibly provide stronger incentives to develop and use more selective techniques. Beyond impacts to the ecosystem and fisher behavior, adopting broader retention policies may have other implications, and this paper explores those implications on vessels, processors, and communities. In general, as is the case with most direct interventions on fishing operations, there will be both benefits and costs, and the magnitude of those impacts will depend on the scope and extent of any expanded retention policy.  相似文献   

Delving into three-dimensional structure of the West Luzon Eddy in a regional ocean model     

《Deep Sea Research Part I: Oceanographic Research Papers》2014

The three-dimensional structure and associated dynamics of the prominent cold (cyclonic) West Luzon Eddy (WLE) were investigated by a high-resolution regional ocean model. The WLE was horizontally and vertically heterogeneous, exhibiting asymmetric structures in the circulation, vorticity, vertical motion and energy distributions within the eddy. The asymmetry was mainly attributed to the existence of an eddy dipole formed by a coexisting warm (anti-cyclonic) eddy to the south of the WLE. Analysis of the momentum balance revealed that the coexistence of two eddies intensified barotropic pressure gradients in the southern WLE to locally enhance the eastward jet. The positive (negative) vorticity of the jet strengthened (weakened) the eddy in the southern sector (periphery), which, together with the formation of a subsurface density front, intensified (suppressed) the corresponding upward motion and cooling. The baroclinic pressure gradients opposed the dominant barotropic components and spun down the eddy at greater depths with stronger weakening in the southern sector near the front. Asymmetric energy distributions showed that larger mean kinetic energy (MKE) and eddy available potential energy (EAPE) were stored in the southern sector of the WLE. While the larger MKE was directly linked with the stronger barotropic currents, the larger EAPE in the southern WLE was formed by baroclinic energy conversions due to a strong density gradient at the front.  相似文献   

Physical and biological controls on the summer chlorophyll bloom to the east of Vietnam   总被引：1，自引：0，他引：1  

Gengxin Chen  Peng Xiu  Fei Chai 《Journal of Oceanography》2014,70(3):323-328

The contributions of physical and biological processes to the chlorophyll-a (Chl-a) bloom to the east of Vietnam in summer are examined. The offshore jet redistributes Chl-a concentration by transporting high Chl-waters from the continental margin to the east of Vietnam. The jet also contributes to high concentrations of nutrients and zooplankton biomass that lead to a dynamic balance between increased nutrients and grazing pressure for phytoplankton growth. As a consequence, the net biological processes reduce the Chl-a concentrations in the broader offshore region, but they also maintain the filaments with higher Chl-a stretching away from the coast due to the reduced grazing pressure.  相似文献   

Ocean Model Open Boundary Conditions with Volume,Heat and Salinity Conservation Constraints简     

WANG Qiang  ZHOU Weidong  WANG Dongxiao  DONG Danpeng 《大气科学进展》2014,31(1):188-196

Open boundary conditions （OBCs） for a regional ocean model that can be integrated stably over a long timeframe, as well as satisfy the volume, heat and salinity conservation constraints, were developed. First, the idea that the inward and outward flux information can be treated separately in the OBCs was adopted. Second, in order to maintain the property that the volume, heat and salinity remains conserved in the simulation domain, conservation constraints were added to the OBCs, and an inverse method utilized to solve the constraint equations. Ideal experiments were designed to investigate the conservation property, and the OBCs were found to work efficiently to maintain the volume, heat and salinity conservation. It was found that simulations were comparable to observations when the OBCs were applied to a regional ocean model.  相似文献   

The mechanism of post-rift fault activities in Baiyun sag,Pearl River Mouth basin     

