ABSTRACT East Africa is an underrepresented region in respect of monitoring the stable isotopic composition of precipitation (δ18Oprec and δ2Hprec). In 2017, we collected precipitation samples from ten weather stations located along an altitudinal transect ranging from 1304 to 4375 m a.s.l. The δ18Oprec and δ2Hprec values varied from –8.7 to +3.7 ‰ and –38 to +29 ‰, respectively. The local meteoric water line is characterised by a lower slope, a higher intercept and more positive d-excess values (δ2H = 5.3 ± 0.2 * δ18O + 14.9 ± 0.9) compared to the global meteoric water line. Both altitude and amount of precipitation clearly correlate with our isotope data. However, the δ18Oprec and δ2Hprec values show at the same time a seasonal pattern reflecting rainy versus dry season. More enriched isotope values prevailed shortly after the end of the dry season; more depleted isotope values coincided with high precipitation amounts recorded in May, August and September. Moreover, HYSPLIT trajectories reveal that during the dry season water vapour originates primarily from the Arabian Sea, whereas during the wet season it originates primarily from the Southern Indian Ocean. These findings challenge the traditional amount effect interpretation of paleoclimate isotope records from East Africa and rather point to a previously underestimated source effect.

中文翻译：

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埃塞俄比亚贝尔山脉当代降水的 2H 和 18O 同位素时空变化

摘要 在监测降水的稳定同位素组成（δ18Oprec 和 δ2Hprec）方面，东非是一个代表性不足的地区。2017 年，我们从位于 1304 至 4375 m asl 海拔断面的 10 个气象站采集了降水样本，δ18Oprec 和 δ2Hprec 值分别从 –8.7 至 +3.7 ‰ 和 –38 至 +29 ‰ 变化。与全球大气水线相比，当地大气水线的特点是斜率更低、截距更高、d-excess 值更正（δ2H = 5.3 ± 0.2 * δ18O + 14.9 ± 0.9）。海拔高度和降水量都与我们的同位素数据明显相关。然而，δ18Oprec 和 δ2Hprec 值同时显示出反映雨季与旱季的季节性模式。在旱季结束后不久，更富集的同位素值占了上风；更多的贫化同位素值恰逢 5 月、8 月和 9 月记录的高降水量。此外，HYSPLIT 轨迹显示，在旱季，水汽主要来自阿拉伯海，而在雨季，它主要来自南印度洋。这些发现挑战了对东非古气候同位素记录的传统数量效应解释，而是指出了先前被低估的源效应。而在雨季，它主要来自南印度洋。这些发现挑战了对东非古气候同位素记录的传统数量效应解释，而是指出了先前被低估的源效应。而在雨季，它主要来自南印度洋。这些发现挑战了对东非古气候同位素记录的传统数量效应解释，而是指出了先前被低估的源效应。