南海南部晚第三纪放射虫缺失事件及古海洋学意义

定量分析了南海南部ODP184航次1143站位12Ma以来沉积物中的放射虫.结果显示自晚中新世以来放射虫丰度有三个演化阶段,在时间上与西太平洋暖池的形成及盛衰变化很好的对应.其中5.96—3.3Ma放射虫缺失,硅藻也完全消失,但钙质生物的变化并不显著.这一放射虫缺失事件在时间上与巴拿马海道和印尼海道的关闭接近,故被认为是由于巴拿马海道和印尼海道的逐渐关闭,大洋环流重组,经历晚中新世的"生物勃发"时期,海水中营养大量消耗,同时期太平洋暖池减弱,东亚季风强度弱,影响到表层放射虫生产力.生物硅溶解作用及强烈的构造运动均对放射虫丰度产生了一定的影响.     

更新世南海南部上层海水结构变化的岁差驱动

ODP1143站浮游有孔虫次表层种Pulleniatina obliquiloculata与表层种Globigerinoides ruber的δ18O差值( Δδ18O(P-G))和δ13C的差值( Δδ13C(P-G))揭示了1.56?Ma以来南海南部温跃层和营养跃层冰期、间冰期的变化规律.有孔虫同位素差值与地球轨道参数ETP的交叉频谱揭示出岁差周期与更新世南海南部上层海水结构(温跃层和营养跃层)变化周期的相关性.在1143站Δδ18O(P-G)和Δδ13C(P-G)记录中也发现了丰富的半岁差周期.由于南海上层海水结构与东亚季风关系密切,岁差作为外部驱动力应对更新世东亚季风的变化产生重大影响.     

东经90°海岭远洋沉积物非碳酸盐组分的粒度特征及环境指示意义

对东经90°海岭北部ODP758站位远洋沉积物进行了粒度分析,得到了3.6 Ma以来非碳酸盐组分的粒度变化曲线,得出在3.6~2.8 Ma之间,非碳酸盐组分的粒度以2μm为主;2.8Ma至今,粒度增大至3μm左右,并且比较稳定地保持增大趋势的结论,这与南亚冬季风的爆发和加强密切相关。印证了青藏高原的隆升对亚州季风的影响。     

太平洋铁锰结壳中Sr含量变化:一个可能反映古气候变化的指标

铁锰结壳样品中Sr含量随时间的演化曲线与深部海水δ 18 O曲线具有相似变化趋势.尤其是1Ma以来,两者皆以约100ka的周期变化,与地球轨道偏心率的变化周期相符合.表明至少晚第四纪以来,铁锰结壳中Sr含量随时间演化曲线可以示踪古气候变化.影响铁锰结壳中Sr含量变化的几种因素:由间冰期向冰期转化,海平面下降引起近海区域的碳酸盐溶解、海水量减少导致海洋中Sr的含量升高、海洋表层生物生产率增加使表层海水中Sr随生物尸体向深部海水迁移、海洋中碳酸盐补偿深度变深导致深海碳酸盐沉积增加,这些因素综合作用的结果,使得冰期沉积的铁锰结壳Sr含量相对较高,间冰期沉积的铁锰结壳Sr含量相对较低.     

东经90°海岭远洋沉积物非碳酸盐组分的粒度特征及环境指示意义

对东经90°海岭北部ODP758站位远洋沉积物进行了粒度分析，得到了3．6Ma以来非碳酸盐组分的粒度变化曲线，得出在3．6～2．8Ma之间，非碳酸盐组分的粒度以2bLm为主；2．8Ma至今，粒度增大至3μm左右，并且比较稳定地保持增大趋势的结论，这与南亚冬季风的爆发和加强密切相关。印证了青藏高原的隆升对亚州季风的影响。     

珠江口盆地构造演化及对沉积环境的控制作用

通过对珠江口盆地沉积物地球化学成分分析表明,大洋钻探计划(ODP)1184站所揭示的主要构造沉积地层界线在珠江口盆地中亦同样存在,其元素在32,23.9,16Ma存在明显的突变,界线十分明显;这些陆源沉积物成分的变化是构造运动造成源区发生改变的直接证据.化学蚀变指数显示珠江口盆地在32,23.9,16Ma时期存在物理风化增强而化学风化减弱的突变事件,指示了由于构造运动造成母岩短时期内强烈快速的剥蚀作用,从而引起沉积物化学蚀变指数突然降低.根据元素相关性分析显示,ODP1148站沉积物与珠江口盆地沉积物亲缘关系密切,两者具有相同的物源.     

