Winter precipitation changes during the Medieval Climate Anomaly and the Little Ice Age in arid Central Asia
Winter precipitation changes during the Medieval Climate Anomaly and the Little Ice Age in arid Central Asia
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DOI：
10.1016/j.quascirev.2017.10.026
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发表时间：
2017-04
影响因子：
4
通讯作者：
J. Fohlmeister;B. Plessen;A. Dudashvili;R. Tjallingii;C. Wolff;A. Gafurov;Hai Cheng
中科院分区：
文献类型：
--
作者：
J. Fohlmeister;B. Plessen;A. Dudashvili;R. Tjallingii;C. Wolff;A. Gafurov;Hai Cheng
北大西洋涛动(NAO)的强度被认为是上个千年欧洲和西亚大陆气候变化的主要驱动因素。例如，欧洲上空以温暖为主的中世纪气候异常(MCA)和随后的小冰期(LIA)冷期与具有正负NAO指数的长期阶段有关。它的气候印记在欧洲冬季尤为明显。然而，关于NAO对欧亚大陆东部范围的影响，人们知之甚少。这里我们介绍了费尔干纳盆地南缘(中亚)的洞穴记录(δ13C，δ18O和Sr/Ca)，揭示了过去1000年来每年可分辨的气候变化。石笋的年龄控制依赖于放射性碳测年，因为大量的碎屑物质阻碍了准确的230Th测年。现今石笋的钙化在春季最有效，因为洞穴大气、融雪和春季降雨量大而提高的供水提供了最佳条件。降水季节变化引起稳定同位素和锶/钙组成的变化。然而，这些地球化学指标的同时变化也为洞穴中的分馏过程提供了证据。通过对这两个过程的分离，我们证明了MCA期间的冬季降水量普遍高于LIA期间，这与与NAO指数相关的气候变化一致，但与中亚地区的高山记录相反。在LIA期间，在中亚观察到了几次冬季降水强烈减少的事件。这些干燥的冬季事件可能与NAO指数强负的阶段有关，所有结果都表明，欧亚大陆中部冬季降水与大气NAO模通过西风系统有密切的联系。
The strength of the North Atlantic Oscillation (NAO) is considered to be the main driver of climate changes over the European and western Asian continents throughout the last millennium. For example, the predominantly warm Medieval Climate Anomaly (MCA) and the following cold period of the Little Ice Age (LIA) over Europe have been associated with long-lasting phases with a positive and negative NAO index. Its climatic imprint is especially pronounced in European winter seasons. However, little is known about the influence of NAO with respect to its eastern extent over the Eurasian continent.Here we present speleothem records (δ13C, δ18O and Sr/Ca) from the southern rim of Fergana Basin (Central Asia) revealing annually resolved past climate variations during the last millennium. The age control of the stalagmite relies on radiocarbon dating as large amounts of detrital material inhibit accurate230Th dating. Present-day calcification of the stalagmite is most effective during spring when the cave atmosphere and elevated water supply by snow melting and high amount of spring precipitation provide optimal conditions. Seasonal precipitation variations cause changes of the stable isotope and Sr/Ca compositions. The simultaneous changes in these geochemical proxies, however, give also evidence for fractionation processes in the cave. By disentangling both processes, we demonstrate that the amount of winter precipitation during the MCA was generally higher than during the LIA, which is in line with climatic changes linked to the NAO index but opposite to the higher mountain records of Central Asia. Several events of strongly reduced winter precipitation are observed during the LIA in Central Asia. These dry winter events can be related to phases of a strong negative NAO index and all results reveal that winter precipitation over the central Eurasian continent is tightly linked to atmospheric NAO modes by the westerly wind systems.