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，在地方和全球范围内对社会和生态系统产生影响。因此，随着变暖力量记录和预测降水和极端事件的变化，了解水文循环如何对气候变化做出反应是至关重要的。然而，气候变暖对蒸发量的影响更难预测，如果没有蒸发期，就无法限制完整的水量收支。通过利用保存在湖泊沉积物中的各种现有的代用品，可以追踪过去的降水和温度，但很少有代用品可以记录蒸发量。该项目将通过开发一组被称为高度支化异戊二烯(HBI)的生物产生的有机化合物的使用来帮助填补这一空白。这些HBI是由硅藻产生的，应该包含硅藻居住的湖水的化学信号。该项目将通过一系列基于现场的现代校准，重点研究HIBI和蒸发信号之间的这种联系，并将这些校准应用于最近的湖泊沉积物档案，以测试它们再现蒸发的能力。这项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。通过更全面地低估水文循环的演变，可以保障国家的健康、繁荣和福利。这个与伍斯特学院合作的项目将为本科生提供研究机会，同时为加州大学研究生培养指导技能和经验。位于俄亥俄州的布朗斯湖现场将用于帮助学生在伍斯特大学的暑期项目期间获得野外和实验室经验，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。该项目将为研究生提供项目设计、数据合成、解释和传播方面的培训。这项研究还将通过在辛辛那提北区农贸市场开展实践活动，增加更广泛的公众对气候变化的知识和认识。该项目将促进利用氢同位素重建湖泊蒸发，从而有助于理解过去的水文平衡。具体地说，这项工作将把硅藻衍生的高度分枝的异戊二烯类化合物(HBI)作为古水文学的替代品。如果HBI的氢同位素记录了湖水的氢同位素，那么，当与其他替代指标相结合时，可以产生过去的湖水蒸发记录，以约束整个水文循环。为了实现这一目标，该项目将首先调查硅藻生长环境、水化学和HBI合成时间如何影响HBI的氢同位素组成。硅藻HBei将从一套水化学(即pH值、盐度)不同的湖泊的远洋和底栖生境中收集，因为这会影响硅藻的种类组成。HBI生产的季节性时间将通过在两年多的时间里从俄亥俄州东北部的布朗湖收集双月沉积物陷阱样本来确定。一旦解决了对HBI氢同位素的这些控制问题，该项目将确定沉积物档案中HBI氢同位素对当地水气候已知变化的敏感性。这将通过检查已有蒸发和降水记录的湖泊沉积物中的HBI来完成。这里提出的HBIS的发展将提供选址标准和必要的校准信息，以使用HBIS的氢同位素作为湖泊水蒸发的替代，最终改善从湖泊沉积物中重建古水文。该项目的广泛影响将通过以下方式造福社会：1)与主要是本科生的伍斯特学院建立合作伙伴关系，为本科生创造研究经验，促进这里提出的研究；2)为本科生创造一个独特的机会，让他们在课堂之外获得高级和关键的研究技能，并为他们在地球科学或STEM领域的职业生涯做好准备；3)除了指导学生加强教育和职业发展外，还为研究生和本科生提供项目设计、数据合成、解释和传播方面的培训；4)通过支持和培训博士生，以及支持本科生的培训，鼓励STEM吸纳和增加妇女人数；以及5)在辛辛那提北区农贸市场以地球科学实践活动的形式进行公共宣传，这是一个独特的场所，有助于增加更广泛的公众对气候变化的知识和认识。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.