Collaborative Research: Identifying basin-specific controls on isotopic and chronological offsets of lake sediment leaf wax hydrogen isotope records

为了确定未来的降水如何变化，重要的是要有一个过去降水变化的基线。然而，在产生仪器记录之前确定过去的降水仍然具有挑战性，并且需要使用保存在地质记录中的降水代用物。生物指标，如叶蜡，在这方面有希望，因为叶蜡的氢同位素组成主要反映降水的氢同位素组成。因此，保存在湖泊沉积物中的叶蜡是关于降水和水循环如何随地质时间变化的高分辨率信息的潜在来源。然而，现代叶蜡向湖泊沉积物的转移似乎引入了氢同位素值的抵消。该项目将有助于确定这些偏移量并确定控制它们的因素，从而可以改进过去水文条件的重建。在对这些抵消进行评估并测量其影响之前，沉积叶蜡与降水之间的定量联系将仍然有限。确定这些因素将有助于选择这些抵消影响最小的湖泊。这对于在仪器记录之前限制过去的水文变化至关重要，并将有助于预测未来的水文变化。该项目将通过与以本科生为主的圣劳伦斯大学的跨学科合作，为本科生创造教育和研究经验，从而造福社会。这将通过为本科生提供研究和培训经验来提高STEM领域的保留率，以培养先进的研究技能，扩大科学理解，并加强研究生学习或在地球科学领域的职业生涯的准备。最后，这项研究将通过扩大与辛辛那提博物馆中心（一个大型城市文化机构）合作的博物馆展览，促进更广泛的公众对地球科学的理解和对科学研究的欣赏。对过去的降水进行量化仍然是一个挑战。生物代用物，如叶蜡，在这方面有希望，因为叶蜡的氢同位素组成主要反映植物源水（即降水）。然而，从降水氢同位素组成推断出的定量古水文，由于对控制植物叶蜡的来源、整合和从植物到沉积物的运输的埋藏过程了解不足而受到限制。该项目将解决我们对湖泊沉积物叶蜡的理解中的两个重要空白。首先，研究人员将确定植被邻近如何影响湖泊沉积物中的叶蜡氢同位素信号。其次，他们将确定通过河流侵蚀对旧叶蜡的改造对湖泊沉积物中叶蜡的表观年龄的影响有多重要。本项目在美国纽约州阿迪朗达克山脉的温带湖泊中考察了这两个过程。研究方法将包括森林清查、现代叶蜡（正构烷烃和正构烷烃酸）分子和同位素（氢、碳）表征、湖泊沉积物取样和定年（210Pb、137Cs、14C），以及湖泊沉积物、集水区土壤和河流悬浮沉积物中正构烷烃的特定化合物放射性碳分析。该项目将通过以下方式造福社会：1)与以本科生为主的圣劳伦斯大学（St. Lawrence University）建立伙伴关系，发展跨学科合作和本科生研究机会，创造研究生指导机会，并为本科生提供实践同位素研讨会；2)通过每年为两名本科生提供研究和培训经验，提高STEM领域的留存率，以培养先进的研究技能，扩大对科学的理解，并为研究生学习或在地球科学领域的职业生涯做好准备；3)通过支持一名博士生和一名本科生，增加STEM领域的女性人数；4)提供指导，促进本科生和研究生的教育和职业发展，并通过定期评估和专业发展提高指导方法的成功率；5)通过与大型城市文化机构辛辛那提中心博物馆合作，扩大博物馆展览，促进公众对地球科学的更广泛理解和对科学研究的欣赏。

To determine how future precipitation might change, it is important to have a baseline of how precipitation changed in the past. However, determining past precipitation, prior to the generation of instrumental records, has remained challenging and necessitates the use of precipitation proxies that are preserved in the geologic record. Biological proxies, such as leaf waxes, hold promise in this regard as the hydrogen isotopic composition of leaf wax primarily reflects that of precipitation. Therefore, leaf waxes preserved in lake sediments are a potential source of high resolution information about how precipitation and the water cycle have changed over geologic time. However, the transfer of modern leaf waxes to lake sediments appears to introduce offsets in hydrogen isotope values. This project will help define these offsets and identify the factors that control them, thus allowing for improved reconstructions of past hydrological conditions. Until these offsets are evaluated, and their influence measured, the quantitative link between sedimentary leaf wax and precipitation will remain limited. Identification of these factors will allow selection of lakes where the effects of these offsets are minimal. This is critical for constraining past changes in hydrology prior to the instrumental record and will help anticipate future hydrologic change. This project will benefit society by creating educational and research experiences for undergraduates through interdisciplinary collaborations with St. Lawrence University, a primarily undergraduate institution. This will improve STEM field retention by providing research and training experiences for undergraduate students to develop advanced research skill sets, expand scientific understanding, and strengthen preparation for graduate studies or a career in the geosciences. Finally, this research will promote a broader public understanding of the geosciences and appreciation of scientific research by expanding on museum exhibits in collaboration with the Cincinnati Museum Center, a large urban cultural institution.Past precipitation remains a challenge to quantify. Biological proxies, such as leaf waxes, hold promise in this regard as the hydrogen isotopic composition of leaf wax primarily reflects plant source water (i.e., precipitation). However, quantitative paleohydrology, as inferred from precipitation hydrogen isotopic composition, is limited by a poor understanding of the taphonomic processes governing the source, integration, and transport of leaf waxes from plants to sediments. This project will address two significant gaps in our understanding of lake sediment leaf waxes. First, the investigators will determine how vegetation proximity influences leaf wax hydrogen isotope signals in lake sediments. Second, they will determine how important reworking of older leaf waxes via fluvial erosion impacts the apparent age of leaf waxes in lake sediments. This project examines these two processes in temperate lakes in the Adirondack Mountains, NY, USA. Research methods will include forest inventorying, modern leaf wax (n-alkane and n-alkanoic acid) molecular and isotope (hydrogen, carbon) characterization, lake sediment coring and dating (210Pb, 137Cs, 14C), and compound-specific radiocarbonanalyses of n-alkanes in lake sediments, catchment soils, and fluvial suspended sediments. The project will benefit society by 1) establishing partnerships with St. Lawrence University, a primarily undergraduate institution, to develop interdisciplinary collaborations and undergraduate research opportunities, create graduate student mentoring opportunities, and provide a hands-on isotope workshop for undergraduates; 2) improving STEM field retention by providing research and training experiences for two undergraduate students per year to develop advanced research skill sets, expand scientific understanding, and strengthen preparation for graduate studies or a career in the geosciences; 3) increasing the number of women in STEM fields by support of a Ph.D. student and an undergraduate students; 4) providing mentoring to enhance the educational and career development of undergraduate and graduate students, and improving the success of mentoring approaches through regular assessment and professional development; and 5) promoting broader public understanding of the geosciences and appreciation of scientific research by expanding on museum exhibits in collaboration with the Cincinnati Museum of Center, a large urban cultural institution.