白云凹陷水道几何形态研究

以珠江口盆地白云凹陷中的水道为例,对水道的几何形态展开研究,通过均方根振幅属性图确定水道的整体
形态,截取若干横截面刻画水道的内部结构,并测量水道的深度和宽度,计算宽深比。研究发现,在该地区发育有两种
几何形态的水道,21.0∼18.5 Ma 时期水道变宽变浅和10.5∼8.5 Ma 时期水道变窄变深。水道的形态首先受到古地貌的
控制,21.0∼18.5 Ma 时期和10.5∼8.5 Ma 时期不同的地貌环境对两个时期水道的发育有重要的影响。此外,沉积流体
的侵蚀能力也影响了水道的形态。在21.0 Ma 时海平面上升,并且远离沉积物源会导致水道中的沉积物供给降低,流
体侵蚀能力较小,故水道变宽变浅。在10.5 Ma 时由于东沙隆起抬升的影响,并靠近物源使得水道中沉积物更多地以
重力流形式向下搬运沉积,侵蚀能力较强,故水道变窄变深。水道几何形态研究对研究水道的整体演化过程有重要意
义,也有助于了解该地区的沉积条件。     

宫古海峡典型断面水文特征分析

宫古海峡是连接东海与太平洋的重要水道,其水文要素变化与两者交换密切相关.文中基于海洋再分析数据集JCOPE2(Japan Coastal Ocean Predictability Experiments 2)的温度和盐度模拟结果,分析了宫古海峡典型断面(KR断面)温度、盐度、密度垂向分布的变化特征,讨论了密度跃层的季节分布和年际变化.结果表明:(1)KR断面温度在表层大于22,℃并随深度降低,1,000,m左右温度为4,℃;盐度(S)在次表层(100~200,m)达到最大(S34.85),在中层(500~800,m)最小(S34.30);表层密度低于22,kg/m3,随深度逐渐增加,1,000,m左右密度大于27,kg/m3.等密线与等温线分布基本一致,两者在黑潮核心区向下倾斜.(2)KR断面温跃层在126°E以东外海区季节变化分为4个阶段,分别为无跃期(1—4月)、成长期(5—6月)、强盛期(7—9月)和消衰期(10—12月),盐跃层则只存在于7—9月的陆坡处且厚度较薄,密度跃层变化与温跃层一致.(3)密度跃层的分布主要受控于温度,仅在126°E附近近表层海域受盐度影响.100,m以浅的海洋密度跃层总时间变化(年际变化与季节变化之和)明显大于中深层,而且黑潮流核处总时间变化明显小于其两侧.水体不同深度的密度跃层主要时间变化机制存在差异,200,m以浅季节变化显著,200,m以深年际变化显著.     

南极普里兹湾及邻近海域初级生产力的时空变异

在南大洋海冰区碳循环的研究中,初级生产力是最重要的基础数据之一.本文就中国南极科考第15、16航次的观测结果,着重讨论普里兹湾及邻近海域初级生产力(PP)的时空变异.第15、16航次生产力的平均测值分别为394.1和271.6 mgC·m-2·d-1,第16航次略低于第15航次.PP的空间分布呈湾内高,湾外低(陆坡、深海区最低)的特征.光合速率的垂直分布呈现次表层极大值型、随深度递减型和极小、极大迭加型3种分布特征,其分布受光照主控.初级生产力在短至1昼夜长达10年的时间尺度内均有显著的变化,初级生产力测值的年际变化最大达2.4倍.     

