P2C2: Speleothem Records of Permafrost and Climate from an Ice-Proximal, Mid-Continent Cave

该项目的总体目标是：1）使用洞穴（洞穴沉积物）中碳酸盐滴液特征的放射性铀-钍测年法确定威斯康星州南部土丘洞穴（CoM）过去的永久冻土条件; 2）通过测量洞穴沉积物中氧的稳定同位素比率，建立CoM水文气候条件的代用记录。具体的项目目标是：1）使用铀-钍定年法确定CoM在过去25万年的冻土发展时间; 2）使用氧同位素化学评估同一时间段的水文气候条件; 3）检查CoM在无冰和近冰环境中高频水文气候变化的幅度;和4）的方法永久冻土目前覆盖了北方约25%的陆地表面，是陆地有机物的重要汇carbon.对未来的气候预测表明，全球平均气温将大幅上升，在高纬度地区将被放大，并可能通过永久冻土融化期间释放更多的碳来启动积极的气候反馈。 限制永久冻土对大气温度升高的敏感性的一种方法是通过地质记录。大多数北美的古冻土重建来自地貌特征，但这些记录并不能提供冻土和/或气候条件的连续记录。该研究项目旨在重建古冻土的年代学，并记录过去25万年来LIS终端边缘附近的水文气候。 CoM在提供北美古环境记录方面处于独特的地位，该记录还测量了区域水文气候对冰川与间冰期条件的敏感性。潜在的更广泛影响包括支持一名女研究生和两名早期职业研究人员，利用与华盛顿大学地质博物馆的联系进行外联工作，开发样品制备和成像技术教程该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The general aims of this project are to: 1) determine, using radiometric Uranium-Thorium dating of carbonate drip-features in the cave (speleothems), when past permafrost conditions occurred at Cave of the Mounds (CoM) in southern Wisconsin; and 2) develop a proxy record of hydroclimate conditions at CoM by measuring stable isotope ratios of oxygen in the speleothems. Specific project objectives are: 1) determining the timing of permafrost development at CoM over the past 250,000 years using Uranium-Thorium dating; 2) evaluating the hydroclimate conditions over this same interval using oxygen isotope chemistry; 3) examining the amplitude of high-frequency hydroclimate variability at CoM during ice-free and ice-proximal settings; and 4) measuring the duration and magnitude of hydroclimate changes across known abrupt climate transitions.Permafrost presently covers approximately 25 percent of the land surface in the northern hemisphere and represents a significant sink of terrestrial organic carbon. Climate projections into the future indicate a significant increase in global average temperatures that will be amplified at high latitudes and could initiate a positive climate feedback through the release of additional carbon during permafrost thaw. One way to constrain the sensitivity of permafrost to warming atmospheric temperatures is through the geologic record. Most paleo-permafrost reconstructions in North America are derived from geomorphic features, but these records do not provide continuous records of permafrost and/or climate conditions. This research project aims to reconstruct the chronology of paleo-permafrost and produce a record of hydroclimate over the past 250,000 years near the terminal margin of the LIS. The CoM is in a unique position to provide a North American paleoenvironmental record that also measures the sensitivity of regional hydroclimate to glacial versus interglacial conditions.The potential Broader Impacts include support for a female graduate student and two early career researchers, leveraging connections with the UW Geology Museum for outreach efforts, developing tutorials for sample preparation and imaging techniques (e.g. fluorescent imaging), and using the open-source, freeware, to collate imaging and geochemical data.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.