Spatial-temporal variability of submesoscale currents in the South China Sea

Spatial and seasonal variabilities of submesoscale currents in the northeastern South China Sea are investigated by employing a numerical simulation with a horizontal resolution of 1km. The results suggest that submesoscale currents are widespread in the surface mixed layer mainly due to the mixed layer instabilities and frontogenesis. In horizontal, submesoscale currents are generally more active in the north than those in the south, since that active eddies, especially cyclonic eddies, mainly occur in the northern area. Specifically, submesoscale currents are highly intensified in the east of Dongsha Island and south of Taiwan Island. In temporal sense, submesoscale currents are more active in winter than those in summer, since the mixed layer is thicker and more unstable in the winter. The parameterization developed by Fox-Kemper et al. is examined in terms of vertical velocity, and the results suggest that it could reproduce the vertical velocity if mixed layer instability dominates there. This study improves our understanding of the submesoscale dynamics in the South China Sea.

Morphology and distribution of the marine diatom Azpeitia africana(Janisch ex A. Schmidt) G. Fryxell & T. P. Watkins in the South China Sea

The purpose of the present paper is to study the morphological structure and variability of Azpeitia africana and to determine its geographical distribution in the surface sediments of the South China Sea(SCS). Sediment samples were collected with grabs or box corers in one cruise in 2001 and two cruises in 2007. The sampling stations were located between 3°56.61′–20°59.37′N and 108°30.68′–116°46.70′E,where the water depth ranged from 72 m to 4 238 m. The diatom was observed by phase contrast microscopy and scanning electron microscopy. Microscopical observation showed that A. africana had circular valves with the areolar lines radiating from the eccentric ring. The central rimoportula had an external tube recessed on the edge of a central ring. The marginal rimoportulae were not evenly spaced, and they were positioned more closely together in one quadrant than in the others. Azpeitia africana is the most abundant diatom species in the southern region of the SCS, and accounted for 0.9%–5.6% of all diatom species in the Xisha Islands area. Average cell density of A. africana was 1.1×10~5 valves/g. The percentage abundance of A.africana was low(0%–2.5%) in the northern regions of the SCS and the Sunda Shelf, and it was not detected in the northwestern continental shelf(shallow water area) and northern Kalimantan Island shelf. Our results suggested that A. africana is a typical warm water species and that it could be used as an indicator of the warm Paci?c Ocean water, including the Kuroshio Current, ?owing into the SCS.

Microfossils, carbonate lysocline and compensation depth in surface sediments of the northeastern South China Sea

Based on the quantitative analyses of abundance of planktonic foraminifera, benthic foraminifera, calcareous nannofossils, the ratios of calcareous to siliceous microfossils, and the determination of carbonate contents in the surface sediments of the northeastern South China Sea, it has been found that the carbonate contents, the abundance of planktonic foraminifera and calcareous nannoplankton, and the ratio of calcareous microfossils decrease rapidly while the ratio of the benthic foraminifera to the total foraminiferal fauna, specific value of siliceous microfossils, and the percentage of the agglutinated tests in the benthic foraminiferal fauna increase with the water depth. The results indicate that the microfossils abundance and ratio, and the carbonate content are closely related to the carbonate lysocline and carbonate compensation depth (CCD) in the study area. In addition, the carbonate lysocline and the CCD are different between the southern and northern parts of the South China Sea. Both the lysocline and the CCD are deeper in the south with 2 600 and 3 600 m than in the north with 2 200 and 3 400 m, respectively.

Combined effects of topography and bottom friction on shoaling internal solitary waves in the South China Sea

A numerical study to a generalized Korteweg-de Vries (KdV) equation is adopted to model the propagation and disintegration of large-amplitude internal solitary waves (ISWs) in the South China Sea (SCS). Based on theoretical analysis and in situ measurements, the drag coefficient of the Chezy friction is regarded as inversely proportional to the initial amplitude of an ISW, rather than a constant as assumed in the previous studies. Numerical simulations of ISWs propagating from a deep basin to a continental shelf are performed with the generalized KdV model. It is found that the depression waves are disintegrated into several solitons on the continental shelf due to the variable topography. It turns out that the amplitude of the leading ISW reaches a maximum at the shelf break, which is consistent with the field observation in the SCS.Moreover, a dimensionless parameter defining the relative importance of the variable topography and friction is presented.

