Expansion and Intensification of the North American Monsoon During the Pliocene
Expansion and Intensification of the North American Monsoon During the Pliocene
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DOI：
10.1029/2022av000757
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发表时间：
2022-11
期刊：
影响因子：
8.4
通讯作者：
Tripti Bhattacharya;R. Feng;J. Tierney;Claire B. Rubbelke;N. Burls;Scott Knapp;M. Fu
中科院分区：
文献类型：
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作者：
Tripti Bhattacharya;R. Feng;J. Tierney;Claire B. Rubbelke;N. Burls;Scott Knapp;M. Fu
与许多亚热带地区一样，预计北美西南部将因人为变暖而变得更加干燥。然而，在上新世，当二氧化碳高于工业化前水平时，多条证据表明SWNA要湿润得多。虽然对潮湿上新世的现有解释援引了冬季降雨的增加，但最近的建模研究假设夏季降雨可能也起了重要作用。在这里，我们利用叶蜡氢同位素提供了SWNA中上新世季风增强的第一个直接证据。这些新记录提供了上新世中期北美季风增强和扩大的证据。利用代用物和同位素模式模拟，我们表明，相对于热带太平洋，季风增强与南加州边缘的升温放大有关。这一机制对于理解当今季风的变化具有明确的相关性，因为我们表明，加利福尼亚边缘的亚热带变暖放大的间隔，如在现代加利福尼亚边缘热浪中所看到的，与更强的季风有关。由于预计海洋热浪的频率将增加，未来可能会出现“类似上新世”的降雨间隔，与西南海区日益加剧的特大干旱共存，对生态系统、人类基础设施和水资源产生影响。
Southwestern North America (SWNA), like many subtropical regions, is predicted to become drier in response to anthropogenic warming. However, during the Pliocene, when carbon dioxide was above pre‐industrial levels, multiple lines of evidence suggest that SWNA was much wetter. While existing explanations for a wet Pliocene invoke increases in winter rain, recent modeling studies hypothesize that summer rain may have also played an important role. Here, we present the first direct evidence for an intensified mid‐Pliocene monsoon in SWNA using leaf wax hydrogen isotopes. These new records provide evidence that the mid‐Pliocene featured an intensified and expanded North American Monsoon. Using proxies and isotope‐enabled model simulations, we show that monsoon intensification is linked to amplified warming on the southern California margin relative to the tropical Pacific. This mechanism has clear relevance for understanding present‐day monsoon variations, since we show that intervals of amplified subtropical warming on the California margin, as are seen during modern California margin heat waves, are associated with a stronger monsoon. Because marine heat waves are predicted to increase in frequency, the future may bring intervals of “Pliocene‐like” rainfall that co‐exist with intensifying megadrought in SWNA, with implications for ecosystems, human infrastructure, and water resources.