South Asian monsoon history over the past 60 kyr recorded by radiogenic isotopes and clay mineral assemblages in the Andaman Sea
South Asian monsoon history over the past 60 kyr recorded by radiogenic isotopes and clay mineral assemblages in the Andaman Sea
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DOI：
10.1002/2014gc005586
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发表时间：
2015-02-01
影响因子：
3.5
通讯作者：
Giosan, Liviu
中科院分区：
文献类型：
--
作者：
Ali, Sajid;Hathorne, Ed C.;Giosan, Liviu
南亚（或印度）季风的晚第四纪变率与冰期-间冰期和千年尺度的气候变化有关，但流入安达曼海的河流集水区过去的降雨强度仍然缺乏约束。本文利用安达曼海NGHP Site 17沉积物岩芯碎屑粘土粒度分数和粘土矿物组合的放射性成因Sr、Nd和Pb同位素组成，重建了过去60年间南亚季风的变化。在这段时间内，epsilon Nd值变化不大，通常在-7.3和-5.3之间振荡，Pb同位素特征基本不变，这与位于安达曼海东北方向的记录相反。这说明末次冰期和去冰期碎屑粘土的来源没有发生明显变化，表明季风在空间上是稳定的。最有可能的源头地区是伊洛瓦底江流域，包括印度-缅甸山脉，安达曼群岛可能有少量贡献。全新世的高蒙脱石/（伊利石+绿泥石）比值（高达14）和低Sr-87/Sr-86比值（0.711）表明，与海洋氧同位素第2和第3阶段相比，化学风化作用增强，南亚季风更强。较短的无蒙脱石间隔显示出明显的放射性成因Sr同位素组成，并记录了南亚季风的减弱，这可能与千年时间尺度上北大西洋的短期气候变率有关。
The Late Quaternary variability of the South Asian (or Indian) monsoon has been linked with glacial-interglacial and millennial scale climatic changes but past rainfall intensity in the river catchments draining into the Andaman Sea remains poorly constrained. Here we use radiogenic Sr, Nd, and Pb isotope compositions of the detrital clay-size fraction and clay mineral assemblages obtained from sediment core NGHP Site 17 in the Andaman Sea to reconstruct the variability of the South Asian monsoon during the past 60 kyr. Over this time interval epsilon Nd values changed little, generally oscillating between -7.3 and -5.3 and the Pb isotope signatures are essentially invariable, which is in contrast to a record located further northeast in the Andaman Sea. This indicates that the source of the detrital clays did not change significantly during the last glacial and deglaciation suggesting the monsoon was spatially stable. The most likely source region is the Irrawaddy river catchment including the Indo-Burman Ranges with a possible minor contribution from the Andaman Islands. High smectite/(illite+chlorite) ratios (up to 14), as well as low Sr-87/Sr-86 ratios (0.711) for the Holocene period indicate enhanced chemical weathering and a stronger South Asian monsoon compared to marine oxygen isotope stages 2 and 3. Short, smectite-poor intervals exhibit markedly radiogenic Sr isotope compositions and document weakening of the South Asian monsoon, which may have been linked to short-term northern Atlantic climate variability on millennial time scales.