Glacial-interglacial contrast in MBT/CBT proxies in the South China Sea: Implications for marine production of branched GDGTs and continental teleconnection
Glacial-interglacial contrast in MBT/CBT proxies in the South China Sea: Implications for marine production of branched GDGTs and continental teleconnection
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DOI：
10.1016/j.orggeochem.2014.12.008
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发表时间：
2015-02-01
影响因子：
3
通讯作者：
Zhang, Chuanlun L.
中科院分区：
文献类型：
--
作者：
Dong, Liang;Li, Qianyu;Zhang, Chuanlun L.
支链甘油二烷基甘油四醚(BR GDGTS)的甲基化指数(MBT)和环化比(CBT)这两个支链甘油二烷基甘油四醚(BR GDGTS)指标常被用来重建古平均年气温(MAAT)和土壤pH，前提是海洋环境中BR GDGTS主要来自陆源。然而，越来越多的证据表明，br GDGT可以在海洋环境中就地产生，这可能会影响MAAT的重建和其他相关古环境指标的使用。我们在南中国海南部的一个沉积岩芯(MD052896/7)中确定了br GDGT分布，提供了MBT和CBT指数以及分支和类异戊二烯四醚(BIT)指数的高分辨率剖面。间冰期(MIS1和MIS5)的BIT值远低于冰期(MIS2，MIS3，MIS4和MIS6)。另一方面，MBT/CBT得到的温度在间冰期显示较低的值，但在冰期显示较高的值。我们假设，间冰期较低的MBT/CBT派生温度反映了海洋条件下产生的br GDGT所记录的底层水温，而冰期较高的MBT/CBT派生温度反映了陆地MAAT，因为当海平面较低时，来自陆地的br GDGT输入过多。同样，CBT得出的土壤pH似乎被间冰期海洋BR GDGT的产量所覆盖，但对冰期陆地降水的响应，表现出类似于或作为对遥相关引起的南半球气候振荡的积极响应。结果表明，受冰期-间冰期旋回的制约，南中国海MBT/CBT的变化呈现出前所未有的格局。在这种约束下，MBT/CBT揭示了间冰期br GDGT的深水生产，并记录了冰期陆地古水文的变化，为利用有机替代物研究古气候提供了新的视角。(C)2014爱思唯尔有限公司。保留所有权利。
Two proxies derived from branched glycerol dialkyl glycerol tetraethers (br GDGTs), the methylation index of branched tetraethers (MBT) and the cyclization ratio of branched tetraethers (CBT), are often used to reconstruct paleo mean annual air temperature (MAAT) and soil pH based on the premise that br GDGTs in the marine environment are mainly of terrigenous origin. However, mounting evidence indicates that br GDGTs can be produced in situ in oceanic settings, which may affect MAAT reconstruction and the use of other related paleoenvironmental proxies. We have determined br GDGT distributions in a sedimentary core (MD05-2896/7) from the southern South China Sea, which provided high resolution profiles of MBT and CBT indices as well as the branched and isoprenoid tetraether (BIT) index. BIT varied systematically with glacial-interglacial cycles, reaching much lower (< 0.1) values during the interglacial periods (MIS 1 and MIS 5) than during the glacial periods (MIS 2, MIS 3, MIS 4 and MIS 6). MBT/CBT-derived temperature showed, on the other hand, lower values during the interglacial periods but higher values during glacial periods. We hypothesize that the lower MBT/CBT-derived temperature during interglacial periods reflects bottom water temperature registered via br GDGTs produced under marine conditions, whereas the higher MBT/CBT derived temperature during glacial periods reflects terrestrial MAAT because of the overwhelming input of br GDGTs from land when the sea level was low. Similarly, the CBT-derived soil pH appeared to have been overprinted by marine br GDGT production during interglacial periods but responded to precipitation on land during glacial periods, showing patterns similar to, or as a positive response to, the southern hemispheric climate oscillation due to teleconnection. Our results demonstrate an unprecedented pattern of MBT/CBT variation constrained by glacial-interglacial cycles in the South China Sea. Under this constraint, MBT/CBT revealed deep water production of br GDGTs during interglacial periods and recorded changes in paleohydrology on land during glacial periods, providing a new perspective for paleoclimate studies using organic proxies. (C) 2014 Elsevier Ltd. All rights reserved.