In eastern Africa, there are few long, high-quality records of environmental change at high altitudes, inhibiting a broader understanding of regional climate change. We investigated a Holocene lacustrine sediment archive from Lake Garba Guracha, Bale Mountains, Ethiopia, (3,950 m asl), and reconstructed high-altitude lake evaporation history using δ18O records derived from the analysis of compound-specific sugar biomarkers and diatoms. The δ18Odiatom and δ18Ofuc records are clearly correlated and reveal similar ranges (7.9‰ and 7.1‰, respectively). The lowest δ18O values occurred between 10–7 cal ka BP and were followed by a continuous shift towards more positive δ18O values. Due to the aquatic origin of the sugar biomarker and similar trends of δ18Odiatom, we suggest that our lacustrine δ18Ofuc record reflects δ18Olake water. Therefore, without completely excluding the influence of the ‘amount-effect’ and the ‘source-effect’, we interpret our record to reflect primarily the precipitation-to-evaporation ratio (P/E). We conclude that precipitation increased at the beginning of the Holocene, leading to an overflowing lake between ca. 10 and ca. 8 cal ka BP, indicated by low δ18Olake water values, which are interpreted as reduced evaporative enrichment. This is followed by a continuous trend towards drier conditions, indicating at least a seasonally closed lake system.

中文翻译：

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基于糖生物标志物和硅藻 δ18O 记录的埃塞俄比亚贝尔山脉非洲高山加尔巴古拉查湖全新世湖泊蒸发历史

在东非，关于高海拔环境变化的长期高质量记录很少，阻碍了对区域气候变化的更广泛了解。我们调查了埃塞俄比亚贝尔山脉加尔巴古拉查湖 (3,950 m asl) 的全新世湖泊沉积物档案，并使用 δ 重建高海拔湖泊蒸发历史18O 记录来自化合物特异性糖生物标志物和硅藻的分析。δ18○硅藻和δ18○操记录明显相关并显示相似的范围（分别为 7.9‰ 和 7.1‰）。最低的 δ18O 值发生在 10-7 cal ka BP 之间，随后连续向更正的 δ 转变18O 值。由于糖生物标志物的水生来源和 δ 的类似趋势18○硅藻, 我们建议我们的湖泊 δ18○操记录反映 δ18○湖水. 因此，在不完全排除“量效应”和“源效应”的影响的情况下，我们将我们的记录解释为主要反映降水-蒸发比（P/E）。我们得出结论，在全新世初期降水增加，导致大约在 2000 年前后出现溢出的湖泊。10 岁左右 8 cal ka BP，由低 δ 表示18○湖水值，这被解释为减少的蒸发富集。随后是干旱条件的持续趋势，表明至少有一个季节性封闭的湖泊系统。