Collaborative Research: EAGER--Evaluating Fluid Inclusion Geochemistry of U-Th Dated Speleothems as a Tool for Resolving Paleoclimate Controversies in the American Southwest

整个北半球的全球水文重组与北大西洋北部地区在上一次冰川消融期间反复发生的大规模、亚千年规模的气候变化同步进行。然而，这种重组如何影响易发生干旱的美国西南部的大陆水文气候仍然没有得到很好的解决。基于大陆的古气候重建在很大程度上是由于两个不一致的来源：(1)年龄限制的不确定性，(2)基于洞穴喷发的替代记录的根本模糊。该项目--加州大学戴维斯分校和哈佛大学的科学家合作--试图利用加利福尼亚州内华达山脉的洞穴沉积来解决美国西南部推断的冰川-间冰期气候重建中的明显矛盾。研究人员将使用新的技术，在研究地点生成一个稳健的年代学框架(使用激光消融MC-ICPMS的U-Th测年)和过去20,000年来的降水记录(使用流体包裹体中依赖温度的惰性气体浓度作为独立于其他气候过程的温度代理，以及包裹体流体的稳定同位素组成作为降水组成和源区的更直接代理)。这些创新方法的成功概念验证将为应用于古气候中的各种问题打开大门。这项工作的结果应该有助于更好地理解气候变化如何影响美国西南部的水文气候，该地区容易受到水资源限制的影响。其他更广泛的影响包括开发一个用于常规高精度U系列测年的新设施(美国只有少数几个)，开发碳酸盐中的惰性气体代理，以及在两个机构培训研究生。

Global hydrologic reorganization throughout the Northern Hemisphere occurred synchronously with repeated large, sub-millennial-scale climate changes in the northern North Atlantic region during the last deglaciation. However, how this reorganization affected the continental hydroclimate in the drought-prone American Southwest remains poorly resolved. Continental-based paleoclimate reconstructions for this region are contradictory in large part due to two sources of discrepancy: (1) uncertainty in age constraints, and (2) fundamental ambiguity in speleothem-based proxy records.This project-- a collaborative effort between scientists from the University of California at Davis and Harvard University-- seeks to resolve the apparent contradictions in the inferred glacial-interglacial climate reconstructions for the American Southwest using cave deposits from the Sierra Nevada in California. The researchers will employ novel techniques to generate both a robust chronologic framework (using U-Th dating via laser ablation MC-ICPMS) and a record of precipitation (using temperature-dependent noble gas concentrations in fluid inclusions as a temperature proxy independent of other climate processes and stable isotopic composition of inclusion fluids as a more direct proxy of precipitation composition and source region) over the past ~20,000 years at the study site. Successful proof-of-concept of these innovative approaches would open the door for applications to a wide variety of questions in paleoclimate.The outcomes of this work should lead to better understanding of how climate change impacts the hydroclimate of the American Southwest, an area that is vulnerable to water resource limitation. Additional broader impacts include development of a new facility for routine high-precision U-series dating (of which there are only a handful in the US), development of the noble gas proxy in carbonates, and training of graduate students at two institutions.