Formation and evolution of the modern warm current system in the East China Sea and the Yellow Sea since the last deglaciation

To reconstruct the formation and evolution process of the warm current system within the East China Sea (ECS) and the Yellow Sea (YS) since the last deglaciation, the paleoceangraphic records in core DGKS9603, core CSH1 and core YSDP102, which were retrieved from the mainstream of the Kuroshio Current (KC), the edge of the modern Tsushima Warm Current (TWC) and muddy region under cold waters accreted with the Yellow Sea Warm Current (YSWC) respectively, were synthetically analyzed. The results indicate that the formation and evolution of the modern warm current system in the ECS and the YS has been accompanied by the development of the KC and impulse rising of the sea level since the last deglaciation. The influence of the KC on the Okinawa Trough had enhanced since 16 cal kyr BP, and synchronously the modern TWC began to develop with the rising of sea level and finally formed at about 8.5 cal kyr BP. The KC had experienced two weakening process during the Heinrich event 1 and the Younger Drays event from 16 to 8.5 cal kyr BP. The period of 7-6 cal kyr BP was the strongest stage of the KC and the TWC since the last deglaciation. The YSWC has appeared at about 6.4 cal kyr BP. Thus, the warm current system of the ECS and the YS has ultimately formed. The weakness of the KC, indicated by the occurrence of Pulleniatina minimum event (PME) during the period from 5.3 to 2.8 cal kyr BP, caused the main stream of the TWC to shift eastward to the Pacific Ocean around about 3 cal kyr BP. The process resulted in the intruding of continent shelf cold water mass with rich nutrients. Synchronously, the strength of the YSWC was relatively weak and the related cold water body was active at the early-mid stage of its appearance against the PME background, which resulted in the quick formation of muddy deposit system in the southeastern YS. The strength of the warm current system in the ECS and the YS has enhanced evidently, and approached to the modern condition gradually since 3 cal kyr BP.

Sedimentary evolution since the late Last Deglaciation in the western North Yellow Sea

To decipher the sedimentary evolution and environmental changes since the late Last Deglaciation, two gravity cores were analyzed from the western North Yellow Sea (NYS). The two cores (B-L44 and B-U35) were sampled for grain size, clay minerals, detrital minerals, and 14C dating. They are comparable in lithofaies, and the observed succession was divided into four depositional units based on lithology and mineral assemblages, which recorded the postglacial transgression. Depositional unit 4 (DU 4) (before 11.5 ka) was characterized with enrichment in sand, and was interpreted as nearshore deposits in shallow water during the Younger Dryas Event. DU 3 (11.5-9.6 ka) displayed a fining-upward succession composed of sediments from local rivers, such as the Huanghe (Yellow) River, and from coastal erosion, which clearly were related to the Early Holocene transgression. Stable muddy deposition (DU 2) in NYS began to form at about 9.6 ka, which received direct supply of fine materials from the Shandong subaqueous clinoform. It is believed that the Yellow Sea circulation system played a major role in controlling the formation of fine sediment deposition in DU 1 (after 6.4 ka) after the sea level maximum.

Sedimentary Evolution of the Holocene Subaqueous Clinoform off the Southern Shandong Peninsula in the Western South Yellow Sea

