东海内陆架EC2005孔沉积物磁化率与粒度组分的相关性研究

对位于浙-闽沿岸泥质带的EC2005孔长岩芯(6 020 cm)进行了磁化率和粒度测量,分析了沉积物不同粒级组分和磁化率大小变化的相关关系.通过计算两者的相关系数,认为在整段岩芯上两者呈正相关,且磁性颗粒主要赋存在粗颗粒物质中.磁化率与>63 μm的组分含量的相关系数为0.510,而对<4 μm乃至<16 μm的组分,与磁化率呈反相关,相关系数可达-0.644.在不同沉积相中,磁化率和不同粒度组分含量的相关关系有所不同.前三角洲相和前滨相沉积物的磁化率和粒度组分没有表现出明显的相关性;三角洲前缘相和三角洲平原相沉积物磁化率和粒度的相关性与整段岩芯的相似;浅海相沉积物4～16 μm的组分与磁化率呈较强的反相关.600～2 806 cm的沉积物可能遭受了早期还原成岩作用,导致磁化率与粒度组分的相关程度降低.水动力条件是影响两者相关性的重要因素.水动力条件强,则两者相关性较好;水动力条件较弱,则两者基本不相关.磁化率和粒度组分的相关性还受到物源变化、分选程度的影响.磁化率和粒度的组合特征蕴含了一定的古气候信息.全球性的气候事件如新仙女木事件、8-2 ka冷事件在粒度参数中都有较好的响应,相比之下磁化率数据的变化幅度没有粒度数据强烈,可能与磁化率的多种控制因素有关.     

东海陆架北部长江、黄河沉积物影响范围的定量估算

采用粒度分析、扫描电镜观察（SEM）、ICP－AES分析等方法，得到了关于长江、黄河入海沉积物的示踪粒级以及示踪指标，并提出沉积物物源定量识别的非线性规划数学模型，进而实现了东海陆架北部表层沉积物中长江型、黄河型物质的定量估算。     

东海陆架北部泥质区沉积动力过程的季节性变化

利用东海陆架北部泥质区（济州岛西南）及其周围不同季节５个航次的悬浮体资料和相应的底质粒度资料,对该泥质区沉积动力过程的季节性变化规律进行了分析。结果表明：东海陆架北部悬浮体的高含量区并不与该区的沉积中心（泥质区）相吻合,泥质区的形成需有物源的充沛供应和涡旋的动力效应相结合。泥质区沉积作用时空变化具有强烈的季节性。冬季泥质区悬浮体供应充足,涡旋中心向泥质区东南扩展,是本区接受悬浮体沉积的关键季节。夏     

末次冰期以来东海内陆架沉积反映的海平面变化

对东海内陆架泥质沉积区MD06-3042孔(27°05.4′N,121°24.1′E,水深62m,岩芯长34.1m)样品进行了高分辨率的粒度分析和14C年代测试,重建了末次冰期以来东海内陆架区的海平面及沉积环境的变化.14.0ka左右,海平面已经到达现今海平面下62m等深线的位置,大量沉积物在此沉积.13.0~4.2ka之间,受海流等多种因素影响,少量沉积物在此沉积.4.2~3.2ka之间,现代东海内陆架的泥质沉积主体在该岩芯附近快速堆积.东海内陆架的泥质沉积体由北向南,由内向外逐渐形成,具有阶段性.     

