The scarcity of modern process studies of the relationship between climatic variables and lake-water oxygen isotope (δ18OLW) composition has restricted our understanding of the climatic significance of oxygen isotope (δ18O) records from lake sediments. We measured changes in δ18OLW at four lakes (Nanyihu, Gonghai, Mayinghai and Xihaizi) at various locations across the East Asian summer monsoon (EASM) region, from December 2016 to January 2018. The variations in δ18OLW at Lake Nanyihu, located in the lower reach of the Yangtze River, are controlled by precipitation oxygen isotope (δ18OP) composition, temperature and evaporation during the non-monsoon season. However, the variations in δ18OLW at the lakes close to the northern limit of the EASM (Gonghai, Mayinghai and Xihaizi) are affected not only by δ18OP, temperature and evaporation, but also by the replenishment of groundwater during the non-monsoon season. In general, during the non-monsoon season, the variation of δ18OLW exhibits a variety of patterns and the controlling factors across the EASM region are complex. During the monsoon season, although the effect of evaporation-induced isotopic enrichment still affects δ18OLW, the variations in δ18OLW are more influenced by the supply of abundant precipitation with lower δ18OP to the lakes, which caused a substantial decrease in δ18OLW across the EASM region in this season. Therefore, the variations in δ18OLW mainly reflect the δ18OP of the EASM during the monsoon season. However, the timing of the peak in monsoon precipitation does not correspond well to minima in δ18OLW, and correlation analysis reveals that there is only a weak relationship between δ18OLW and precipitation/humidity at all four lakes during the monsoon season. These findings demonstrate that although δ18OLW can represent the δ18OP of the EASM, it does not reflect precipitation/humidity during the monsoon season. Overall, our findings indicate that the seasonal variations of δ18OLW across the EASM region are controlled by different climatic variables, which implies that the interpretation of lacustrine δ18O records across the EASM region as an indicator of regional effective precipitation/humidity needs to be reassessed.

中文翻译：

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东亚夏季风区四个湖泊湖水氧同位素组成的季节性变化：对古同位素记录解释的启示

对气候变量与湖水氧同位素 (δ18OLW) 组成之间关系的现代过程研究的缺乏限制了我们对来自湖泊沉积物的氧同位素 (δ18O) 记录的气候意义的理解。我们测量了 2016 年 12 月至 2018 年 1 月东亚夏季风 (EASM) 区域不同位置的四个湖泊（南一湖、公海、马英海和西海子）的 δ18OLW 变化。位于下游的南一湖的 δ18OLW 变化长江流域受降水氧同位素（δ18OP）成分、温度和非季风季节蒸发量控制。然而，靠近东亚夏季风北限的湖泊（贡海、马英海和西海子）的δ18OLW变化不仅受δ18OP、温度和蒸发的影响，也可以通过非季风季节补充地下水。总体而言，非季风季节δ18OLW变化规律多样，整个东亚夏季风地区的控制因素较为复杂。在季风季节，虽然蒸发诱导同位素富集的影响仍然影响δ18OLW，但δ18OLW的变化更多地受到湖泊δ18OP较低的丰富降水供应的影响，导致整个EASM地区δ18OLW大幅下降。这一季。因此，δ18OLW 的变化主要反映了季风季节东亚夏季风的δ18OP。然而，季风降水峰值的时间与 δ18OLW 的最小值并没有很好的对应关系，相关性分析表明，在季风季节，所有四个湖泊的δ18OLW与降水/湿度之间只有微弱的关系。这些发现表明，虽然 δ18OLW 可以代表东亚夏季风的 δ18OP，但它并不能反映季风季节的降水/湿度。总体而言，我们的研究结果表明，整个东亚夏季风地区 δ18OLW 的季节性变化受不同气候变量的控制，这意味着需要重新评估对整个东亚夏季风地区湖泊 δ18O 记录作为区域有效降水/湿度指标的解释。