Lake Qinghai sediment geochemistry linked to hydroclimate variability since the last glacial
Lake Qinghai sediment geochemistry linked to hydroclimate variability since the last glacial
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DOI：
10.1016/j.quascirev.2015.05.015
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发表时间：
2015-08
影响因子：
4
通讯作者：
Zhangdong Jin;Z. An;Jimin Yu;Fuchun Li;Fei Zhang
中科院分区：
文献类型：
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作者：
Zhangdong Jin;Z. An;Jimin Yu;Fuchun Li;Fei Zhang
半干旱区盆地沉积物的地球化学特征对了解过去的水文气候变化具有重要意义。本文研究了青海湖近32 ka沉积地球化学（Rb、Sr、Ca/Zr、TOC和%CaCO3）、碳酸盐矿物学和介形虫壳δ18O与沉积条件和水文气候变化的关系。青海湖位于北半球中纬度主要粉尘生产中心附近。湖相表层沉积物具有低rb、高Sr、低rb /Sr、高%CaCO3和高ca /Zr的化学特征，而风成黄土则具有高rb、低Sr、高rb /Sr、低%CaCO3和低ca /Zr的化学特征。短句来源青海湖两个短岩心的可溶性Ca和Sr含量与实测排水数据的直接对比表明，青海湖湖泊沉积物以Ca2+限制条件下形成的自生文石为主，文石的积累速率主要取决于雨季（5月下旬至9月）进入湖泊的溶质通量。我们的高分辨率下核记录显示，末次冰期（~ 32-19.8 ka）的沉积物具有高rb、低sr、低%CaCO3和低ca /Zr的特征，表明在干燥的冰川条件下，风沙（黄土）在干燥的盆地中积累，进一步得到了粒度和花粉结果的支持。这种类型的沉积在末次冰期（~ 19.8-11.5 ka）保持，但被具有高sr、高%CaCO3、高ca /Zr和低rb的幕式湖泊沉淀所中断。在~ 11.5 ka，沉积Rb/Sr、Ca/Zr、% caco3和TOC表现出剧烈而持久的变化，表明青海湖地区在全新世开始时发生了大气环流突变。湖相沉积在整个全新世持续存在，在全新世早期至中期（~ 10.5-8.0 ka）达到最大值。自~ 8.0 ka以来，文石和锶的逐渐显著减少与沙尘沉积的增加和介形虫δ18O的增加有关，这可能与全新世中后期亚洲夏季风的减弱有关。总体而言，青海湖沉积物发育和地球化学特征对末次冰期以来区域水文气候变化具有较高的敏感性。
Geochemistry of basin sediments from semi-arid regions is valuable to understand past hydroclimatic changes. Here, we investigate the links of sedimentary geochemistry (Rb, Sr, Ca/Zr, TOC, and %CaCO3), carbonate mineralogy and ostracod shell δ18O of Lake Qinghai, a basin proximal to major dust production centers at mid-latitudes of the Northern Hemisphere, to changes in depositional conditions and hydroclimate during the past 32 ka. Surface lacustrine sediments are characterized by low-Rb, high-Sr, low-Rb/Sr, high-%CaCO3and high-Ca/Zr values, in contrast to the chemical compositions of eolian loess (high-Rb, low-Sr, high-Rb/Sr, low-%CaCO3, and low-Ca/Zr). A direct comparison of soluble Ca and Sr in two short cores with instrumental water discharge data suggests that lacustrine precipitates in Lake Qinghai are dominated by authigenic aragonite formed under Ca2+-limited water conditions, and that the accumulation rate of aragonite dominantly depends on solute fluxes into the lake during the rainy seasons (late May to September). Our high-resolution down-core records show that sediments during the last glacial (∼32–19.8 ka) had high-Rb, low-Sr, low-%CaCO3, and low-Ca/Zr, indicating eolian dust (loess) accumulation in a desiccated basin under dry glacial conditions, further supported by grain size and pollen results. This type of sedimentation was maintained during the last deglacial (∼19.8–11.5 ka), but interrupted by episodic lacustrine precipitates with high-Sr, high-%CaCO3, high-Ca/Zr, and low-Rb. At ∼11.5 ka, sedimentary Rb/Sr, Ca/Zr, %CaCO3and TOC show dramatic and permanent changes, implying an abrupt shift in the atmospheric circulation at the onset of the Holocene in the Lake Qinghai region. Lacustrine precipitates have persisted throughout the Holocene with a maximum during the early to mid-Holocene (∼10.5–8.0 ka). Since ∼8.0 ka, the gradual and significant decreases in aragonite and Sr accumulations in tandem with increasing dust deposit and more positive ostracod δ18O may be linked to a weakening of Asian summer monsoons during the mid-to-late Holocene. Overall, our records appear to show a high sensitivity of sediment development and geochemistry in Lake Qinghai to the regional hydroclimate changes since the last glacial.