Ice-sheet modulation of deglacial North American monsoon intensification
Ice-sheet modulation of deglacial North American monsoon intensification
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DOI：
10.1038/s41561-018-0220-7
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发表时间：
2018-11-01
影响因子：
18.3
通讯作者：
Murray, James W.
中科院分区：
文献类型：
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作者：
Bhattacharya, Tripti;Tierney, Jessica E.;Murray, James W.
北美季风是美国西南部干旱地区的主要降雨源，但它仍然是人们最不了解的季风系统之一。这种季风的晚更新世演化受到的限制很少，主要是因为冬季降雨的冰川变化掩盖了许多区域代理记录中的夏季季风特征。在这里，我们通过海洋沉积物岩心中叶蜡生物标志物的同位素分析来开发季风强度的冰消记录。重建表明末次盛冰期期间季风降雨量出现区域性减少，并且北美季风的冰消轨迹密切跟踪北美冰盖的变化。在气候模型模拟中，北美冰盖使西风带向南移动，有利于寒冷干燥的空气进入美国西南部。这一过程称为通风，通过稀释对流所需的能量通量来削弱季风。随着冰盖向北退缩，季风加强，当地海洋条件可能在调节其强度方面发挥更大的作用。我们的结论是，在冰期-间冰期时间尺度上，冰盖引起的大气环流重组对北美季风具有主导影响。
The North American monsoon, the dominant source of rainfall for much of the arid US Southwest, remains one of the least understood monsoon systems. The late Pleistocene evolution of this monsoon is poorly constrained, largely because glacial changes in winter rainfall obscure summer monsoon signatures in many regional proxy records. Here, we develop deglacial records of monsoon strength from isotopic analyses of leaf wax biomarkers in marine sediment cores. Reconstructions indicate a regional decrease in monsoon rainfall during the Last Glacial Maximum, and that the deglacial trajectory of the North American monsoon closely tracks changes in North American ice cover. In climate model simulations, North American ice cover shifts the westerlies southwards, favouring the mixing of cold, dry air into the US Southwest. This process, known as ventilation, weakens the monsoon by diluting the energy fluxes required for convection. As the ice sheet retreats northwards, the monsoon strengthens, and local ocean conditions may play a larger role in regulating its intensity. We conclude that on glacial-interglacial timescales, ice-sheet-induced reorganizations of atmospheric circulation have a dominant influence on the North American monsoon.