《Journal of Asian Earth Sciences》2014

Post-rift fault activities were often observed in deepwater basins, which have great contributions to oil and gas migration and accumulation. The main causes for post-rift fault activities include tectonic events, mud or salt diapirs, and gravitational collapse. In the South China Sea continental margin, post-rift fault activities are widely distributed, especially in Baiyun sag, one of the largest deepwater sag with its main body located beneath present continental slope. During the post-rift stage, large population of faults kept active for a long time from 32 Ma (T70) till 5.5 Ma (T10). Seismic interpretation, fault analysis and analogue modeling experiments indicate that the post-rift fault activities in Baiyun sag between 32 Ma (T70) and 13.8 Ma (T30) was mainly controlled by gravity pointing to the Main Baiyun sag, which caused the faults extensive on the side facing Main Baiyun sag and the back side compressive. Around 32 Ma (T70), the breakup of the continental margin and the spreading of the South China Sea shed a combined effect of weak compression toward Baiyun sag. The gravity during post-rift stage might be caused by discrepant subsidence and sedimentation between strongly thinned sag center and wing areas. This is supported by positive relationship between sedimentation rate and fault growth index. After 13.8 Ma (T30), fault activity shows negative relationship with sedimentation rate. Compressive uplift and erosion in seismic profiles as well as negative tectonic subsiding rates suggest that the fault activity from 13.8 Ma (T30) to 5.5 Ma (T10) might be controlled by the subductive compression from the Philippine plate in the east.  相似文献   

南海西部海底巨型麻坑活动性示踪研究     

关永贤  罗敏  陈琳莹  王淑红  颜文  王宏斌  陈多福 《地球化学》2014,(6):628-639

南海西部陆坡海域海底广泛发育麻坑,其规模和数量在世界范围内均属罕见,但关于它们目前的活动特征尚不清楚。通过对西沙隆起西南部麻坑区采集的两根沉积柱样孔隙水SO^2–4、K^＋、Mg^2＋、Ca^2＋、Sr^2＋以及溶解有机碳（DIC）含量随深度的变化特征的研究,揭示麻坑内与硫酸根消耗有关的生物地球化学过程,并推断麻坑目前的活动状况。采集于麻坑外的C9柱样SO^2–4浓度变化整体呈向下凹的形态降低,减少的硫酸根是被有机质硫酸盐还原作用消耗。采集于麻坑内的C14柱样SO^2–4浓度梯度呈现明显的三段式变化,0.00-0.66 m内SO2–4浓度变化主要受有机质硫酸盐还原作用控制,0.66-3.70 m受有机质硫酸盐还原和甲烷缺氧氧化共同控制,3.70 m以下部分主要受甲烷缺氧氧化作用的影响。根据C14柱样3.7 m以下孔隙水硫酸根浓度梯度计算的硫酸根-甲烷交接带（SMI）约在14.3 m处,甲烷向上扩散的通量约为0.0144 mol/（m^2·a）。此外,2个柱样沉积物孔隙水的Ca^2＋浓度均随深度明显降低,而Mg2＋浓度略微降低,主要与自生碳酸盐矿物沉淀有关。C14的Mg/Ca和Sr/Ca随深度变化指示该柱样沉积物中自生碳酸盐岩矿物主要为高镁方解石。2个柱样的孔隙水地球化学特征显示目前研究区麻坑活动不活跃, C14麻坑中含甲烷流体发生微弱渗漏,可能处于麻坑活动的衰落期。  相似文献   

On improving tropical cyclone track forecasts using a scale-selective data assimilation approach: a case study     

Zhijuan Lai  Sai Hao  Shiqiu Peng  Bei Liu  Xiangqian Gu  Yu-Kun Qian 《Natural Hazards》2014,73(3):1353-1368

A dynamical downscaling approach based on scale-selective data assimilation (SSDA) is applied to tropical cyclone (TC) track forecasts. The results from a case study of super Typhoon Megi (2010) show that the SSDA approach is very effective in improving the TC track forecasts by fitting the large-scale wind field from the regional model to that from the global forecast system (GFS) forecasts while allowing the small-scale circulation to develop freely in the regional model. A comparison to the conventional spectral-nudging four-dimensional data assimilation (FDDA) indicates that the SSDA approach outperforms the FDDA in TC track forecasts because the former allows the small-scale features in a regional model to develop more freely than the latter due to different techniques used. In addition, a number of numerical experiments are performed to investigate the sensitivity of SSDA’s effect in TC track forecasts to some parameters in SSDA, including the cutoff wave number, the vertical layers of the atmosphere being adjusted, and the interval of SSDA implementation. The results show that the improvements are sensitive in different extent to the above three parameters.  相似文献