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

南劳伦蒂德冰退缩和阿加西兹湖东进的宇宙成因表面暴露定年：与新仙女木冷事件的关系。卡尔森地球、海洋和大气科学学院，俄勒冈州州立大学新仙女木（YD）是12900 - 11700年前最后一次冰消期的一次突然气候变化事件，使北大西洋地区冷却。自世纪前被发现以来，关于“青年节”的原因一直存在着广泛的争论。YD气候变冷可能是由墨西哥湾流/北大西洋洋流强度的减弱引起的，但是是什么导致了海洋环流的减弱呢？该项目将测试关于YD原因的主要假设之一;从Laurentide冰盖（LIS）向东排放的融水使海洋表面清新，减缓了海洋环流。鉴于人们对气候系统临界点的认识有所提高，该项目的研究结果将有助于深入了解北极淡水收支目前和未来变化的可能影响。特别是，北极淡水排放到北大西洋的微小变化是否会导致海洋环流的重大变化，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和早期北美人适应的潜在根本原因，从而引起广泛关注。过去的气候突变事件如何影响人类？该项目将资助一名博士后研究员，他将在冰川地质学、地质年代学、地球化学和古气候学领域接受培训。在招聘博士后研究人员时，地球科学领域代表性不足的群体将优先考虑。由于目前古气候学永久职位的数量减少，最近的博士学位的支持是一个显着的更广泛的影响。本项目的目标是确定东部阿加西湖出口的开放是否发生在YD开始时，这将支持这一路由导致YD的假设。向北撤退的南部LIS边缘和开放的东部冰川湖阿加西出口将直接与巨石10-被表面暴露年龄沿着西海岸的湖上级（东部出口）。如果阿加西湖东部的一个或多个出口在YD开始时开放，那么向东的径流路由可能提供了淡水强迫，导致大西洋纬向倾覆强度降低。后来东部出口的开放将表明西北阿加西湖路由或另一种强迫是YD的触发。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，并将为评估气候模式对淡水强迫的敏感性提供关键目标。同样，10-Be年表可以很容易地纳入冰川系统模型，模拟最后一次冰消期的LIS。研究结果将通过出版物和在国际会议上的发言向科学界传播。卡尔森将继续撰写科普文章，其中将纳入这一研究项目的结果。

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.