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

在最后一次消冰期间，整个北半球的全球水文重组与北大西洋北部地区重复的次千年尺度的大气候变化是同步发生的。然而，这种重组如何影响干旱易发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矛盾的，这主要是由于两个差异来源：(1)年龄约束的不确定性；(2)基于洞穴的代理记录的基本模糊性。该项目由加州大学戴维斯分校和哈佛大学的科学家合作完成，旨在利用加州内华达山脉的洞穴沉积物，解决美国西南部推断的冰期-间冰期气候重建中明显的矛盾。研究人员将采用新技术，在研究地点产生一个强大的年代学框架（通过激光烧蚀MC-ICPMS使用U-Th定年法）和降水记录（使用流体包裹体中依赖温度的稀有气体浓度作为独立于其他气候过程的温度代用物，包裹体流体的稳定同位素组成作为降水组成和来源区域的更直接代用物）。这些创新方法的成功概念验证将为古气候中各种各样的问题的应用打开大门。这项工作的结果应该有助于更好地了解气候变化如何影响美国西南部的水文气候，这是一个容易受到水资源限制的地区。其他更广泛的影响包括开发常规高精度u系列测年的新设备（在美国只有少数），开发碳酸盐岩中的稀有气体代理，以及在两所机构培训研究生。

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.