Abstract Modern observations document increased drought frequency together with more intense precipitation and flooding in the world’s semi-arid and arid regions as a consequence of the warming climate. Climate models predict that such conditions will intensify in the future, impacting millions of people. Paleoclimate studies can complement the short modern observational record and model projections by documenting climate changes in the past. Here we report major shifts in the geographic sources, intensity, and seasonality of Eastern Mediterranean precipitation during the unusually warm last interglacial period Marine Isotope Stage (MIS) 5e, reflecting global shifts in the rain and desert belts, based on 234U/238U-ratios in mineral precipitates in the Dead Sea, combined with evidence from climate model simulations. In the Dead Sea catchment 234U/238U ratios are indicators of water sources, where the Jordan River (flowing from the north) and the western catchments show high activity ratios between ∼1.5–1.7, and the eastern and southern catchments and flash floods (in the south-west, south and east) show lower ratios of 1.0–1.2. In Dead Sea water and precipitated minerals, 234U/238U is nearly always ∼1.45–1.55 during both glacials and interglacials. However, during the last interglacial MIS 5e insolation peak (∼127–122 ka) its value decreased to 1.2–1.3, and then to ∼1.0 towards its end (∼122–116 ka). During the insolation peak, the U-isotope data, combined with climate model runs forced with period orbital and greenhouse gas concentrations, indicate that rainfall associated with the African Summer Monsoon in the Dead Sea catchment accounted for ∼50% of the total annual rainfall, in stark contrast to present-day dry summers. The geochemical evidence indicates that following the insolation peak the region experienced an extremely dry period (although punctuated with wetter intervals), signifying expansion of the desert belt, similar to predicted effects of anthropogenic warming. This drying is partly supported by climate model runs forced with the appropriate changes in orbital parameters. The extreme drying during late MIS 5e between ∼122–116 ka reflected a major weakening of Mediterranean storm systems, resulting in a major decline of the Jordan River flow (indicated by the low 234U/238U ratios in the Dead Sea) and a relative increase in precipitation associated with the African Monsoon, shifting towards autumn. The Jordan River flow is estimated to be ∼10% of the present-day (pre-1964, prior to major diversion of the Jordan River and its sources for human use). Such changes, if they occur in the future, have serious implications for future water availability in the politically sensitive Middle East.

中文翻译：

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干旱、洪水事件以及水源和季节性变化是上次间冰期黎凡特气候的特征

摘要 现代观测表明，由于气候变暖，世界半干旱和干旱地区干旱频率增加，降水和洪水更加强烈。气候模型预测，这种情况在未来会加剧，影响数百万人。古气候研究可以通过记录过去的气候变化来补充简短的现代观测记录和模型预测。在这里，我们报告了在异常温暖的末次间冰期海洋同位素阶段 (MIS) 5e 期间东地中海降水的地理来源、强度和季节性的重大变化，反映了雨带和沙漠带的全球变化，基于 234U/238U 比率在死海的矿物沉淀物中，结合气候模型模拟的证据。在死海流域，234U/238U 比率是水源的指标，其中约旦河（从北部流出）和西部流域显示出约 1.5-1.7 之间的高活动率，东部和南部流域和山洪暴发（在西南部、南部和东部）的比率较低，为 1.0-1.2。在死海水和沉淀矿物质中，234U/238U 在冰期和间冰期几乎总是 1.45-1.55。然而，在最后一次间冰期 MIS 5e 日照峰值（~127-122 ka）期间，其值下降到 1.2-1.3，然后在接近结束时降至~1.0（~122-116 ka）。在日照高峰期间，U 同位素数据结合气候模型运行，受周期轨道和温室气体浓度的影响，表明与死海集水区的非洲夏季风相关的降雨量约占年总降雨量的 50%，与当今干燥的夏季形成鲜明对比。地球化学证据表明，在日照高峰之后，该地区经历了一个极其干旱的时期（尽管中间有更潮湿的间隔），这意味着沙漠带的扩张，类似于人为变暖的预测影响。这种干燥在一定程度上得到了气候模型运行的支持，这些模型运行是在轨道参数的适当变化下进行的。MIS 5e 后期的极端干燥在 ∼122-116 ka 之间反映了地中海风暴系统的严重减弱，导致约旦河流量大幅下降（死海 234U/238U 比率较低）和与非洲季风相关的降水相对增加，向秋季转移。约旦河的流量估计约为今天的 10%（1964 年之前，在约旦河及其源头供人类使用之前）。如果将来发生此类变化，将对政治敏感的中东地区未来的水资源供应产生严重影响。