东海内陆架泥质沉积Rb和Sr的地球化学及其古气候意义

通过对位于东海内陆架闽浙沿岸泥质沉积区北部的DD2孔进行AMS14C年龄测试和Rb,Sr含量测定,获得了近2ka的Rb/Sr比值(RRb/Sr)变化的高分辨率曲线。该曲线揭示出10次RRb/Sr低值时期,它们与历史时期中国温度下降有很好的对应关系,并印证了约990AD的降温事件。根据RRb/Sr的变化,基本认同竺可桢所界定的隋唐温暖期,并认为气候存在温暖-寒冷-温暖的波动,且其中的相对寒冷期为800-890AD。研究认为小冰期时间段为1480-1890AD,且由3个寒冷阶段构成,小冰期的最冷峰为约1520AD,1670AD,1780AD和1850AD。     

东海陆架北部表层细粒级沉积物的级配及意义

本文依据东海陆架北部23个表层沉积物样品的粒度分析资料，就东海陆架北部表层细粒级沉积物的级配及意义进行了研究。结果表明，研究区表层沉积物中细粒级部分以＜0．016mm为优势粒级，可占到总细粒级沉积物的75％以上。济州岛西南泥质区以细于0．008mm粒级的沉积物占据优势，长江口泥质区则以＜0．016mm粒级的沉积物为主，两泥质区细粒级沉积物的级配很不相同。     

中国边缘海陆源沉积物粒度与矿物组成的关系

尝试建立了中国边缘海陆源沉积物粒度和矿物成分的关系．对东海内陆架EC2005孔和南海ODP1146站沉积物进行了陆源物质粒度以及矿物分析,EC2005孔矿物分析采用X射线衍射方法,ODP1146站则采用化学分离单矿物方法．二者主要矿物成分均为石英、长石以及黏土矿物,黏土矿物主要赋存于细粒组分,而石英、长石矿物则主要赋存于较粗粒级中,石英＋长石含量与陆源物质粒度的大小均表现出正相关,EC2005孔较之南海ODP1146站平均粒径与石英＋长石含量相关性偏低,体现了在不同海区二者具有不同的相关关系．建立了中国边缘海陆源物质平均粒径与主要矿物成分含量大小的函数模型,提出在邻近研究区可以据此对后者进行预测,也可以为今后的世界其他海区沉积学、矿物学研究提供参考．     

从陆架泥质沉积中寻找高分辨率的全新世东亚季风记录

当前对全新世东亚季风的研究,一是重造了不同地区的季风气候与环境特点,分析、划分了不同的阶段并总结了各阶段的特点;二是通过高分辨率的气候代用指标进一步开展定量古气候研究,揭示其变化与周期,探讨其驱动机制.已有的研究主要来自陆地,而利用海洋沉积物研究季风则集中在深海;且主要体现的是气候整体变化特征或侧重于夏季风,而专门论述全新世东亚冬季风的报道则较少;尚未在短时间尺度上有效地确定全新世东亚冬、夏季风的关系及其驱动机制.该文指出,可以利用中国边缘海陆架泥质沉积开展全新世高分辨率的东亚古季风研究,其粒度和Rb/Sr比值等元素地球化学指标可分别作为高分辨率的东亚冬、夏季风演化的替代性指标.     

近8 ka东亚冬季风记录在东海内陆架的建立

目的在于尝试从东海内陆架上建立全新世高分辨率的东亚冬季风替代性序列.通过对位于东海内陆架闽浙沿岸泥质中部的PC-6孔(740 cm)进行AMS14C年龄测试和粒度分析,综合沉积构造、沉积层序与海平面变化讨论该孔的沉积环境,其上(0~450 cm)、中(450~540 cm)、下(540~740 cm)段分别对应于前滨、近滨和与现今环境基本一致的浅海沉积环境,其中上段的沉积作用主要受控于东海冬季沿岸流.通过计算该孔的粒级-标准偏差,提取了环境敏感粒度组分,该孔沉积物粒度由以28μm为界的2个粒度子体构成,它们的峰值即约5~6μm与102~125μm分别为对应于冬季沿岸流和波浪的敏感粒级;细粒组分(<28μm)对应于沿岸流,为沿岸流所携带,表现为平行于海岸的横向迁移,粗粒组分对应于波浪,沉积物以垂直于海岸的纵向迁移为主.PC-6孔上段细粒组分的含量一般在85%以上,利用其平均粒径序列建立了研究东亚冬季风演化的替代性序列.     

