Institutional Repository of South China Sea Institute of Oceanology, CAS
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Heat budget of the western Pacific warm pool and the contribution of eddy heat transport diagnosed from HYCOM assimilation
No full textUsing the high-resolution Hybrid Coordinate Ocean Model and the Navy Coupled Ocean Data Assimilation Global 1/12A degrees Analysis (GLBa0.08), and the Objectively Analyzed Air-Sea Fluxes and the International Satellite Climatology Cloud Project products, we investigated the seasonal and interannual evolutions of heat budget, including the pseudo-heat content change, the net air-sea heat flux and the eddy heat transport (EHT), based on the time-dependent heat budget analysis in the western Pacific warm pool (WPWP). The results show that the pseudo-heat content change has significant semi-annual variation, which peaks in April-May and September. There is strong positive feedback between EHT and the net air-sea heat flux. EHT is important in balancing the sea surface heat flux into the WPWP. The seasonal EHT variability is dominated by its meridional component. On the interannual time scale, the zonal and vertical components of EHT show comparable amplitudes with the meridional one. The observed net air-sea heat flux in the WPWP is highly correlated with EHT and the pseudo-heat content change on the interannual time scale. The net air-sea heat flux leads the pseudo-heat content change by about half a month and leads EHT by about one month. The variations of the air-sea heat flux and EHT are connected to the El Nio Southern Oscillation events: during the development of El Nio (La Nia) events, the warm pool expanded eastward (retreated westward), the net air-sea surface flux into the WPWP increased (decreased) and EHT enhanced (weakened) significantly
New insights into the magmatism in the northern margin of the South China Sea: Spatial features and volume of intraplate seamounts
No full textThe extensive intraplate seamounts are obvious features in the northern South China Sea (SCS). However, the distribution, volume, and origin of these seamounts are not well understood, which greatly hinders our understanding of magmatism in the SCS. Based on high-resolution bathymetric data and 147 seismic profiles, and combining gravity and magnetic data, we first identify 45 seamounts in the northern margin of the SCS and simulate their shape with elliptical cones. Results show that the total volume of these 45 seamounts above seafloor is estimated at about 1885-3078 km(3) and the total volume of intrusive magma above Moho is about 0.15 Mkm(3), which is close to the estimates for classic large igneous provinces across the world. These seamounts are mostly located on the continental slope with thin crust (approximately 12-18 km), which reduces the overlying pressure and shortens the magmatic conduits. The dominant azimuth of elliptical major axis in seamounts is consistent with the synrift and synspreading fault strikes (NE-NEE), indicating that these preexisting faults provide magmatic conduits for the subsequent postrift intraplate seamounts. Based on three existing clues, i.e., (1) the intraplate seamounts, high velocity layer and Hainan mantle plume are contiguous in 3-D space, (2) the high-velocity layer is thicker beneath the continental shelf but thinner beneath the slope, and (3) the basalts dredged from certain seamounts show OIB-type geochemical features, we propose a magmatic upwelling pattern which contains Hainan mantle plume to explain the spatial and morphological characteristics of these intraplate seamounts
Phytoplankton bloom triggered by an anticyclonic eddy: The combined effect of eddy-Ekman pumping and winter mixing
No full textRecent composite based researches reveal that anticyclonic eddies facilitate the growth of phytoplankton in the subtropical gyres. Two dynamical mechanisms, eddy-Ekman pumping and winter mixing, have been examined individually, but their relative and combined effects remain unclear. Using satellite observations and model simulations, this study investigated the process of a distinct phytoplankton bloom generated in an anticyclonic eddy in the nutrient-depleted southeastern Indian Ocean. The bloom propagated westward along with the eddy for more than 600 km from late April to August in 2010. The peak of surface chlorophyll concentration in the eddy is 2.2 times larger than the mean value of the ambient. The development of the bloom is dominated by the winter deepening of mixed layer, whose velocity in vertical nutrient flux is on average 3 times larger than that of eddy-Ekman pumping. The results of a 1-D physical-biogeochemical model demonstrate that the role of eddy-Ekman pumping is also indispensable, because it not only transports extra nutrients into the mixed layer, but also results in significant chlorophyll enrichment in subsurface water. The superposition of eddy-Ekman pumping on winter mixing triples the chlorophyll both at the surface and in the upper layer, and the entrainment of subsurface phytoplankton into the mixed layer contributes significantly to the surface bloom, especially in its initial stage. Both the satellite observations and model simulation show that eddy-Ekman pumping can lead to an early occurrence of the bloom for more than 2 weeks