广西合浦廉州湾增养殖区水域营养水平分析与评价

根据2001～2003年广西沿海渔业生态环境调查监测数据,运用营养指数(E)法、有机污染指数(A)法以及初级生产力情况,分析与评价广西合浦廉州湾增养殖区水质不同时期营养水平时空分布特点、有机污染情况.结果显示该增养殖区水域营养水平指数E值时空变化范围为0.01～1.71;A值为-0.79～0.75;叶绿素a含量为0.31～2.83mg/m3.说明合浦廉州湾增养殖区水域营养水平总体上很低,处于贫营养状态,初级生产力水平低,但水域有机污染程度低,水质较好.     

Early Pleistocene formation of the asymmetric east-west pattern of upper water structure in the equatorial Pacific Ocean

Surface-and subsurface-dwelling planktonic foraminifera from the upper 43 m of Hole A at the Ocean Drilling Program (ODP) Site 807,which was recovered from the western Pacific warm pool during ODP Leg 130,were analyzed for stable oxygen and carbon isotopes.By comparing these results with data from ODP Site 851 in the eastern equatorial Pacific,this study has reconstructed the paleoceanographic changes in upper ocean waters in the equatorial Pacific since 2.5 Ma.During the period from 1.6-1.4 Ma,the oxygen isotopes of surface and subsurface waters were found to markedly change in the western and eastern equatorial Pacific,further confirming the final formation of the well-defined asymmetric east-west (E-W) pattern at that time.This feature was similar to the zonal temperature gradient (sea surface temperature is higher in the west and lower in the east) and the asymmetric upper water structure (thermocline depth is deeper in the west and shallower in the east) in the modern equatorial Pacific.The zonal gradient change of subsurface water δ18O was greater than that of surface water δ18O,indicating that the formation of the asymmetric E-W pattern in the equatorial Pacific should be much more related to the shoaled thermocline and markedly decreased subsurface water temperature in the eastern equatorial Pacific.Moreover,since ～1.6 Ma,the carbon isotopic differences between surface and subsurface waters clearly decreased in the equatorial Pacific,and their long-term eccentricity periods changed from 400 ka to ～500 ka,reflecting the reorganization of the ocean carbon reservoir.This probably resulted from the deep water reorganization in the Southern Ocean at that time and its enhanced influence on the tropical Pacific (especially subsurface water).Our study demonstrates that the tropical ocean plays an important role in global climate change.     

Benthic foraminiferal fauna turnover at 2.1 Ma in the northern South China Sea

Quantitative analysis of benthic foraminifera from ODP Site 1146 in the northern South China Sea (SCS) shows that abundance of Bulimina alazanensis, sometimes up to about 90%, decreased gradually since 3.2 Ma, especially at 2.1 Ma. Abundance of other benthic foraminiferal species, Globobulimina sub-globosa and Cibicidoides wuellerstorfi, increased after 2.1 Ma. Comparison with changes in oxygen and carbon isotopes of planktonic and benthic foraminifera shows that high abundance values of B. alazanensis corresponded with lower values of oxygen isotope, but for carbon isotope, high values of the species were consistent with heavier carbon isotope of benthic foraminifera and lighter carbon isotope of planktonic foraminifera, respectively, and vice versa. Considering factors such as uplift of Bashi Strait, expansion of the North Hemisphere Glaciation, strengthening of East Asian winter mon-soon and variations in oxygen and carbon isotope of foraminifera, changes of B. alazanensis in ODP Site 1146 suggest that the source of deep water masses of the northern South China Sea changed from the warm Pacific deep water with high oxygen content to Pacific Intermediate water with low oxygen content at 2.1 Ma. In addition, the strengthened East Asian winter monsoon resulted in increased pri-mary productivity, high nutrient and suboxic bottom water. Variations in species of B. alazanensis seemed to be unable to tolerate environmental stress induced by deep water masses and productivity changes.     