Records of the East Asian winter monsoon from the mud area on the inner shelf of the East China Sea since the mid-Holocene

AMS¹⁴C dating and analysis of grain size, major elements and clay minerals were applied to Core MZ01 from the mud area on the inner shelf of the East China Sea. Based on the environmentally sensitive grain size, clay mineral and major element assemblages, the history of the East Asia winter monsoon since the mid-Holocene could be reconstructed. These three proxies, mean grain size (>9.71 μm), chemical index of alteration (CIA) and ratio of smectite to kaolinite in particular, show similar fluctuation patterns. Furthermore, 10 extreme values corresponding to the contemporary cooling events could be recognized since the mid-Holocene; these extreme values are likely to have been caused by the strengthening of the East Asia winter monsoon. The cooling events correlated well with the results of the δ¹⁸O curves of the Dunde ice core and GISP2, which therefore revealed a regional response to global climate change. Four stages of the East Asia winter monsoon were identified, i.e. 8300–6300 a BP, strong and unstable; 6300–3800 a BP, strong but stable; 3800–1400 a BP, weak and unstable; after 1400 a BP, weak but stable.     

Recent 2000-year geological records of mud in the inner shelf of the East China Sea and their climatic implications

AMS^14C dating and grain-size analysis for Core DD2, located at the north of the Yangtze River-derived mud off the Zhejiang-Fujian coasts in the inner shelf of the East China Sea, provide us a high-resolution grain-size distribution curve varying with depth and time. Data in the upper mud layer of Core DD2 indicate that there are at least 9 abrupt grain-size increasing in recent 2000 years, with each corresponding very well with the low-temperature events in Chinese history, which might result from the periodical strengthening of the East Asian Winter Monsoon (EAWM), including the first-revealed maximum temperature lowering event at around 990 a BP. At the same time, the finer grain size section in Core DD2 agrees well with the Sui-Tang Warming Period (600--1000 a AD) defined previously by Zhu Kezhen, during which the climate had a warm, cold and warm fluctuation, with a dominated cooling period of 750-850 a AD. The Little Ice Age (LIA) can also be identified in the core. It starts around 1450 a AD and was followed by a subsequent cooling events at 1510, 1670 and 1840 a AD. Timing of these cold events revealed here still needs to be further verified owing to some current uncertainty of dating we used in this study.     

Preservation of black carbon in the shelf sediments of the East China Sea

Concentrations and carbon isotopic(14C,13C) compositions of black carbon(BC) were measured for three sediment cores collected from the Changjiang River estuary and the shelf of the East China Sea. BC concentrations ranged from 0.02 to 0.14 mg/g(dry weight) ,and accounted for 5% to 26% of the sedimentary total organic carbon(TOC) pool. Among the three sediment cores collected at each site,sediment from the Changjiang River estuary had relatively high BC contents compared with the sedi-ments from the East China Sea shelf,suggesting that the Changjiang River discharge played an im-portant role in the delivery of BC to the coastal region. Radiocarbon measurements indicate that the ages of BC are in the range of 6910 to 12250 years old B.P.(before present) ,that is in general,3700 to 9000 years older than the 14C ages of TOC in the sediments. These variable radiocarbon ages suggest that the BC preserved in the sediments was derived from the products of both biomass fire and fossil fuel combustion,as well as from ancient rock weathering. Based on an isotopic mass balance model,we calculated that fossil fuel combustion contributed most(60%―80%) of the BC preserved in these sediments and varied with depth and locations. The deposition and burial of this "slow-cycling" BC in the sediments of the East China Sea shelf represent a significant pool of carbon sink and could greatly influence carbon cycling in the region.     

