Influence of tropical easterlies in southern Africa's winter rainfall zone during the Holocene
Influence of tropical easterlies in southern Africa's winter rainfall zone during the Holocene
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DOI：
10.1016/j.quascirev.2014.10.011
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发表时间：
2015-01-01
影响因子：
4
通讯作者：
Reimer, Paula J.
中科院分区：
文献类型：
--
作者：
Chase, Brian M.;Lim, Sophak;Reimer, Paula J.
南非西南部的开普省位于南半球温带(冬季)和热带(夏季)湿度系统之间的关键过渡地带。在最近的地质历史中，有人提出，这些系统的相对影响可能已经发生了实质性的变化，但关于区域水文气候和降雨季节性的可靠证据很少，无法完善或充实对长期动态的理解。在这篇文章中，我们提出了一个全新世中晚期的环境变化的多代理记录，来自Katbakies Pass的一个岩石Hyrax Midden，位于冬季和夏季降雨带之间的现代边界上。这些数据来自稳定的碳和氮同位素、化石花粉和微木炭，提供了湿度变化的高分辨率记录，并洞察了降雨季节性的变化。以前的研究得出结论认为，该遗址在全新世期间通常只经历了微小的环境变化，但我们的记录表明，在过去的7000年里，该地区发生了重大的、突然的变化。与基于场地位置的预期相反，这些数据表明，湿度变化的主要决定因素是夏季而不是冬季降雨量的变化，及其对干旱季节强度和/或时间的影响。这些发现与南部和西部海岸上升流的独立记录一致，表明湿度增加的时期与热带东风气流增加有关。这大大加深了我们对非洲西南部温带和热带环流系统动力学性质的理解，以及它们相对优势地位的变化如何影响了全新世的区域环境。(C)2014爱思唯尔有限公司。保留所有权利。
South Africa's southwestern Cape occupies a critical transition zone between Southern Hemisphere temperate (winter) and tropical (summer) moisture-bearing systems. In the recent geological past, it has been proposed that the relative influence of these systems may have changed substantially, but little reliable evidence regarding regional hydroclimates and rainfall seasonality exists to refine or substantiate the understanding of long-term dynamics. In this paper we present a mid-to late Holocene multi-proxy record of environmental change from a rock hyrax midden from Katbakkies Pass, located along the modern boundary between the winter and summer rainfall zones. Derived from stable carbon and nitrogen isotopes, fossil pollen and microcharcoal, these data provide a high resolution record of changes in humidity, and insight into changes in rainfall seasonality. Whereas previous work concluded that the site had generally experienced only subtle environmental change during the Holocene, our records indicate that significant, abrupt changes have occurred in the region over the last 7000 years. Contrary to expectations based on the site's location, these data indicate that the primary determinant of changes in humidity is summer rather than winter rainfall variability, and its influence on drought season intensity and/or length. These findings are consistent with independent records of upwelling along the southern and western coasts, which indicate that periods of increased humidity are related to increased tropical easterly flow. This substantially refines our understanding of the nature of temperate and tropical circulation system dynamics in SW Africa, and how changes in their relative dominance have impacted regional environments during the Holocene. (C) 2014 Elsevier Ltd. All rights reserved.