South Asian summer monsoon variability during the last ∼54 kyrs inferred from surface water salinity and river runoff proxies
South Asian summer monsoon variability during the last ∼54 kyrs inferred from surface water salinity and river runoff proxies
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DOI：
10.1016/j.quascirev.2016.02.012
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发表时间：
2016-04-15
影响因子：
4
通讯作者：
Frank, M.
中科院分区：
文献类型：
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作者：
Gebregiorgis, D.;Hathorne, E. C.;Frank, M.
南亚季风过去的变化主要是通过阿拉伯海的风力记录来了解的，而强季风降水地区的高分辨率古记录仍然缺乏。在这里，我们展示了从沉积岩芯 SK 168/GC-1 中获得的过去季风变化的记录，该岩芯是在安达曼海的阿尔科克海山复合体收集的。我们利用不同浮游有孔虫物种的生态栖息地，基于成对的 Mg/Ca 和 Delta O-18 分析重建淡水引起的分层，并估计海水 Delta O-18 (delta O-18(sw))。表面温度和温跃层温度 (Delta T) 和 Delta O-18(sw) (Delta delta 18O(sw)) 之间的差异用于研究上层海洋层化的变化。此外，G. sacculifer 测试中的 Ba/Ca 被用作与陆地季风降水相关的河流径流和海面盐度 (SSS) 变化的直接代理。我们的 Delta O-18(sw) 时间序列表明，上层海洋盐度分层在末次冰期期间没有显着变化，表明 NH 日照变化的影响很小。混合层和温跃层之间的温度梯度增加最强烈是在全新世中期记录的，表明存在明显较浅的温跃层。与之前的工作一致，三角洲 O-18(sw) 和 Ba/Ca 记录表明，末次盛冰期季风气候的特点是西南季风环流显着减弱，径流大幅减少。根据我们的数据，伊洛瓦底江上空的南亚夏季风（SAM）在末次盛冰期开始后逐渐加强，大约在 18ka 左右。这比阿拉伯海 Ba/Ca 记录增加约 3 公里，表明南亚季风气候动态比其他地区通常描述的 ITCZ 简单的南北位移更为复杂。全新世中期记录的最小 delta O-18(sw) 值与 Ba/Ca 同期，标志着季风降水较强，这与模型模拟一致。 (C) 2016 Elsevier Ltd. 保留所有权利。
The past variability of the South Asian Monsoon is mostly known from records of wind strength over the Arabian Sea while high-resolution paleorecords from regions of strong monsoon precipitation are still lacking. Here, we present records of past monsoon variability obtained from sediment core SK 168/GC-1, which was collected at the Alcock Seamount complex in the Andaman Sea. We utilize the ecological habitats of different planktic foraminiferal species to reconstruct freshwater-induced stratification based on paired Mg/Ca and delta O-18 analyses and to estimate seawater delta O-18 (delta O-18(sw)). The difference between surface and thermocline temperatures (Delta T) and delta O-18(sw) (Delta delta 18O(sw)) is used to investigate changes in upper ocean stratification. Additionally, Ba/Ca in G. sacculifer tests is used as a direct proxy for riverine runoff and sea surface salinity (SSS) changes related to monsoon precipitation on land. Our delta O-18(sw) time series reveals that upper ocean salinity stratification did not change significantly throughout the last glacial suggesting little influence of NH insolation changes. The strongest increase in temperature gradients between the mixed layer and the thermocline is recorded for the mid-Holocene and indicate the presence of a significantly shallower thermocline. In line with previous work, the delta O-18(sw) and Ba/Ca records demonstrate that monsoon climate during the LGM was characterized by a significantly weaker southwest monsoon circulation and strongly reduced runoff. Based on our data the South Asian Summer Monsoon (SAM) over the Irrawaddyy strengthened gradually after the LGM beginning at similar to 18 ka. This is some 3 kyrs before an increase of the Ba/Ca record from the Arabian Sea and indicates that South Asian Monsoon climate dynamics are more complex than the simple N-S displacement of the ITCZ as generally described for other regions. Minimum delta O-18(sw) values recorded during the mid-Holocene are in phase with Ba/Ca marking a stronger monsoon precipitation, which is consistent with model simulations. (C) 2016 Elsevier Ltd. All rights reserved.