Radiolarian biogeography in surface sediments of the Northwest Pacific marginal seas
No full textOverall abundance and species composition of radiolarian faunas were analyzed in surface sediment samples from representative areas of South China Sea, East China Sea, Sea of Japan, Sea of Okhotsk, Bering Sea, Philippine Sea, and the western boundary current regions of the North Pacific, in order to understand the biogeographic distribution of radiolarians in the Northwest Pacific and explore its relationship with the main environmental factors and the North Pacific circulation. The results showed that radiolarians in the Northwest Pacific surface sediments can be divided into two large biogeographic provinces-cluster A and cluster B. Cluster A is characterized by the dominance of warm-water species and distributed primarily in tropical and subtropical seas with high radiolarian abundance and diversity; whereas cluster B is predominated by cold water species and distributed mainly in the Arctic and subarctic seas with comparably low abundance and diversity. Cluster A is further divided into five subclusters, A1 to A5, which correspond to East China Sea, Philippine Sea, South China Sea, Sea of Japan, and Kuroshio Current, respectively; cluster B is divided into three subclusters, B1 to B3, which correspond to Sea of Okhotsk, Bering Sea, and subarctic gyre area, respectively. Based on the relationships between radiolarian faunas and major environment parameters in different biogeographic provinces, we suggest that the sea surface temperature (SST) and sea surface salinity (SSS) are primary factors that influence productivity, composition, and distribution pattern of the radiolarian fauna in the Northwest Pacific regions, while water depth is likely responsible for regional differences in the radiolarian fauna in each marginal sea. In addition, according to the distribution and abundance patterns of common radiolarian species in different areas, we identified five special radiolarian assemblages, which may be used as indicators for main Kuroshio Current, Kuroshio-East China Sea Branch, Kuroshio-South China Sea Branch, Tsushima Current, and Oyashio Current water masses
Compositions of foraminifera-rich turbidite sediments from the Shenhu area on the northern slope of the South China Sea: Implication for the presence of deep water bottom currents
No full textThe sediments in gravity core DH-1, collected from Shenhu area on the northern slope of the South China Sea, are composed of two dark grey clay silt layers (A(1) and A(3)) and two foraminifera-rich layers (A(2) and A(4)) (A(1) is the top layer and A(4) is the bottom layer). Major and trace metal contents, along with grain size and mineralogic data suggest that these silt layers represent background hemipelagic sedimentation. Unlike silt layers, the intervening foraminifera-rich layerA(4) exhibits a fining-upward trend, is distal turbidite. Grain size CM diagram and the sharp contacts between the foraminifera-rich layer A(2) and the upper and lower layers suggest layer A(2) is the result of depositional interaction between turbidite and bottom currents. AMS 14C dating of planktonic foraminifera indicate the age of the turbidite in A(2) is between15.3 ka and 22.6 ka. We hypothesize that turbidite formation in this period was related to the increase supply of terrigenous matter since the Last Glacial Maximum. The rapid deposition of each turbidite led to reduced rates of oxygen diffusion into the sediment, allowing anoxic conditions develop in sediments and fostering U enrichment (> 3.1 mu g/g) in foraminifera-rich layer A(4b). In contrast, decrease concentration of U and U/Mo ratios in foraminifera-rich layerA(2), which is possibly due to U remobilization as a consequence of downward penetration of the oxidation front from the oxygen rich bottom currents. These new data suggest that authigenic U was quite sensitive to the inflow of bottom currents, and U/Mo ratios may indicate the depositional environmental change in relation to the bottom current action on the turbidite. (C) 2017 Elsevier Ltd. All rights reserved
Cenozoic tectonic subsidence in the southern continental margin, South China Sea
No full textWe analyzed two recently acquired multi-channel seismic profiles across the Dangerous Grounds and the Reed Bank area in the South China Sea. Reconstruction of the tectonic subsidence shows that the southern continental margin can be divided into three stages with variable subsidence rate. A delay of tectonic subsidence existed in both areas after a break-up, which was likely related to the major mantle convection during seafloor spreading, that was triggered by the secondary mantle convection below the continental margin, in addition to the variation in lithospheric thickness. Meanwhile, the stage with delayed subsidence rate differed along strikes. In the Reed Bank area, this stage is between 32-23.8 Ma, while in the Dangerous Grounds, it was much later (between 19-15.5 Ma). We believe the propagated rifting in the South China Sea dominated the changes of this delayed subsidence rate stage
河台金矿是韧性剪切期形成的矿床?
