Collaborative Research: Calibrating the Isotopologue-47 Geothermometer in Soils

过去几年中 isotopologue-47 古温度计的使用是一项令人兴奋的新发展，它为重建更深层次的地质记录中的古温度提供了巨大的潜力。古土壤碳酸盐是此类分析特别有吸引力的目标，因为它们在地质记录中非常丰富，而且土壤温度与气温之间存在高度可预测的关系（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 isotopologue-47 分析（表示为 ä47）估计的温度与当地空气和土壤温度之间的关系。我们展示了来自许多现代土壤的未发表的结果，这些结果表明，根据 47 值估算的温度系统地超出了模拟的夏季最高温度 6±2°C。部分过量（高达 2-4°C）可能是由于夏季土壤加热不对称造成的。剩余的过量可能是污染、错误假设的土壤温度或非平衡动力学效应的结果。无论原因是什么，更关键的问题是实际值与估计值之间的偏移是否是系统性的。必须使用更大的样本集并直接测量土壤温度来对此进行测试。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 的温度估计值进行比较。我们的研究地点包括亚利桑那州、内华达州、夏威夷州和阿根廷西北部，考虑了土壤碳酸盐形成的大部分自然温度范围。鉴于人们对使用这种新型地温计解决各种研究问题的浓厚兴趣，这对更大的科学界将产生重大影响。新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古土壤时间序列（17 Myr）重建古气温（±2°C），以及通过世界主要造山带温度对海拔的强烈敏感性重建古海拔。现场和实验室测量以及数据分析是科学本科生的理想培训机会，他们将从多个机构招募来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 We present unpublished results from a number of modern soils that show that temperature estimates from Ä47 values systematically exceed those of modeled summer maximum temperatures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.