Based on the stratigraphic sequence formed since the last glaciation and revealed by 3000 km long high-resolution shallow seismic profiles and the core QDZ03 acquired recently off the southern Shandong Peninsula, we addressed the sedimentary characteristics of a Holocene subaqueous clinoform in this paper. Integrated analyses were made on the core QDZ03, including sedimentary facies, sediment grain sizes, clay minerals, geochemistry, micro paleontology, and AMS 14 C dating. The result indicates that there exists a Holocene subaqueous clinoform, whose bottom boundary generally lies at 15–40 m below the present sea level with its depth contours roughly parallel to the coast and getting deeper seawards. The maximum thickness of the clinoform is up to 22.5 m on the coast side, and the thickness contours generally spread in a banded way along the coastline and becomes thinner towards the sea. At the mouths of some bays along the coast, the clinoform stretches in the shape of a fan and its thickness is evidently larger than that of the surrounding sediments. This clinoform came into being in the early Holocene(about 11.2 cal kyr BP) and can be divided into the lower and upper depositional units(DU 2 and DU 1, respectively). The unit DU 2, being usually less than 3 m in thickness and formed under a low sedimentation rate, is located between the bottom boundary and the Holocene maximum flooding surface(MFS), and represents the sediment of a post-glacial transgressive systems tract; whereas the unit DU 1, the main body of the clinoform, sits on the MFS, belonging to the sediment of a highstand systems tract from middle Holocene(about 7–6 cal kyr BP) to the present. The provenance of the clinoform differs from that of the typical sediments of the Yellow River and can be considered as the results of the joint contribution from both the Yellow River and the proximal coastal sediments of the Shandong Peninsula, as evidenced by the sediment geochemistry of the core. As is controlled mainly by coactions of multiple factors such as the Holocene sea-level changes, sediment supplies and coastal dynamic conditions, the development of the clinoform is genetically related with the synchronous clinoform or subaqueous deltas around the northeastern Shandong Peninsula and in the northern South Yellow Sea in the spatial distribution and sediment provenance, as previously reported, with all of them being formed from the initial stage of the Holocene up to the present.

Reconstruction of phytoplankton productivity and community structure in the South Yellow Sea

The sedimentary environment and ecological system in the South Yellow Sea (SYS) changed dramatically due to sea level change caused by glacial-interglacial cycles. The authors report the use of marine biomarkers (brassicasterol, dinosterol and C37 alkenones) and terrigenous biomarkers (C28+C30+C32 nalkanols) in core DLC70-3 from the SYS to reconstruct the variation in the phytoplankton productivity and community structure and possible mechanisms during the middle Pleistocene. The results show that the primary productivity and that of single algae presented a consistent trend for the whole core during the middle Pleistocene, which was high during interglacial periods and low during glacial periods, with the highest being in marine isotope stage (MIS) 5–9 and MIS 19–21. The main reason is that the Yellow Sea Warm Current (YSWC) carried much of high temperature, high salinity water into the SYS, causing upwelling and vertical mixing and stirring, which increased the nutrient supply in the photosynthetic layer. The phytoplankton community structure mainly showed an increase in the relative content of haptophytes in MIS 5–9 and MIS 19–21, while the relative content of diatoms and dinoflagellates decreased;there was no evidence for a haptophyte content in other stages. The results reveal a shift from a coccolitho-phoriddominated community during MIS 5 –9 and MIS 19 –21 to a diatom-dominated community during the other stages, mainly as a result of surface salinity variation, attributed to the invasion of the YSWC during high sea level periods.

Case analysis of water exchange between the Bohai and Yellow Seas in response to high winds in winter

Based on the data from a special project titled China's Offshore Marine Integrated Investigation and Evaluation as well as Regional Ocean Modeling Systems(ROMS)diagnostic numerical model,we studied the influence of high wind processes on the circulation and water exchange between the Bohai and Yellow Seas(BYS)in winter.The results show that the vertical structure of the Yellow Sea Warm Current(YSWC)is relatively uniform under condition of high winds,showing obvious barotropic features.However,this flow is not a stable mean flow,showing strong paroxysmal and reciprocating characteristics.A comparison of the changes in sea level suggests that the intensity of the northwards upwind flow is consistent with the abnormal fluctuations in the sea level.It indicates that the upwind flow is closely related to the water exchange between the BYS.The impact of high wind processes on the water exchange between the BYS is enormous.It can make the flux through the Bohai Strait,as well as that through the mouth of each constituent bay(i.e.,Liaodong Bay,Bohai Bay,and Laizhou Bay)far greater than usual,resulting in a significant increase in the water exchange rate.The exchange capacity,which is about 8%of the total volume of the Bohai Sea,can be completed in a few days.Therefore,the water exchange of the Bohai Sea may be completed by only a few occasional high wind processes in winter.

