Collaborative Research: Calibrating the Isotopologue-47 Geothermometer in Soils

在过去的几年里，同位素-47古温度表的使用是一项令人兴奋的新发展，它在重建更深层地质记录的古温度方面具有巨大的潜力。古土壤碳酸盐是这种分析的一个特别有吸引力的目标，因为它们在地质记录中是如此丰富，而且因为土壤中的温度与气温表现出高度可预测的关系（与许多其他系统不同）。在实现这一潜力之前，必须严格建立现代土壤碳酸盐同位素-47分析估计的温度（表示为Ä47）与当地空气和土壤温度之间的关系。我们提出了来自许多现代土壤的未发表的结果，表明Ä47值的温度估计系统地超过了模拟的夏季最高温度6±2°C。超额部分？2-4°C？可能是夏季土壤加热不对称的原因。剩余的过量可能是污染的结果，错误假设的土壤温度，或者可能是非平衡动力学效应。不管原因是什么，更关键的问题是，实际值和估计值之间的抵消是否是系统性的。这必须用更大的样本集和土壤温度的直接测量来测试。在这里，我们建议从一系列设置中监测现代土壤中的温度和其他参数，以便与Ä47估计的温度进行比较。我们的研究地点包括亚利桑那州、内华达州、夏威夷和阿根廷西北部，在大多数自然温度范围内进行土壤碳酸盐形成。考虑到在各种研究问题上使用这种新的地温计的强烈兴趣，这对更大的科学界的广泛影响将是实质性的。新的古温度表的潜在应用令人兴奋，包括利用巴基斯坦Siwaliks这样长的古土壤时间序列（17 Myr）重建古温度（±2°C），以及通过世界上温度对海拔高度的强烈敏感性重建古海拔。5个主要造山带。现场和实验室测量和数据分析是理想的训练机会，本科生将从几个机构招募参加现场和实验室工作。

Use of isotopologue-47 paleothermometer over the past several years is an exciting new development that holds enormous potential for reconstruction of paleotemperatures in the deeper geologic record. Paleosol carbonates are a particularly attractive target for such analysis because they are so abundant in the geologic record, and because temperature in soils displays a highly predictable relationship to air temperature (unlike in many other systems). Before this potential can be realized, the relationship between temperatures estimated from isotopologue-47 analysis (expressed as Ä47) of modern soil carbonate, and that of local air and soil temperature must be rigorously established. We present unpublished results from a number of modern soils that show that temperature estimates from Ä47 values systematically exceed those of modeled summer maximum temperatures by 6±2°C. Part of the excess?up to 2-4°C?may be explained asymmetric summer heating of soil. The remaining excess may be the result of contamination, the wrong assumed soil temperatures, or perhaps non-equilibrium kinetic effects. Whatever the cause, the more key question is whether the offset between actual and estimated values is systematic. This must be tested with a much larger sample set and with direct measurements of soil temperature. Here we propose to monitor temperature and other parameters in modern soils from a range of settings for comparison to Ä47 estimates of temperatures. Our study sites include Arizona, Nevada, Hawaii, and NW Argentina, taking in most of the natural temperature range for soil carbonate formation. Broader impacts of this on the larger scientific community will be substantial, given the intense interest in using this new geothermometer on a variety of research questions. Exciting potential applications of the new paleothermometer include reconstruction of paleotemperature (±2°C) using such long paleosol time series (17 Myr) as the Siwaliks in Pakistan, and of paleoelevation, through the strong sensitivity of the temperature to elevation in the world?s major orogens. Field and laboratory measurements and data analysis are ideal training opportunities for undergraduates in the sciences, who will be recruited from several institutions to participate in field and labwork.