Geochemical Characteristics of the Trace and Rare Earth Elements in Reef Carbonates from the Xisha Islands(South China Sea): Implications for Sediment Provenance and Paleoenvironment

Based on the concentrations of the trace elements,rare earth elements(REE),and Sr isotopic compositions in reef carbonates from the well‘Xike-1’reef core of the Xisha Islands,the constraints on sediment provenance and paleoenvironment were defined.Variations of the terrigenous input into the paleoseawater were traced in detail and the paleoenvironment and sediment provenance were further investigated.The results show that the HREE/LREE values in the reef carbonates are negatively associated with their Th and Al concentrations;however,their Al and Th concentrations show positive correlation.The lowest 87 Sr/86 Sr values in the reef carbonates generally coincide with the lowest values of Al,Th concentrations and the highest values of HREE/LREE.These data indicate that the HREE/LREE,Al concentrations,and Th concentrations of the reef carbonates are useful indexes for evaluating the influence of the terrigenous inputs on the seawater composition in the study area.From top to bottom,the changing process of the HREE/LREE values and Al,Th concentrations can be divided into 6 intervals;they are H1(0–89.30 m,about 0–0.11 Myr),L1(89.30–198.30 m,about 0.11–2.2 Myr),H2(198.30–374.95 m,about 2.2–5.3 Myr),D(374.95–758.40 m,about 5.3–13.6 Myr),L2(758.40–976.86 m,about 13.6–15.5 Myr),and H3(976.86–1200.00 m,about 15.5–21.5 Myr).Moreover,the changing trend of the HREE/LREE values coincides with that of the seawater δ^13C values recorded by benthonic foraminiferal skeletons from the drill core of ODP site 1148 in the South China Sea(SCS),but not with that of the seawaterδ18O values.The high uplifting rates of the Qinghai-Tibet Plateau coincide with the high Th and Al concentrations and the low HREE/LREE values in the reef carbonates.These data indicate that the main factors controlling the changes of terrigenous flux in the SCS are the tectonic activities associated with Qinghai-Tibet Plateau uplifting and the variations of uplifting rates rather than paleoclimatic changes.

RELATIONSHIP BETWEEN TROPICAL ISO AND TROPICAL CYCLONE ACTIVITY OVER THE SOUTH CHINA SEA

The relationship between the tropical intra-seasonal oscillation(ISO) and tropical cyclones(TCs) activities over the South China Sea(SCS) is investigated by utilizing the National Centers for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR) global reanalysis data and tropical cyclone best-track data from 1949 to 2009.The main conclusions are:(1)A new ISO index is designed to describe the tropical ISO activity over the SCS,which can simply express ISO for SCS.After examining the applicability of the index constructed by the Climate Prediction Center(CPC),we find that the convection spatial scale reflected by this index is too large to characterize the small-scale SCS and fails to divide the TCs activities over the SCS into active and inactive categories.Consequently,the CPC index can't replace the function of the new ISO index;(2)The eastward spread process of tropical ISO is divided into eight phases using the new ISO index,the phase variation of which corresponds well with the TCs activities over the SCS.TCs generation and landing are significantly reduced during inactive period(phase 4-6) relative to that during active period(phase 7-3);(3)The composite analyses indicate distinct TCs activities over the SCS,which is consistent with the concomitant propagation of the ISO convective activity.During ISO active period,the weather situations are favorable for TCs development over the SCS,e.g.,strong convection,cyclonic shear and weak subtropical high,and vice versa;(4)The condensation heating centers,strong convection and water vapor flux divergence are well collocated with each other during ISO active period.In addition,the vertical profile of condensation heat indicates strong ascending motion and middle-level heating over the SCS during active period,and vice versa.Thus,the eastward propagation of tropical ISO is capable to modulate TCs activities by affecting the heating configuration over the SCS.

Mechanism of Thermal Features over the Indo-China Peninsula and Possible Effects on the Onset of the South China Sea Monsoon

The thermal characteristics during the South China Sea (SCS) summer monsoon onset period near the Indo-China Peninsula are analyzed by using the South China Sea Monsoon Experiment (SCSMEX) reanalysis data from 1 May to 31 August 1998 and the NCEP/ NCAR pentad-mean reanalysis data from January 1980 to December 1995. The possible relationships between the anomaly of thermal features near the Indo-China Peninsula and the SCS monsoon onset are investigated, and the mechanism causing the SCS summer monsoon onset is also discussed. Results from the 1998 SCSMEX reanalysis data show that there exists a strong persistent surface sensible heating near the Indo-China Peninsula prior to the SCS monsoon onset, which has apparent low frequency oscillation features. This sensible healing leads lo a warmer center in the lower atmosphere near the Indo-China Peninsula and strong local horizontal temperature and geopotential height gradients which are favorable to strengthening the southwest wind over the Indo-China Peninsula. It is also found that stronger convergent winds at lower levels and stronger divergent winds at high levels appear, which provide a favorable configuration for the development of vertical motion, enhancement of precipitation, and onset of the SCS monsoon. These results can be verified by analysis of the multi-year mean data. Additionally, it is found that the temperature at 850 hPa increases more rapidly over the Indo-China Peninsula than the South China Sea prior to the SCS monsoon onset, which leads to a strengthening of the temperature difference between the Indo-China Peninsula and the South China Sea. Moreover, results from the analysis of the longitudinal temperature and geopotential height differences show that the eastern retreat of the subtropical high over the Indo-China Peninsula during the period of SCS monsoon onset is associated with the temperature increase over the Indo-China Peninsula and the eastern extension of low trough over the Bay of Bengal.