Sea surface temperature records of core ZY2 from the central mud area in the South Yellow Sea during last 6200 years and related effect of the Yellow Sea Warm Current

Sea surface temperature (SST) records in the South Yellow Sea during the last 6200 years are reconstructed by the unsaturation index of long-chain alkenones (K 37 U ') in sediment core ZY2 from the central mud area.The SST records varied between 14.1 and 16.5°C (15.6°C on average),with 3 phases:(1) A high SST phase at 6.2-5.9 cal ka BP;(2) A low and intensely fluctuating SST phase at 5.9-2.3 cal ka BP;and (3) A high and stable SST phase since 2.3 cal ka BP.Variation of the SST records is similar to intensity of the Kuroshio Current (KC),and corresponds well in time to global cold climate events.However,the amplitude of the SST response to cooling events was significantly different in different phases.The SST response to global cooling event was weak while the KC was strong;and the SST response was strong while the KC was weak.The difference in amplitude of the SST response is possibly caused by the modulation effect of the Yellow Sea Warm Current which acts as a shelf branch of the KC and a compensating current induced by the East Asia winter monsoon.The warm waters brought by the Yellow Sea Warm Current cushion the SST decrease induced by climate cooling,and both the Kuroshio and East Asian winter monsoon play important roles in the modulation mechanism.The SST records display a periodicity of 1482 years.The same period was found in the KC records,indicating that variation of the SST records in the central South Yellow Sea is strongly affected by KC intensity.The same period was also found in Greenland ice cores and North Atlantic and Arabian Sea sediment cores,showing a regional response of marine environmental variability in the East China Seas to that in the global oceans.

末次冰消期以来黄海海平面变化与黄海暖流的形成

ＹＳＤＰ１０２孔和ＹＳＤＰ１０３孔位于南黄海东南侧冷涡所对应的泥质沉积区，它们揭示了自末次冰消期以来的海侵沉积序列：海侵滞留沉积→潮流砂脊／潮坪～海滩沉积→陆架泥质沉积。该沉积序列上部的陆架泥质沉积厚度可达５０余米，在浅地震剖面上其内部存在一个明显的反射界面，从而将泥质沉积体分为上、下两个单元。泥质沉积体呈灰绿色调，含少量自生黄铁矿，但其内反射界面以上的沉积物含水量高。根据两个钻孔岩心中有孔虫的分布规律、泥质沉积层的化学组分、沉积磁组构特征以及现有测年数据，得到如下结论：（１）黄海暖流形成于大约６ｋａＢ．Ｐ．，（２）泥质沉积层内反射界面以上的沉积物是与黄海暖流伴生的冷涡沉积，（３）黄海地区末次冰消期海侵自略早于１４ｋａＢ．Ｐ．之前开始，至约６ｋａＢ．Ｐ．海平面达到最高位置。从６ｋａＢ．Ｐ．至今，海平面经历了几次波动，即在６～４ｋａＢ．Ｐ．和３～１．９ｋａＢ．Ｐ．海平面超过现今海平面位置；在４～３ｋａＢ．Ｐ．和１．９ｋａＢ．Ｐ．～现代，海平面有所降低，可能与现今海平面高度相当。

末次冰消期以来东黄海暖流系统的演化

以黑潮为主干的东黄海暖流系统，所携带的高温高盐水对我国近海的海洋环境和大气环流格局产生了重大影响。为系统重建由黑潮暖流、对马暖流和黄海暖流组成的东黄海暖流系统在末次冰消期以来的演化过程，建立末次冰消期以来东黄海暖流系统的演化模式，对取自黑潮主流轴附近的DGKS9603孔、现代对马暖流边缘的CSH1孔和与黄海暖流相伴生的冷水体下面的泥质沉积区YSDP102孔的古海洋记录进行综合分析研究。结果表明，现代东黄海暖流系统是伴随着末次冰消期以来黑潮的演化和海平面的脉冲式上升而形成与演化的，地理边界条件是非常重要的控制因素。16kaB．P．黑潮对冲绳海槽的影响开始加强，之后随着海平面的上升，对马暖流开始发育，到8．5kaB．P．左右，现代对马暖流正式形成，期间黑潮暖流经历了Heinrich 1和Younger Dryas事件的两次减弱过程。7—6kaB．P．是黑潮暖流和对马暖流末次冰消期以来最强盛的时期；约6．4kaB．P．左右黄海暖流开始出现，至此东黄海暖流系统的基本格局已完全形成；在5．3—2．8kaB．P．期间，冲绳海槽发生了以“Pulleniatina低值事件”为标志的黑潮变弱过程，导致对马暖流主流轴在3kaB．P．左右发生了一次向太平洋方向的偏转事件，低温、高营养物质含量的陆架冷水团对冲绳海槽北部影响加强，期间在黄海暖流附近冷水体下面堆积了巨厚的泥质沉积体系。此后，由黑潮暖流、对马暖流和黄海暖流组成的东黄海暖流系统显著加强，直至达到现代的态势。

