Stable isotopic evidence of El Niño-like atmospheric circulation in the Pliocene western United States
Stable isotopic evidence of El Niño-like atmospheric circulation in the Pliocene western United States
复制标题
美国西部上新世类厄尔尼诺大气环流的稳定同位素证据
DOI：
10.5194/cp-9-903-2013
复制
发表时间：
2012
影响因子：
4.3
通讯作者：
C. Chamberlain
中科院分区：
文献类型：
--
作者：
M. Winnick;J. Welker;C. Chamberlain
摘要。在人类活动导致大气中二氧化碳浓度持续增加的今天，了解过去的水文循环是如何对全球变暖做出反应的尤为重要。上新世提供了一个理想的窗口，让我们了解与当前大气二氧化碳分压平衡的气候系统。在上新世期间，美国西部比现代湿润，这一观测结果与我们目前对未来变暖情景的理解不一致，未来变暖情景涉及亚热带干旱地区的扩张和向极地迁移。在此，我们比较了美国西部上新世成土碳酸盐的氧同位素剖面与厄尔尼诺-南方涛动（ENSO）期间降水的现代同位素异常。考虑到碳酸盐形成的季节性，我们发现上新世晚期的同位素变化与厄尔尼诺年的现代降水同位素异常相匹配。此外，上新世晚期的同位素变化反映了更新世早期的变化，这可能代表了劳伦泰德冰盖生长引起的西风风暴路径向南迁移。我们提出，西风风暴路径在上新世晚期随着赤道东太平洋现代冷舌的发展向北迁移，然后在北半球广泛的冰川作用下向南返回，这一情景得到了美国陆地气候代理的支持。这些数据共同支持了上新世温暖时期北美西部存在类似厄尔尼诺的背景条件。如果地球对未来变暖的表现类似，这一观测结果对北美西部降水的数量和分布具有重要意义。
Abstract. Understanding how the hydrologic cycle has responded to warmer global temperatures in the past is especially important today as concentrations of CO2 in the atmosphere continue to increase due to human activities. The Pliocene offers an ideal window into a climate system that has equilibrated with current atmospheric pCO2. During the Pliocene the western United States was wetter than modern, an observation at odds with our current understanding of future warming scenarios, which involve the expansion and poleward migration of the subtropical dry zone. Here we compare Pliocene oxygen isotope profiles of pedogenic carbonates across the western US to modern isotopic anomalies in precipitation between phases of the El Nino–Southern Oscillation (ENSO). We find that when accounting for seasonality of carbonate formation, isotopic changes through the late Pliocene match modern precipitation isotopic anomalies in El Nino years. Furthermore, isotopic shifts through the late Pliocene mirror changes through the early Pleistocene, which likely represents the southward migration of the westerly storm track caused by growth of the Laurentide ice sheet. We propose that the westerly storm track migrated northward through the late Pliocene with the development of the modern cold tongue in the east equatorial Pacific, then returned southward with widespread glaciation in the Northern Hemisphere – a scenario supported by terrestrial climate proxies across the US. Together these data support the proposed existence of background El Nino-like conditions in western North America during the warm Pliocene. If the earth behaves similarly with future warming, this observation has important implications with regard to the amount and distribution of precipitation in western North America.