No full text河台金矿位于广东省高要市境内,是目前粤西、桂东南已发现的最大的金矿田。河台金矿的金属量主要产出在高村、云西、后迳和河海矿段,已探明的储量包括金51.65吨(平均品位7.19 g/t),银7.58吨(平均品位7.19 g/t)和铜6.72吨(平均品位0.22%)。大地构造位置上,河台金矿位于钦杭结合带南段,罗定-广宁断裂与吴川-四会断裂的交汇部位。河台金矿主要赋矿地层为云开群上亚群,北侧和西北侧分别有印支期云楼岗和燕山期伍村花岗岩体侵入。云开群由一套整体无序的浅变质岩组成,局部遭受强烈韧性剪切
广州七星岗古海岸遗迹的发现及其科学意义
No full text文章论述吴尚时1937年发现并报道的广州东南郊七星岗海岸侵蚀地形及其附近松岗海积沙堤地形,论证吴尚时是珠江河口三角洲地区古海岸地形的首先发现者以及该古海岸地形形成于全新世中期全球海平面上升珠江河口发生桂州海进8―2 ka BP时段。指出七星岗古海岸地形的发现具有重要科学意义,表明中国学者的科研能力媲美同时代的洋学者,这一发现支撑了珠江三角洲的存在,同时为中国古籍对珠江河口湾演变的记述提供了实物证据,数十年来它在高等专业教学实习、科学研究、大众科学知识普及、社会文化教育中发挥了重要的作用,让多代地质、地理、海洋人才从中受益,并对珠江河口三角洲的整治与开发作出了很大的贡献。广州市政府1956年将七星岗古海岸遗址列为广州市重点文物,1983年广东省地理学会决定在该处建立纪念碑,近年建造七星岗古海岸遗址科学公园,这是对七星岗古海岸地形遗迹实施有效保护与发挥科教作用的绝佳举措。吴尚时重视野外考察,实事求是,不迷信、不盲从、善思考、勇探索、勤写作、贡献真知灼见的科学创新精神,值得我们学习
海底热液区蛇纹石化过程:生物作用vs.非生物作用
No full text海底热液区的发现备受地质学家、化学家和生物学家的关注。海底热液区主要分布于洋中脊和弧后盆地等构造环境中,可见细菌和古细菌等微生物以及虾、贝、螃蟹等大型生物的特殊生物群体。这些生物嗜热、嗜压、嗜酸或嗜碱。嗜热细菌和古细菌为热液区食物链的源头,以H_2和CH_4等物质为营养大量繁殖。H_2主要由裸露的地幔橄榄岩与海水发生蛇纹石化反应形成(1)
南海北部珠江口盆地惠州21-1油田CO_2-EOR与碳封存潜力快速评价
No full text广东省是二氧化碳(CO_2)排放大省,CO_2大型排放源集中于南海北部沿岸,与珠江口盆地大型油气田构造形成良好源汇匹配关系,因此,珠江口盆地油气田的CO_2驱提高采收率(EOR)和碳封存潜力与适宜性对于广东省低碳发展具有重要意义。采用UT快速评价模型,对珠江口盆地惠州21-1油田的主要油层开展了油层级别的CO_2-EOR和碳封存潜力初步评价,结果表明:(1)惠州21-1油田的6个主要油层中,M10与L60两个层具有最高的采收率(51%),其次为L40Up层(40%),这3个层的突破时间(tDo)也较短,驱油条件优于其他层。各层CO_2封存量(S_(CO2))约0.8PV(PV为孔隙体积),差别不大。结合油藏地质条件综合分析认为,M10层的CO_2-EOR和碳封存潜力将是各层中最高的。(2)参数敏感性分析表明,注入开始时含油饱和度(S_(oi))和注入压力(P_(inj))对采收率影响较大,变化幅度可达45%;tD0和S_(CO2)受Pinj影响较大,且S_(CO2)对于压力条件比tDo敏感;最小混相压力(PMM)对评价结果的影响呈非线性。因此,当油田S_(oi)和P_(MM)已确定时,要取得较好的采收率和CO_2封存效果,则主要通过适当提高注入压力来实现