ANOMALIES OF ASIAN SUMMER MONSOON RELATED TO SSTA IN THE SOUTH CHINA SEA AND THE TROPICAL PACIFIC

SST data from 1945 to 1997 was used to analyze the interannual variability of SST in the South China Sea(SCS). Anomalous variations of the Asian summer monsoon related to the SCS SSTA were statistically investigated and compared with those related to the SSTA of the tropical Pacific. It was found that the anomalous pattern of the Asian summer monsoon related to the SCS SSTA is, to some extent, similar to that related to CEP(tropical central eastern Pacific), and contrary to that of WP(warm pool)SSTA.

东盟在“南海行为准则”磋商中立场的发展演变

作为世界上持续时间最长的外交互动之一,“南海行为准则”磋商进程自2013年启动以来时断时续,却在近几年取得了令人振奋的进展。纵观东盟在磋商中集体立场的演进,维护地区国家间和平关系、确保东盟中心性两大共同利益是促进东盟集体立场形成的主要动因;而成员国利益的差异性、东盟的组织特性则不时将东盟立场拖入困境。近年来中美关系的变化以及由此引发的美国政策因素则既凸显了东盟共同利益,又增加了其集体行动的难度。在共同利益驱动和集体行动困境的交替影响下,东盟立场虽然助力“准则”磋商取得了不错的成绩,但在进入细节化磋商后势必面临不确定性。为使磋商达到预期目标,通过“去小集团化”“去国际化”“去安全化”“去唯国际法化”和推进务实海洋合作的方式,构建以“东盟方式”为基底的“准则精神”,是未来东盟以集体立场促进磋商取得进展和“准则”发挥实际效力的关键所在。

竞合视域下的越南海洋国际合作

越南的海洋国际合作主要包括伙伴型竞合、争夺型竞合、适应型竞合三种类型。文章系统分析越南开展海洋合作的国际背景与国内政策主张,全面梳理越南与南海域外及周边国家开展海洋合作的概貌,搭建基于SWOT的竞合分析框架,研判各类型合作中的优势、劣势、机遇及威胁。分析显示,越南与域外大国的海洋合作增加了南海问题的复杂性;越南与中国等域内国家开展的海洋合作总体有益于南海的和平稳定。研究丰富了海洋合作理论和国际关系中的竞合理论,为加强中越在南海的合作、促进两国关系良性发展以及今后中国与其他南海周边国家开展海洋合作提供参考。

南海1998—2002年初级生产力的遥感估算及其时空演化机制

基于SeaWiFS资料得到1998—2002年海洋叶绿素浓度值以及海表温度(SST)数据和其它海洋数据,通过VGPM模型最终反演得到南海1998—2002年逐月初级生产力分布图以及季节分布图,发现在这5年内南海海域初级生产力年平均值变化不大,仅略有差异,1998年的年平均初级生产力要比其它几年的年平均初级生产力小一些;而南海海域初级生产力的季节变化则很明显,冬季要比其它几个季节高得多,而夏季最低。不同季节控制南海海域初级生产力的主导因素各不相同,主要是叶绿素浓度的分布、营养盐的分布、温度条件等,不同海区又略有不同。