Observation of small-scale processes over shelf break in the East China Sea

The turbulent dissipation along with temperature and salinity was measured on board R/V Dong Fang Hong 2 over the shelf break of the East China Sea from March 7 to 9, 2004. Applying the Turner angle, it is found that the ＇diffusive＇ double diffusion, salt-fingering, and stable stratification coexist in the upper water column of about 50 m. Below that depth, there exists weak salt-fingering. The turbulent dissipation rates are enhanced along the ray paths of M2 internal tides emanating from the shelf break with values ranging from 1.0×10^-9 W·kg^-1 to 1.2×10^-6 W·kg^-1. The corresponding diapycnal mixing rates are from 1×10^-6 m^2· s^-1 to 1×10^-2 m^2· s^-1. The spatially averaged mixing rate over the whole observation section is 2.3×10^-3 m^2· s^-1, which is much larger than 1×10^-5 m^2·s^-1 of the background diapycnal mixing rate in the open ocean.     

Linear sand ridges on the outer shelf of the East China Sea

Based on the latest full-coverage high-resolution multi-beam sounding data, the distribution of the linear sand ridges on the outer shelf of the East China Sea （ECS） is studied with quantitative statistical analysis. The study area can be divided into the northeastern part and the southwestern part. Sand ridges in the northeastern area, trending 116°N, show obvious linear character and shrink to the inner shell Sand ridges in the southwestern area, trending 120°N -146°N, tend to have net form. Sand ridges gradually become sand sheets in the center part of study area. Sand ridges are distributed landward to the isobath of 60m, distributed seaward to the water depth of 120 m in the northeast and 150 m in the southwest. Immature sand ridges are observed at water depth of 130-180 m in the southwestern depressions. The acoustic reflection properties of the internal high.angle inclined beddings of the sand ridges are analyzed based on the typical seismic profiles close to the research area. Lithological analysis and dating of 4 boreholes and 12 cores indicate that the widely distributed transgressive sand layer with high content of shell debris which was formed in the early-middle Holocene is the main composition of the linear sand ridges on the outer shelf of the ECS. The dominating factor in formation, developing and burying of the sand ridges is the variation of water depth caused by sealevel change and the rate of sediment supply. In 12400 aBP the cotidal lines of the M2 tidal component were closely perpendicular to the strike-directions of the sand ridges in the study area, and the tidal wave system during 12000-8000 aBP might play a key role in the formation of the linear sand ridges which are widely distributed on the outer shelf of the ECS.     

Sea surface temperature record from the north of the East China Sea since late Holocene

Using the alkenone paleotemperature index U37^k, a high-resolution sea surface temperature （SST） record since 3600 a BP was reconstructed from the mud area in the north of the East China Sea. Combining with the grain size distribution curve of sensitive grain size group, which may reflect the East Asia Winter Monsoon activity, the palaeoenvironmental evolution cycle throughout the late Holocene in the area was obtained. The marine environment evolution during the last 3600 years displays a five-stage trend. （1） Temperature descending period from 0.85 cal. ka BP to present. The maximum temperature decrease amplitude is 2℃. The winter monsoon intensified and ＇Little Ice Age＇ were recorded in this period. （2） Warming period from 1.90 to 0.85 cal. ka BP. The mean temperature increase amplitude is 0.8℃. The Sui-Tang warming period was recorded at about 0.85--1.35 cal. ka BP and a prominent cooling event was recorded at 1.4 cal. ka BP in this period. （3） Temperature descending period from 2.55 to 1.90 cal. ka BP. Temperature cooling amplitude is 0.9℃. This period is coincident with an integrated temperature circle recorded in the Antarctic ice core, with the temperature changes from a slow cooling stage to a rapid warming stage. （4） Temperature comparatively stable with a little ascending period from 3.2 to 2.55 cal. ka BP. Temperature warming amplitude is 0.3℃. This period is coincident with the temperature fluctuant ascending period recorded in Antarctic ice core. （5） Temperature comparatively stable with little descending period from 3.6 to 3.2 cal. ka BP. This period corresponds with the temperature fluctuant cooling period recorded in Antarctic ice core. Basically, those five periods were coincident with the Antarctic ice core record. During the global cooling stage, the SST change in the continental shelf sea can be adjusted simultaneously.