冰消期海侵进程中南黄海潮流沙脊的演化模式

南黄海东侧底形资料、浅地层剖面和 YSDP- 10 2钻孔揭示了冰消期海侵初期的古潮流沙脊群 ;南黄海QC2孔上部岩心又揭示了全新世中期的埋藏古潮流沙脊群 ;842 2柱状岩心补充了若干现代南黄海沙脊群——苏北岸外辐射状沙脊群的特征。根据 1 4 C测年、ESR测年及突变事件的分析 ,获得了不同时期沙脊形成的年代标尺 ,并获得以下结论 :(1)沙脊沉积在层序地层中属上海侵体系域 (U TST) ,其发育与海平面密切相关 ,最佳发育深度在- 2 0～ - 30 m水深范围内 ,很少有超过 - 40 m者。南黄海沙脊群随着陆架海侵进程自东向西跃迁 ,沙脊群广泛发育预示海平面的相对稳定或小幅度波动期 ;海平面急剧上升期实现了沙脊群的跃迁。南黄海沙脊演化可划分为 3期 :早期 (约 12～ 9ka)是据新仙女木期 (YD)的海平面波动 ,以南黄海东侧古潮流沙脊群为代表 ;中期 (约 6 .3～4ka)包括了中全新世高温期气候突然衰退事件 (MHCR)的海平面波动 ,南黄海中部 QC2孔揭露的埋藏潮流沙脊是这一期的代表 ;晚期为 2 ka至今的海平面缓慢波动期 ,以现代苏北岸外辐射沙脊群为代表。 (2 )潮流沙脊沉积物特征反映了水动力条件的变化。早期沙脊处于强动力作用下 ,随着海侵范围扩大 ,形成沙脊的动力条件愈来愈弱。(3)南黄海、东海与北黄海沙脊发育与演化?

黄海中部泥质区底栖有孔虫群落对早全新世海平面快速上升的响应

末次冰消期以来全球海平面经历了很大变动,本文通过陆架泥质区资料,对黄海中部泥质区5个沉积物柱样进行了AMS 14C年代测试,结合沉积物粒度组成与底栖有孔虫资料探讨黄海中部泥质区底栖有孔虫对早全新世海平面快速上升的响应。结果表明,约13.0 ka以来底栖有孔虫群落对海平面变化的响应呈现明显的3个阶段:早期阶段(约13.0~10.0 ka期间),底栖有孔虫以近岸浅水组合为主,与这一时期海平面相对较低对应,泥质区整体呈滨岸环境,水动力环境较强,有机质等食物供给相对丰富,底栖有孔虫丰度相对较高;中期阶段(约10.0~7.0 ka期间),底栖有孔虫群落几乎消失,可能是由于海平面快速上升,动荡的海洋环境不利于有机质沉降,造成底栖有孔虫食物供给不稳定,不利于底栖有孔虫生存所致;晚期阶段(约7.0 ka以来),底栖有孔虫群落逐渐繁盛,以黄海中部冷水团特征组合为主,反映了区域海平面相对稳定、泥质沉积的形成以及黄海冷水团核心区域的出现等海洋环境变化为底栖有孔虫带来了稳定的有机质供给,故而底栖有孔虫丰度迅速增加到与现在相当的水平。黄海中部泥质区多柱样底栖有孔虫群落变化对早全新世海平面上升有较一致的响应,为该区全新世早期海平面快速上升以及黄海现代环流体系的形成提供了更直接的证据。