|Place of Conferral||北京|
|Keyword||南黄海中部泥质沉积 中晚全新世 东亚冬季风 黄海暖流|
|Other Abstract|| 南黄海位于亚洲季风区，受季风影响显著。南黄海中部泥质沉积形成于全新世高海平面时期，受黄海暖流的影响较大。本文对南黄海中部泥质沉积区中心位置的Z1钻孔进行了AMS14C年龄、粒度、Uk’37-海水表层温度（SST）、TOC、TN和δ13Corg分析，综合指标 结果揭示了中晚全新世以来南黄海区域的东亚冬季风演化和海洋环境演化。|
6094 a B.P.以来，沉积速率、平均粒径和TOC/TN整体趋势的减少指示研究区陆源物质输入的减少，全新世中晚期东亚夏季风和东亚冬季风减弱从物源和物质搬运两个方面削弱了陆源物质的的输入。Z1岩芯还记录了两个高速沉积事件：6.1~5.7 ka B.P.高速沉积事件是该阶段冬季风较强促进海底沉积物再悬浮，沉积物搬运能力增强的结果；2.6~2.3 ka B.P.高速沉积事件则可能与3 ka B.P.左右黄海暖流达到现代水平，南黄海中部气旋式冷涡增强加速沉积有关。泥质沉积区的物质主要由黄海沿岸流搬运沉积，东亚冬季风强度控制沿岸流搬运的水动力条件，因此粒度参数变化可以反演东亚冬季风强度变化，结合TOC、TN含量、TOC/TN比值和δ13Corg变化将东亚冬季风的演化分为4个阶段：6.1~5.4 ka B.P.东亚冬季风强盛但较为稳定；5.4~3.9 ka B.P.东亚冬季风强盛但波动剧烈；3.9~2.0 ka B.P.东亚冬季风较弱且较为稳定；2.0~0 ka B.P.东亚冬季风较弱，但强度和波动略增。粒度、TOC、TN和TOC/TN指标还显示6 ka B.P.、5.3 ka B.P.、4.6 ka B.P.、4.0 ka B.P.和3.4 ka B.P.左右冬季风增强，这些事件与全球冷事件对应较好。
6094 a B.P.以来南黄海Uk’37-SST和δ13Corg呈低到高，不稳定到稳定的变化过程，且SST变化对全球/区域气候事件响应较好，记录了9次较为明显的降温事件，除了上面粒度指标记录的5次东亚冬季风增强事件以外，还有3100~2550 a B.P.、2450~2100 a B.P.、1500~750 a B.P.和750~250 a B.P.期间SST下降事件。整体趋势上将SST的变化分为3个阶段，6.1~3.9 a B.P. SST较低且波动较大，该阶段东亚冬季风强盛，黄海暖流开始入侵，海区温度变化受全球气候变化影响较大，SST在全球气候冷事件中下降幅度较大。3.9~2.0 ka B.P.期间SST逐渐上升且波动较大，此时冬季风较弱，黄海暖流开始增强，海海区温度变化主要还是受全球气候变化影响，但是黄海暖流对海区温度影响增加，SST在全球气候冷事件中下降幅度也较大；其中3100~2550 a B.P.期间SST下降在整个中晚全新世期间下降最为明显，就是受此阶段全球气候变冷和黄海暖流较弱共同导致；2450~2100 a B.P.冷事件在全球记录不完全一致，体现了气候变化的区域差异。2.1~0 ka B.P.期间SST保持在稳定高值但波动幅度减小，此时东亚冬季风很弱，黄海暖流强度接近现代水平，黄海暖流对海区温度变化影响很大；1500~750 a B.P.和750~250 a B.P.期间SST下降幅度小于前面两阶段的降温事件，可能原因是黄海暖流携带的暖水对全球气候变冷引发的SST下降起到一定的缓冲作用。
; The South Yellow Sea (YS) is an important marginal sea in the northwestern Pacific. Its environment and ecology have changed significantly during the Holocene. The changes in this area are influenced by the interactions of the Yellow Sea Warm Current (YSWC) and the East Asian Monsoon (EAM), which develops a typical circulation system at the center and forms a unique sediment body of fine particles, thereby concealing rich information on Paleoclimate and palaeoceanographic change, high-resolution records of the central mud in SYS are necessary. In this study, high-resolution multi-proxies records from a South Yellow Sea gravity core Z1 were achieved by analysis of AMS14C dating, grain size, Uk’37-sea surface temperature (SST) , TOC/TN and δ13Corg. Our results revealed the evolution history of the paleoenvironment in the South Yellow Sea muddy deposit as well as the variation of the Yellow Sea Warm Current since the mid Holocene.
EAWM broadly follows the orbital-derived insolation with a similar long-term step-decreased trend as the EASM since 6094 a B.P., which together results a decreased mass supply and material transportation into the SYS mud deposit. There were two high-sedimentation rate events: the intensified EAWM leads the increasing of terrigenous materials supply during 6.1~5.7 ka B.P. and 2.6~2.3 ka B.P., which was related to the strengthen of YSWC, the stabilizing of cyclone cold water mass of Yellow Sea might increase the deposition process.
The variation of grain size in core Z1 was closely related to resuspension and coastal currents due to the East Asian Winter Monsoon(EAWM) activity. Combined
with grain size parameters, the organic geochemistry proxies TOC, TN, C/N ratio and δ13Corg value could be used to indicate the input of terrigenous materials and/or the intensity of ocean primary productivity. Our result revealed the continuous history of EAWM over the past 6094 years could generally be divided into four periods: strong and stable during 6.1~5.4 ka B.P.; strong and highly fluctuation during 5.4~3.9 ka B.P.; weak and stable during 3.9~2.0 ka B.P.; and the transfer period during 2.0~0 ka B.P., when the intense of EAWM is increased and a little more fluctuation than during 3.9~2.0 ka B.P.. Correlation between regional records and global climate variations reveals that, the grain size was coarser at about 6.0 ka B.P., 5.3 ka B.P., 4.7 ka B.P., 3.9 ka B.P. and 3.4 ka B.P. corresponded well in time to strengthened EAWM.
The SST records could generally be divided into three stages: A low and highly fluctuation SST phase at 6.1~3.9 ka B.P.; A increasing and intensely fluctuating SST phase at 3.9~2.0 ka B.P.; and A high and lighter fluctuation SST phase since 2.0 ka B.P.. Variation of SST record corresponds well in time to nine global cold climate events. The former five cold events were the same with the strengthened EAWM events. The others occurred at 3100~2550 a B.P., 2450~2100 a B.P., 1500~750 a B.P. and 750~250 a B.P.. However, the amplitude of the SST response to cooling events was significantly different in different phases. The SST response to global cooling event was strong during 6.1~3.9 ka B.P. and the SST response was weak during 2.0~0 ka B.P.. The SST response to global cooling event was strongest during 3100~2550 a B.P., cause of little stronger EAWM and weak YSWC during the time. 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 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 EAWM and YSWC play important roles in the variation of SST.
Periodicity analysis shows the SYS give a good record of global high-frequency cycles including the millennial and centennial scale cycle reveals quite sensitive corresponds to the global and regional high-frequency climate events. Periods of record picked up from different proxies show similar periods, which reveal these paleo-environmental proxies have the same controlling factors. Centennial periodicities show that the solar activity has basic influences on SYS while the millennial periodicities show that the thermohaline circulation in the high latitude controls the paleoclimate change of the EAM.
|皮仲. 中全新世以来季风背景下黄海暖流的演化[D]. 北京. 中国科学院大学,2016.|
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