Cosmogenic surface exposure dating of southern Laurentide ice retreat and eastward Lake Agassiz routing: relationship to the Younger Dryas cold event

南劳伦泰冰退缩和东阿加西湖路线的宇宙成因表面暴露测年：与新仙女木寒冷事件的关系

• 批准号: 1449946
• 负责人: Anders Carlson
• 金额: $ 23.49万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-02-01 至 2018-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1449946&HistoricalAwards=false
• 关键词: Cosmogenic; surface; exposure; dating; southern

Cosmogenic surface exposure dating of southern Laurentide ice retreat and eastward Lake Agassiz routing: relationship to the Younger Dryas cold eventAnders E. Carlson College of Earth, Ocean, and Atmospheric Sciences, Oregon State UniversityThe Younger Dryas (YD) was an abrupt climate change event during the last deglaciation that cooled the North Atlantic region 12,900-11,700 years ago. Ever since its identification over a century ago, the cause of the YD has been widely debated. YD climate cooling was likely caused by a reduction in the strength of the Gulf Stream/North Atlantic current, but what caused this weakening of ocean circulation? This project will test one of the leading hypotheses as to the cause of the YD; that eastward meltwater discharge from the Laurentide Ice Sheet (LIS) freshened the ocean surface and slowed ocean circulation. Given the heightened awareness over tipping points in the climate system, the findings of this project will provide insight into the possible effects of current and future changes in the Arctic freshwater budget. In particular, can only small changes in the Arctic freshwater discharge to the North Atlantic drive significant changes in ocean circulation leading to North Atlantic cooling? Results will also have implications for the field of archeology and geobiology as they will help assess potential underlying causes of Pleistocene large mammal extinction and adaptations of early North Americans, garnering popular attention. How have past abrupt climate change events affected humans? This project will support a postdoctoral researcher, who will be trained in the field of glacial geology, geochronology, geochemistry and paleoclimatology. Under-represented groups in the geosciences will take precedent in recruitment of the postdoctoral researcher. Because of the reduced number of permanent positions in paleoclimatology at present, support of recent PhDs is a significant broader impact. The goal of this project is to determine if the opening of eastern Lake Agassiz outlets occurred at the start of the YD, which would support the hypothesis that this routing caused the YD. The northward retreat of the southern LIS margin and opening of the eastern glacial Lake Agassiz outlets will be directly dated with boulder 10-Be surface exposure ages along the western shores of Lake Superior (the eastern outlet). If one or more of the eastern Lake Agassiz outlets opened at the start of the YD, then eastward runoff routing likely provided the freshwater forcing that drove the reduction in Atlantic meridional overturning strength. A later opening of the eastern outlets would suggest that northwest Lake Agassiz routing or another forcing was the trigger of the YD. Resolving the cause of the canonical abrupt climate event will have important implications on the underlying mechanisms that give rise to nonlinearities in the climate system and will provide a critical target for assessing climate model sensitivity to freshwater forcing. Likewise, the 10-Be chronology can be readily incorporated into glacial systems models that are simulating the last deglaciation of the LIS. Results will be disseminated to the scientific community through publications and presentations at international meetings. Carlson will continue to write popular science pieces, which will incorporate the results of this research project.

南劳伦泰冰退缩和东阿加西湖路线的宇宙成因表面暴露测年：与新仙女木寒冷事件的关系安德斯·卡尔森地球、海洋和大气科学学院，俄勒冈州立大学新仙女木（YD）是一个突然的气候变化事件12,900-11,700 年前最后一次冰消期使北大西洋地区变冷。自从一个多世纪前被确认以来，YD 的成因一直受到广泛争论。 YD气候变冷很可能是由于墨西哥湾流/北大西洋洋流强度减弱造成的，但是什么导致了海洋环流的减弱呢？该项目将测试关于 YD 成因的主要假设之一；劳伦泰德冰原（LIS）向东排放的融水使海洋表面变得清新，并减缓了海洋环流。鉴于人们对气候系统临界点的认识不断提高，该项目的研究结果将深入了解北极淡水预算当前和未来变化的可能影响。特别是，北极淡水向北大西洋排放的微小变化是否会导致海洋环流发生重大变化，从而导致北大西洋变冷？研究结果还将对考古学和地球生物学领域产生影响，因为它们将有助于评估更新世大型哺乳动物灭绝的潜在根本原因以及早期北美的适应，从而引起广泛关注。过去突然的气候变化事件如何影响人类？该项目将支持一名博士后研究员，他们将接受冰川地质学、地质年代学、地球化学和古气候学领域的培训。地球科学领域代表性不足的群体将优先招聘博士后研究员。由于目前古气候学领域的永久职位数量减少，对最近的博士学位的支持会产生更广泛的影响。该项目的目标是确定阿加西湖东部出口的开放是否发生在 YD 开始时，这将支持该路线导致 YD 的假设。 LIS 南部边缘的向北退缩和东部冰川阿加西湖出口的开放将直接用苏必利尔湖西岸（东部出口）的巨石 10-Be 表面暴露年龄来确定年代。如果阿加西湖东部的一个或多个出水口在YD开始时打开，那么向东的径流路径可能会提供淡水强迫，从而导致大西洋经向翻转强度的减少。东部出口的后期开放表明西北阿加西湖路线或其他强迫是 YD 的触发因素。解决典型气候突变事件的原因将对引起气候系统非线性的潜在机制产生重要影响，并将为评估气候模型对淡水强迫的敏感性提供关键目标。同样，10-Be 年代学可以很容易地纳入模拟 LIS 最后一次冰消期的冰川系统模型中。结果将通过出版物和国际会议上的演讲传播给科学界。卡尔森将继续撰写科普文章，其中将纳入该研究项目的成果。