Collaborative Research: Tapping an unused biomarker for insights of past evaporation

水文循环的变化，包括降水和蒸发，对地方到全球尺度的社会和生态系统都有影响。因此，了解水文循环如何响应气候变化是至关重要的，因为变暖力量记录并预测了降水和极端事件的变化。然而，变暖对蒸发的影响更难以预测，如果没有蒸发期，就无法限制完整的水分收支。利用湖泊沉积物中保存的各种现有代用物，可以跟踪过去的降水和温度，但记录蒸发的代用物很少。该项目将通过开发一组被称为高支异戊二烯类化合物（hbi）的生物产生的有机化合物来填补这一空白。这些hbi是由硅藻产生的，应该包含硅藻生活的湖水的化学信号。本项目将重点关注hbi与蒸发信号之间的联系，通过一系列基于实地的现代校准，并将这些校准应用于最近的湖泊沉积物档案，以测试它们重现蒸发的能力。本工作的目标是在时间和空间上推进蒸发重建，最终改善古水文重建和未来水文变化的预测。只有更全面地了解水文循环的演变，才能保障国家的健康、繁荣和福祉。这个与伍斯特学院的合作项目将为本科生提供研究机会，同时为加州大学研究生提供指导技能和经验。俄亥俄州的布朗斯湖野外场地将用于帮助学生在伍斯特大学的夏季项目中获得实地和实验室经验，该项目旨在从代表性不足的群体中招募STEM学生进入地球科学领域。这个项目将为研究生提供项目设计、数据综合、解释和传播方面的培训。这项研究还将通过在辛辛那提北部农贸市场开展动手活动，扩大公众对气候变化的认识和认识。该项目将推动利用氢同位素重建湖泊蒸发，从而有助于了解过去的水文平衡。具体来说，这项工作将考虑硅藻衍生的高支异戊二烯类（hbi）作为古水文代用物。如果hbi的氢同位素记录了湖泊水的氢同位素，那么，当与其他代用物相结合时，可以生成湖泊水蒸发的过去记录，以约束完整的水文循环。为了实现这一目标，本项目将首先研究硅藻生长栖息地、水化学和合成HBI的时间如何影响HBI的氢同位素组成。硅藻hbi将从水体化学（即pH值、盐度）不同的一系列湖泊的远洋和底栖生物栖息地收集，因为这会影响硅藻物种组成。HBI生产的季节性时间将通过在两年内从俄亥俄州东北部的布朗湖收集两个月的沉积物收集器样本来确定。一旦这些对HBI氢同位素的控制得到解决，该项目将确定沉积物档案中HBI氢同位素对当地水文气候已知变化的敏感性。这将通过检查湖泊沉积物中的hbi来完成，那里已经存在已确定的蒸发和降水记录。本文提出的hbi的发展将为利用hbi的氢同位素代替湖泊水分蒸发提供选址标准和必要的校准信息，最终改善湖泊沉积物的古水文重建。该项目的广泛影响将使社会受益：1)与伍斯特学院建立合作伙伴关系，伍斯特学院主要是本科院校，通过为本科生创造研究经验，进一步推进这里提出的研究；2)为本科生创造一个独特的机会，在课堂之外获得先进和关键的研究技能，并为他们在地球科学或STEM领域的职业生涯做好准备；3)为研究生和本科生提供项目设计、数据综合、解释和传播方面的培训，并指导学生加强教育和职业发展；4)通过支持博士研究生的培养，以及支持本科生的培养，鼓励STEM领域的女性参与并增加女性人数；5)在辛辛那提的北侧农贸市场开展地球科学实践活动，这是一个独特的场所，有助于扩大公众对气候变化的认识和认识。该奖项反映了美国国家科学基金会的法定使命，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。

Changes to the hydrological cycle, including precipitation and evaporation, have impacts on society and ecosystems at local to global scales. Therefore, it is critical to understand how the hydrological cycle responds to changes in climate as warming forces documented and projected changes in precipitation and extreme events. However, the effects of warming on evaporation are more challenging to anticipate, and without the evaporation term, the complete water budget cannot be constrained. By utilizing various existing proxies preserved in lake sediments, it is possible to track past precipitation and temperature, however there are few proxies that record evaporation. This project will help fill in this gap by developing the use of a group of biologically produced organic compounds called highly branched isoprenoids (HBIs). These HBIs are produced by diatoms and should contain a chemical signal of the lake water the diatoms live in. This project will focus on this connection between the HBIs and the signal of evaporation through a series of field-based modern calibrations and apply these calibrations to recent lake sediment archives to test their ability to reproduce evaporation. The goal of this work is to advance evaporation reconstruction both temporally and spatially, ultimately improving paleohydrologic reconstructions and future predictions of hydrologic change. The national health, prosperity and welfare can be safeguarded with a more complete understating of the evolution of the hydrological cycle. This collaborative project with The College of Wooster will provide research opportunities to undergraduate students while developing mentoring skills and experience for the UC graduate students. The Browns Lake field site in Ohio will be used in to help students gain field and lab experiences during summer programs at Wooster designed to recruit STEM students into the geosciences from underrepresented groups. This project will provide training in project design, data synthesis, interpretation and dissemination for graduate students. This research will also increase broader public knowledge and awareness of climate change by creating hands-on activities at the Northside Farmer’s Market in Cincinnati. This project will advance the use of hydrogen isotopes to reconstruct lake evaporation and hence contribute to the understanding of past hydrologic balance. Specifically, this work will consider diatom-derived highly branched isoprenoids (HBIs) as a paleohydrology proxy. If the hydrogen isotopes of HBIs record lake water hydrogen isotopes, then, when combined with other proxies, past records of lake water evaporation can be generated to constrain the complete hydrologic cycle. To accomplish this, this project will first investigate how diatom growth habitat, water chemistry, and timing of HBI synthesis influences the hydrogen isotopic composition of HBIs. Diatom HBIs will be collected from pelagic and benthic habitats across a suite of lakes that vary in water chemistry (i.e., pH, salinity), as this influences diatom species composition. The timing of seasonality of HBI production will be determined by collection of bimonthly sediment trap samples from Brown’s Lake in northeastern Ohio over two years. Once these controls on HBI hydrogen isotopes are addressed, this project will then determine the sensitivity of HBI hydrogen isotopes in sediment archives to known changes in local hydroclimate. This will be completed by examining HBIs in lake sediments where established records of evaporation and precipitation already exist. The development of HBIs proposed here will provide site selection criteria and necessary calibration information to use hydrogen isotopes of HBIs as a proxy for lake water evaporation, ultimately improving paleohydrological reconstructions from lake sediments. The project broader impacts will benefit society by 1) establishing a partnership with the College of Wooster, a primarily undergraduate institution, by creating research experiences for undergraduate students that will further the research proposed here; 2) creating a unique opportunity for undergraduate students to gain advanced and critical research skills, beyond the classroom, and preparing them for careers in the geosciences or STEM fields; 3) providing training in project design, data synthesis, interpretation and dissemination for graduate and undergraduate students in addition to mentoring students to enhance educational and career development; 4) encouraging the inclusion of and increasing the number of women in STEM by providing support for, and the training of the Ph.D. student, along with support for the training of undergraduate students; and 5) public outreach in the form of geoscience hands-on activities at the Northside Farmer’s Market in Cincinnati, a unique venue to help increase broader public knowledge and awareness of climate change.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.