Water depth variation and its impact on carbonate content and oxygen isotopes: A study from a satellite lake near Lake Qinghai over the past 7.6 kyr
Water depth variation and its impact on carbonate content and oxygen isotopes: A study from a satellite lake near Lake Qinghai over the past 7.6 kyr
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青海湖卫星湖近7.6 kyr水深变化及其对碳酸盐含量和氧同位素的影响
DOI：
10.1016/j.palaeo.2020.110150
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Min Wang
中科院分区：
文献类型：
--
作者：
Yunxin He;Xiangzhong Li;Yunning Cao;Jing Hu;Min Wang
沉积碳酸盐的氧同位素组成（δ 18 Ocarb）提供了湖泊系统中降水和蒸发之间区域水平衡的信息。青藏高原北方青海湖δ 18 O carb值在全新世早期高蒸发、低水位条件下异常偏低，可能是由于体积效应所致。体积效应理论认为，湖泊的小体积及其对淡水排放的同位素信号的敏感性控制了δ 18 Ocarb值。本文对青海湖附近的一个小的咸水卫星湖--青海湖的碳酸盐含量和氧同位素进行了7.6万年的记录。研究表明，在过去的7.6 kyr中，湖的水位和湖泊规模发生了很大的变化，体积效应是造成δ 18 Ocarb变化的主要原因。这些记录还表明，在不同的时间尺度上，碳酸盐沉淀对水深的反应截然不同。例如，在过去的7.6 kyr，碳酸盐含量随着湖泊水位的增加而减少。这是由于在低蒸发条件下，湖水逐渐变淡，青海湖与洱海之间的联系增强所致。百年尺度上碳酸盐含量变化显著，且与湖水位呈正相关。这种变化可能是由于周期性较低的湖泊水位和陆地碎屑物质的影响，这有助于稀释的碳酸盐含量在百年凉爽和干燥的时期。因此，为了提高我们对气候敏感地区过去水文气候变化的认识，应将不同时间尺度的信息分开。
The oxygen isotopic composition of sedimentary carbonate (δ18Ocarb) provides information on the regional water balance between precipitation and evaporation in a lacustrine system. A volume effect was proposed to explain the abnormally low δ18Ocarbvalues in Lake Qinghai on the northern Tibetan Plateau, under the conditions of high evaporation and low water levels, as observed during the early Holocene. Volume effect theory states that the small volume of the lake and its sensitivity to isotopic signals from freshwater discharge control the δ18Ocarbvalues. In this study, we present 7.6-kyr records of carbonate content and oxygen isotopes from Lake Gahai, a small and saline satellite lake near Lake Qinghai. The records demonstrate that the water level and lake size of Lake Gahai considerably changed over the past 7.6 kyr, and the volume effect was responsible for the δ18Ocarbvariations. The records also suggest contrasting responses of carbonate precipitation to water depth across different timescales. For example, over the past 7.6 kyr, the carbonate content decreased with increasing lake water levels. This can be explained by gradual water freshening under low evaporation conditions and enhanced connection between Lake Qinghai and Lake Gahai. On the centennial scale, however, the carbonate content varied significantly and was positively correlated with Lake Gahai's water level. Such a variation is probably due to the periodically lower lake water levels and a stronger influence of terrestrial clastic material, which contributed to the dilution of the carbonate content under centennial cool and dry periods. Therefore, in order to advance our understanding of past hydroclimatic variations in the climatically sensitive region, information across different timescales should be separated.