1998年春夏南海温盐结构及其变化特征

利用 1 998年 5～ 8月“南海季风试验”期间“科学 1”号和“实验 3”号科学考察船两个航次CTD资料 ,分析了 1 998年南海夏季风暴发前后南海主要断面的温盐结构及其变化特征 .观测发现 ,南海腹地基本被典型的南海水团所控制 ,但在南海东北部尤其是吕宋海峡附近 ,表层和次表层水明显受到西太平洋水的影响 .季风暴发以后 ,南海北部表面温度有显著升高 ,升幅由西向东递减 ,而南海中部和南部表面温度基本没变 ,这使得南海北部东西向温度梯度和整个海盆南北向温度梯度均减小 .北部断面表层盐度普遍由 34以上降低到 34以下 ,混合层均有所发展 ,是季风暴发后降水和风力加剧的结果 .观测期间黑潮水跨越吕宋海峡的迹象明显但变化剧烈 .4～ 5月 ,黑潮次表层水除在吕宋海峡中北部出现外 ,在吕宋岛以西亦有发现 ,表明有部分黑潮水从吕宋海峡南端沿岸向西进而向南进入南海 .6～ 7月 ,次表层高盐核在吕宋海峡中北部有极大发展 ,但在吕宋岛以西却明显萎缩 ;虽然看上去黑潮水以更强的流速进、出南海 ,但对南海腹地动力热力结构的影响未必更大 .一个超过 34.55的表层高盐水体于巴拉望附近被发现 ,似与通过巴拉望两侧水道入侵南海的西太平洋水有关 .

2013年5月华南强降水与中国南海夏季风爆发

利用2013年"华南季风强降水外场试验与研究"的外场试验数据、美国NCEP FNL资料和卫星云顶黑体辐射温度资料,对2013年5月7—17日华南地区出现的两次强降水过程(7—12日和14—17日)中的高低空环流以及相关气象要素场的变化进行了对比分析。中国南海夏季风于5月第3候建立,两次过程分处于夏季风爆发前后。通过对比影响两次强降水过程的主要环流系统如南亚高压、高空副热带西风急流、500 hPa环流型、水汽来源等,指出影响两次强降水过程大尺度环流场之间的显著区别,说明南海季风爆发前后大尺度环流场对暴雨影响的典型差异。7—12日过程主要受北方锋面影响和南方暖湿气流辐合作用,导致华南地区出现南北两条雨带。14—17日过程则由于季风爆发后强的暖湿空气活动致使华南地区对流活跃,从而形成一条位于广东北部的雨带,此次过程强降水比第1次过程集中且对流性更强。两次降水过程的内在物理机制是一个准平衡态的热力适应过程,由于第2次过程降水更强,导致热源作用明显增强,动力向热力的适应过程也更显著。利用探空资料揭示出两次过程暖区暴雨大气热力和动力条件存在显著区别,7—12日南海季风爆发前的暖区暴雨主要受低层强垂直风切变导致的大气斜压不稳定影响;14—17日南海季风爆发后的暖区暴雨主要受高低空急流的强耦合作用影响。

南海海域BT资料、南森站资料计算温跃层——三项示性特征的比较

南海海域海水温度调查资料主要为 BT 资料和南森站资料两种类型，为比较两种资料计算的温度跃层三项示性特征的区别，本文用同一种温跃层识别、统计方法分别对两种类型资料进行了判别和统计，在此基础上，绘制了南海冬、夏季跃层强度分布图。结果表明，两种类型的调查资料在计算浅温度跃层强度和上界深度上有较明显区别，BT 资料的温跃层强度计算结果大于南森站资料，温度跃层上界较南森站资料深，温跃层厚度亦有差别，但规律不明显。两种类型资料对深温度跃层三项示性特征值的计算结果差异不明显。

南海及周围地区的现今构造运动

利用南海及其周围地区的GPS数据,分析南海及周围地区速度场和应变场的空间变化,以及相邻块体之间的相对运动。研究发现,南海现今仍在继续扩张,西部是从其北边缘向南沿NW-SE方向逐渐扩张的,东部是从中心向北与向南逐渐扩张的。由主张应变率计算的中央海盆近SN方向的平均扩张速率为3.1 mm/a。在南海东部(117.0°E),南北之间(11°～22°N)SN方向的扩张速率为9.3 mm/a,小于65M a以来NNW-SSE方向13.0 mm/a的平均扩张速率。南海的扩张运动是印度板块、太平洋和菲律宾海板块与欧亚板块之间的相互作用,以及南海地区地幔物质上涌共同作用的结果。

天然气水合物资源量的一种估算方法——以南海北部陆坡为例

根据天然气水合物物理化学相图平衡的基本原理,运用微积分学的基本理论,尝试一种新的天然气水合物资源量计算方法,并以南海北部陆坡为例对天然气水合物资源量进行了初步估算。天然气水合物稳定分布区可看成由许多微体积单元组成,对所有微体积单元进行累积积分计算出天然气水合物的分布体积;然后结合世界上已知天然气水合物分布的有关参数(如天然气水合物沉积层的孔隙度、天然气水合物的饱和度和水合系数)估算南海北部陆坡天然气水合物的潜在资源量。估算结果为,南海北部陆坡天然气水合物资源量约相当于标准条件下6.3×1013m3的天然气,这与美国Blake海底高原、日本Nankai海槽、美国墨西哥湾北部天然气水合物资源甲烷量的数量级(1013m3)一致,显示了南海北部陆坡天然气水合物资源的巨大前景。当然,南海北部陆坡天然气水合物的潜在资源量还有待于进一步调查核实。

