Collaborative Research: Calibrating the Isotopologue-47 Geothermometer in Soils

在过去的几年里，使用同位素-47古温度计是一个令人兴奋的新发展，在更深的地质记录中重建古温度具有巨大的潜力。古土壤碳酸盐是此类分析的一个特别有吸引力的目标，因为它们在地质记录中非常丰富，而且土壤中的温度与气温显示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，必须严格建立从现代土壤碳酸盐的同位素-47分析中估计的温度与当地气温和土壤温度之间的关系。我们给出了一些现代土壤的未发表的结果，这些结果表明，从±47值估计的温度系统地比模拟的夏季最高温度高6±2°C。部分超出？高达2-4°C？可以解释土壤夏季加热的不对称。剩余的过剩可能是污染、错误假设的土壤温度，或者可能是非平衡动力学效应的结果。无论是什么原因，更关键的问题是，实际价值和估计价值之间的抵消是否具有系统性。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，涵盖了土壤碳酸盐形成的大部分自然温度范围。鉴于人们对在各种研究问题上使用这种新的地温计有着浓厚的兴趣，这将对更大的科学界产生更广泛的影响。新的古温度计令人兴奋的潜在应用包括利用巴基斯坦西瓦利克等长的古土壤时间序列(17Myr)恢复古温度(±2℃)，以及利用世界主要造山带-S主要造山带温度对海拔的强烈敏感性来恢复古海拔。实地和实验室测量和数据分析是理科本科生的理想培训机会，他们将从几个机构招募参加实地和实验室工作。

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 We present unpublished results from a number of modern soils that show that temperature estimates from Ä47 values systematically exceed those of modeled summer maximum temperatures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.