Collaborative Research: Quantifying past water table depth and hydroclimate with dissolved noble gas isotopes in groundwater

水资源是美国干旱地区农业的一个关键问题，水的可用性可能会受到未来气候变化的影响，但仍然很难预测未来降雨量变化的幅度。拟议的研究将开发一种新的精确方法，利用古代地下水中溶解的惰性气体同位素的测量来量化过去地下水位深度的变化。 过去地下水位波动的知识将有助于阐明区域降雨对气候变化的反应，并通过提供严格的降雨模型测试来加强预测。该方法是基于这样一个已证实的事实，即重气体沉降到地下水位深度以上的土壤中的静止空气柱的底部。 地下水位越深，重同位素的富集程度越高，这些重同位素溶解在水中，从而保存了关于含有古代地下水的含水层的地下水位深度的信息。 已经对这种地下水进行了例行取样，以了解过去惰性气体丰度的温度;拟议的研究将增加地下水位深度，以增加可以从样本中提取的信息。

Water resources are a critical issue for agriculture in the arid parts of the US, and it is likely that water availability will be affected by future climate change, yet it remains difficult to predict the magnitude of future rainfall changes. The proposed research will develop a new and precise method for quantifying past changes in water table depth, using measurements of dissolved noble gas isotopes in ancient groundwater. This knowledge of past water table fluctuations will help illuminate the regional rainfall response to climate variations, and strengthen predictions by providing rigorous tests of rainfall models. The method is based on the demonstrated fact that heavy gases settle to the bottom of the stagnant column of air in the soil above the water table depth. The deeper the water table, the more extreme the enrichment of heavy isotopes, and these heavy isotopes become dissolved in the water thus preserving information about the water table depth in aquifers containing ancient groundwater. This groundwater is already routinely sampled to learn about past temperature from the abundance of the noble gases; the proposed research will add water table depth to the information that can be extracted from the samples.