1997年东亚夏季风异常活动在汛期降水中的作用

利用 1 997年逐日降水资料和国家气象中心提供的T6 3再分析资料 ,详细讨论了中国汛期降水及东亚夏季风活动的异常特征及其间的联系。结果表明 ,该年中国夏季降水及东亚夏季风活动均表现了突出的异常 ,东部雨带长期滞留在江南、华南一带 ,夏季风向北的推进很弱 ,主要活跃于较低纬度 ,最北仅至 3 5°N ,未能在黄河以北的地区建立 ,比起气候意义下夏季风北进的最高纬度偏南 1 0°左右。在这一过程中 ,夏季风异常是主要雨带异常发展的重要影响因子 ,候大雨带的建立和北推均与季风的建立与活跃密切相关。进一步对大尺度水汽场的分析表明 ,夏季风的活动明显改变了大尺度水汽输送及辐合 ,进而影响和制约了主要雨带的分布。夏季风爆发后 ,南海及中国大陆的主要水汽输送源均发生了明显变化 ,来自于孟加拉湾和热带印度洋的水汽输送到南海后 ,再从南海输送到中国大陆。而季风的活动同时也制约了强水汽辐合带的出现 。

南海海面温度的年际模态及其与季风强迫的关系

通过对COADS和OISST海洋气象资料的分析,以南海的海面温度异常(SSTA)为指示因子,在研究年际尺度上的南海与大尺度ENSO关系的基础上,进一步探讨了季风强迫下Ekman抽吸对 SSTA年际变化的贡献。研究发现,南海 SSTA滞后5个月时与 Nino 3的 SSTA相关系数最大,且其年际变化依方差贡献大小,分别有42.7月、25.6月及36.6个月的周期,这3个年际模态基本上能够描述海面温度的年际变异,为南海在大尺度ENSO背景下存在区域响应提供了重要的证据;应用Krause Turner混合层温度方程对南海异常暖事件的研究表明,除了经向风应力异常,Ekman抽吸也是影响SSTA年际变异的主要因素,在某些异常年份甚至是主导因素,为南海SSTA年际变化的研究提供了重要的补充。

南海沉积物中天然气水合物饱和度与声学特性的关系

中国南海蕴藏丰富的天然气水合物（气水合物）资源，研究其赋存区沉积物中气水合物的声学响应特征，对南海气水合物的调查和资源估算具有重要意义。利用新型弯曲元探测技术和套管型时域反射技术（TDR），采用模拟实验手段研究了南海神狐海域沉积物中气水合物形成的声学响应特征，发现在气水合物饱和度（Sn）为0～14％时，声波信号随气水合物形成而逐渐减弱，而当Sn〉14％后．声波信号渐渐增强；气水合物形成过程中，纵、横波速度（vp、vs）随Sb的增加而增大，且轧在Sn〉14％后增长速度加快。这些现象表明，气水合物在南海沉积物中可能先在孔隙流体中以微粒子的状态生成，对声波造成了较大的散射衰减，导致声波信号变弱，但对剪切模量的贡献不明显；当Sb高于14％后，微粒子数量的增多使气水合物聚集，并与沉积物颗粒接触，从而加快了73，的增长。

苏门答腊地区对流活动及其与南海夏季风建立的关系

使用日本气象厅提供的1980—1997年TBB资料和NCEP/NCAR40a逐日再分析资料,分析了苏门答腊地区对流活动特征及其与南海夏季风建立的关系,发现南海夏季风的建立与冬季位于苏门答腊的对流中心由冬入夏沿"大陆桥"和中南半岛的系统性移动有密切联系。苏门答腊地区对流沿"大陆桥"移动加快是一个先兆信号,正是对流移动的突然加速,对随后中南半岛对流增强有直接影响;中南半岛地区对流爆发引起副热带高压带在该地区断裂从而导致了南海地区对流活跃和夏季风的建立。南海夏季风爆发之前,南海地区与苏门答腊地区的对流呈偶极型分布;南海地区和苏门答腊南部地区的对流变化几乎呈反相关关系,南海夏季风爆发之前,苏门答腊南部地区对流旺盛;南海地区对流增强期间,苏门答腊南部地区对流减弱。由此可以把南海地区与苏门答腊南部TBB之差小于等于5K(并维持1候)的开始日期作为南海夏季风爆发的指标之一。