Pleistocene precession forcing of the upper ocean structure variations of the southern South China Sea

The precession plays a dominant role in driving the tropical monsoon variations. Our high resolution, millennial scale marine isotope records from ODP Site 1143 in the southern South China Sea (SCS) present the detailed history of the upper ocean structure variations over the past 1.56 Ma on glacial/interglacial timescale. The cross spectral analyses between the Earth's orbital variations and the isotopic differences reveal a high coherency between the East-Asian-monsoon-related thermocline and nutricline variations of the SCS and the precession. The variations of monsoon-related isotopic difference between species also demonstrate periodicities of 11-, 12- and 14- thousand years near semi-precession which originates in the tropics, highlighting the importance of the precession in driving the east Asian monsoon changes.     

Late Neogene radiolarian absence event in the southern South China Sea and its paleoceanographic implication

Down-core variations of radiolarians at ODP Site 1143 in the southern South China Sea （SCS） are presented for the last 12 Myr. The fluctuations of radiolarian abundances since the Late Miocene can be divided into three stages： a high abundance stage at 12-5.96 Myr, a radiolarian absent stage at 5.96-3.30 Myr and a gradual increasing stage after 3.30 Myr. The three stages correspond to the forming and vicissitudes of the Western Pacific Warm Pool （WPWP） and the Eastern Asian Summer Monsoon （EASM）. The radiolarian absence event （RAE） was also absent of diatom and occurred nearly simultaneously with the closures of the Panama Isthmus and the Indonesian seaway, which probably caused the reorganization of oceanic circulation systems. Accompanied this circulation reorganization was the weakening of the WPWP and the EASM, which probably led to a weakened upwelling in the southern SCS. In addition dissolved silica （Dsi） content in surface seawater might be very low during 5.96-3.30 Myr due to the ＂biogenic bloom＂ event, which consumed a large amount of Dsi in the surface seawater. All these factors together might lead to a great decrease of siliceous production in the southern SCS and consequently caused the RAE. Moreover, the dissolution of siliceous skeletons might also influence the abundance of radiolarians.     

Solar forced transient evolution of Pacific upper water thermal structure during the Holocene in an earth system model of intermediate complexity

Forced by transient solar activities since 7 ka,the thermal structures of the Pacific upper water at boreal winter are featured by an enhanced response of 3-dimensional Western Pacific Warm Pool(WPWP) in an Earth system model of Intermediate Complexity at centennial scales.During solar maximum periods,the magnitude of surface ocean temperature variations is 30% larger in the western tropical Pacific than in the Ni o3 region,while at subsurface,it is 40% larger in the subtropical North Pacific than in the western Equatorial Pacific.They compromise stronger zonal and meridional thermal gradients in surface and subsurface Pacific respectively which are both linearly responded to solar forcing at centennial periods.The surface gradient is most sensitive at 208-year period while the subsurface gradient shows more significance at periods longer than 208-year.Also noteworthy are two differences:(1) the phase lags at these periods of surface gradient are slightly smaller than that of subsurface;(2) the 148-year and 102-year periods in surface gradient are lost in subsurface gradient.These modeled features preliminary confirm the centennial fluctuations of WPWP in paleo-proxies and a potential solar forcing during the Holocene.     

热带西太平洋暖池对中国降水和沿海自然灾害的影响

用暖池指数研究了热带西太平洋暖池对中国降水和沿海自然灾害的影响。结果表明,暖池面积指数对中国降水有一定的预报意义,北界指数对中国长江中下游地区及其他一些地区的降水具有很好的预报性,面积指数与中国沿海台风次数的年际变化呈负相关关系,与1950年以后海冰灾害有明显的相关关系,与灾害性海浪的发生频数关系不大,与海啸的发生有一定的关系。     

Variations of opal accumulation rates and paleoproductivity over the past 12 Ma at ODP Site 1143, southern South China Sea

