A 350,000 - Year History of Rainfall and Temperature in Tropical East Africa

热带东非 35 万年的降雨量和气温历史

• 批准号: 0902714
• 负责人: Tom Johnson
• 金额: $ 45.46万
• 依托单位: University of Minnesota Duluth
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0902714&HistoricalAwards=false
• 关键词: 350; 000; Year; History; Rainfall

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This award supports analyses of two cores recovered in 2005 from the floor of Lake Malawi, in Africa. These cores contain approximately 350,000 years of temperature and rainfall proxies from the central basin of Lake Malawi. Initial results from the Lake Malawi Drilling Project have thus far provided: (1) surprising new insights into the recurrence and intensity of drought in East Africa for the past 150,000 years, (2) a preliminary estimate of past lake ecosystem dynamics, (3) compelling evidence for a tie between the climate in this part of the African tropics with the bipolar see-saw, and (4) a thermal history of the region that extends back 75,000 years. This project addresses the following questions: 1. To what extent do temperature and rainfall follow insolation forcing of either hemisphere? 2. What is the relationship between temperature and humidity shifts in the Malawi basin and concentrations of atmospheric CO2 and CH4? 3. What is the nature of millennial-scale variation in temperature and rainfall in the Malawi basin over the past ~500,000 years? 4. To what extent do temperature and rainfall in the Malawi basin respond to the sea-surface temperature regime of the tropical Pacific and Indian Oceans? The project obtains estimates of past rainfall from analyses of the del-D record derived from long-chain fatty acids and of the del-13C record preserved in the long-chain n-alkanes of terrestrial vegetation preserved in Lake Malawi sediment. Estimates of past temperature are based on a paleotemperature proxy for the marine environment called TEX86. This approach has provided promising results from previous work on both Lake Malawi and Lake Tanganyika in East Africa. The group continues to improve on the age model of the long Malawi drill core, focusing on U/Th dating of carbonate nodules that are found at a few, carbonate-rich intervals in the core. These dates are supplemented with precessional tuning of the carbonate abundance record.The climate history of tropical Africa portends a future of recurring severe and long-lasting drought that will have enormous impact on human welfare in the region. The data that will be provided from this research will be invaluable for comparison to marine sediment and speleothem records from the tropics that span the past few hundred thousand years, and for testing the accuracy of climate models that are necessary to improve long-term weather forecasts for this heavily populated portion of the African continent. The project involves graduate and undergraduate students in laboratory analyses and in all aspects of interpretation and dissemination of results, through graduate thesis research and undergraduate research opportunities.

该奖项是根据2009年《美国复苏和再投资法》(公法111-5)资助的。该奖项支持对2005年在非洲马拉维湖湖底发现的两个岩芯的分析。这些岩心包含来自马拉维湖中央盆地的大约350,000年的温度和降雨量。马拉维湖钻探项目迄今取得的初步成果有：(1)对过去150,000年来东非干旱的反复和严重程度有了令人惊讶的新见解；(2)对过去湖泊生态系统动态的初步估计；(3)令人信服的证据表明，非洲热带这一地区的气候与两极拉锯法有关；(4)该区域的热史可以追溯到75,000年前。这个项目解决了以下问题：1.温度和降水在多大程度上伴随着两个半球的日照强迫？2.马拉维盆地的温度和湿度变化与大气CO2和CH4浓度之间的关系是什么？3.马拉维盆地过去500,000年来温度和降水的千年尺度变化的性质是什么？4.马拉维盆地的温度和降水在多大程度上响应热带太平洋和印度洋的海面温度变化？该项目通过分析来自长链脂肪酸的del-D记录和马拉维湖沉积物中保存的陆地植被长链正构烷烃中保存的del-13C记录，得到过去降雨量的估计值。对过去温度的估计是基于一个名为TEX86的海洋环境的古温度替代指标。这一方法在东非马拉维湖和坦噶尼喀湖以前的工作中取得了令人振奋的成果。该小组继续改进马拉维长钻探岩心的年龄模型，重点是对在岩心中几个富含碳酸盐的区间发现的碳酸盐结核进行U/Th测年。这些日期加上碳酸盐丰度记录的进动调谐。热带非洲的气候历史预示着未来将反复出现严重和长期干旱，这将对该区域的人类福祉产生巨大影响。这项研究将提供的数据对于与热带过去数十万年来的海洋沉积物和洞穴沉积记录进行比较，以及测试气候模型的准确性将是非常宝贵的，气候模型对于改善非洲大陆这一人口稠密地区的长期天气预报是必要的。该项目让研究生和本科生参与实验室分析，并通过研究生论文研究和本科生研究机会，在所有方面解释和传播结果。