Abstract 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 δ18Ocarb values 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 δ18Ocarb values. 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 δ18Ocarb variations. 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.

中文翻译：

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水深变化及其对碳酸盐含量和氧同位素的影响：过去7.6 kyr青海湖附近卫星湖的研究

摘要 沉积碳酸盐 (δ18Ocarb) 的氧同位素组成提供了湖泊系统中降水和蒸发之间区域水平衡的信息。提出了体积效应来解释在全新世早期观察到的高蒸发和低水位条件下青藏高原北部青海湖中异常低的 δ18Ocarb 值。体积效应理论指出，湖泊的小体积及其对淡水排放同位素信号的敏感性控制着 δ18Ocarb 值。在这项研究中，我们展示了来自青海湖附近一个小型咸卫星湖嘎海的碳酸盐含量和氧同位素的 7.6-kyr 记录。记录表明，嘎海湖的水位和湖泊大小在过去 7.6 kyr 发生了很大变化，并且体积效应是造成 δ18Ocarb 变化的原因。记录还表明碳酸盐沉淀对不同时间尺度的水深的不同反应。例如，在过去的 7.6 kyr 中，碳酸盐含量随着湖水位的增加而下降。这可以通过在低蒸发条件下逐渐淡水化以及青海湖和嘎海湖之间的联系增强来解释。然而，在百年尺度上，碳酸盐含量变化显着，与嘎海湖水位呈正相关。这种变化可能是由于湖水位周期性降低和陆地碎屑物质的影响更大，这导致了百年冷干期碳酸盐含量的稀释。所以，