The biogenic silica analysis was performed on 463 samples from ODP 184 Site 1143, the southern South China Sea. The results show that the opal content and MAR evidently increased between 12.3 and 5.7 Ma, which was contemporary with the high carbonate and total MARs, reflecting the high biogenic productivity in the late Miocene.This demonstrates the occurrence of the late Miocene "Biogenie Bloom Event" in the southern South China Sea, corresponding to the late Miocene-early Pliocene "Biogenic Bloom Event" in the Indian-Pacific Ocean. The increases of opal content and MAR after the middle Pleistocene (about 0.7 Ma)is inferred to result from the enhanced upwelling and nutrient supply, which was induced by the intensified monsoon circulation after the "Mid-Pleistocene Revolution".     

太平洋暖池强化通量阵海域IFA气象要素的逐月变化

根据１９９２年１１月至１９９３年２月在太平洋暖池强化通量阵海域，四艘海洋调查船同步连续观测的气象资料，统计出该海域气温、海表温、气压和风和逐月变化。     

Exploring cyclic changes of the ocean carbon reservoir

A 5-Ma record from ODP Site 1143 has re-vealed the long-term cycles of 400—500 ka in the carbon isotope variations. The periodicity is correlatable all over the global ocean and hence indicative of low-frequency changes in the ocean carbon reservoir. As the same periodicity is also found in carbonate and eolian dust records in the tropical ocean, it may have been caused by such low-latitude proc-esses like monsoon. According to the Quaternary records from Site 1143 and elsewhere, major ice-sheet expansion and major transition in glacial cyclicity (such as the Mid-Brunhes Event and the Mid-Pleistocene Revolution ) were all pre-ceded by reorganization in the ocean carbon reservoir ex-pressed as an episode of carbon isotope maximum (d 13Cmax), implying the role of carbon cycling in modulating the glacial periodicity. The Quaternary glacial cycles, therefore, should no more be ascribed to the physical response to insolation changes at the Northern Hemisphere high latitudes alone; rather, they have been driven by the 揹ouble forcing? a combination of processes at both high and low latitudes, and of processes in both physical (ice-sheet) and biogeochemical (carbon cycling) realms. As the Earth is now passing through a new carbon isotope maximum, it is of vital impor-tance to understand the cyclic variations in the ocean carbon reservoir and its climate impact. The Pre-Quaternary varia-tions in carbon and oxygen isotopes are characterized by their co-variations at the 400-ka eccentricity band, but the response of d 13C and d 18O to orbital forcing in the Quater-nary became diverged with the growth of the Arctic ice-sheet. The present paper is the second summary report of ODP Leg 184 to the South China Sea.     

Evolution of the East Asian monsoon and its response to uplift of the Tibetan Plateau since 1.8 Ma recorded by major elements in sediments of the South China Sea

Evolution of the East Asian monsoon and its response to uplift of the Tibetan Plateau has been investigated in the study of global change. Core sediment samples drilled in the South China Sea during ODP Leg184 are the best materials for studying long-term variability of the East Asian monsoon. R-mode factor analysis of major elements in the fine grain-sized carbonate-free sediments (<4 μm) of the upper 185 mcd splice of ODP Site 1146 drilled during Leg184 in the South China Sea shows that Ti, TFe2O3, MgO, K2O, P, CaO, and Al2O3 are representative of a terrestrial factor. The variation in the terrestrial factor score is subject to chemical erosion in the source region and thus indicates the evolution of the East Asian summer monsoon. The terrestrial factor score has three stepwise decreases at ~1.3 Ma, ~0.9 Ma, and ~0.6 Ma, indicating the phased weakening of the East Asian summer monsoon is related to wholly stepwise, quick uplifts of the Tibetan Plateau since 1.8 Ma. The periodic fluctuation of the terrestrial factor score since ~0.6 Ma indicates that the glacial-interglacial cycles have been the main force driving the evolution of the East Asian monsoon. As in the case of Chinese loess, the long-term evolution of the East Asian monsoon recorded in sediments of the South China Sea reflects a coupled effect of the glacial-interglacial cycle and uplift of the Tibetan Plateau.