RAPID: The effect of El Nino on delivery of organic carbon in the Santa Clara River, CA

厄尔尼诺-南方涛动(ENSO)导致热带东太平洋上空的风和海面温度发生变化。通常，这会导致南加州的降雨量高于平均水平。该项目旨在了解与ENSO相关的高降雨量如何影响碳从陆地向海洋的输送。具体地说，科学家们将评估在这些事件期间，从分水岭被侵蚀的土壤中提取的独特的老化碳池是否被输送到海洋中。颗粒和沉积有机碳的样本将从加利福尼亚州的圣克拉拉河收集。样本将在2023年12月至2024年4月期间在不同的河流流量条件下采集。将对这些样本的化学成分进行分析，并将其与以前在ENSO和非ENSO期间收集的样本进行比较。这套独特的样本将记录在不同的河流流动条件下，向海洋输送的碳的数量和来源是否存在差异。这项研究的结果将改善全球和长期对陆地向海洋输出碳的估计。该项目将支持一名早期职业科学家和一名为拉美裔服务的加州大学欧文分校的本科生。这项研究将研究在即将到来的2023-24年厄尔尼诺事件期间输送到南加州沿海地区的有机碳(OC)的来源。该项目将检验这一假设，即圣克拉拉河流域的极端降水会动员一个独特的矿物质伴生有机碳池，该池不同于在正常或低降水年份动员的有机碳。以往的研究表明，在1997年至1998年强厄尔尼诺期间被动员的矿物伴生有机碳的∆14C和d13C值高于在枯水期输出的有机碳。科学团队将在2023-2024年厄尔尼诺事件期间，在不同的流动条件下从圣克拉拉河收集颗粒态有机碳(POC)和沉积有机碳(SOC)样本。将测量整体有机碳的放射性碳(∆14C)和稳定碳同位素值(D13C)，以及正构烷烃的化合物特定同位素分析。这些数据将与降水和河流流量条件变化时期(1997-98年、2002-03年、2021-22年)获得的数据进行比较。这种同位素信息的组合将使科学家能够估计来自不同来源的有机质的相对贡献，以及与侵蚀矿物伴生的有机碳对沉积物的贡献。该项目将为加州大学欧文分校(UCI)的博士后和本科生提供研究和培训机会。UCI是一家为拉美裔服务的机构。博士后将参与清洁教育计划(气候、扫盲、赋权和质疑)，并设计基于现象的科学课程，供加州大学洛杉矶分校地球系统科学系的当地高中和本科生实验室使用。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。

El Niño–Southern Oscillation (ENSO) causes changes in winds and sea surface temperature over the tropical eastern Pacific Ocean. Typically, this results in above average rainfall in Southern California. This project aims to understand how high rainfall associated with ENSO influences the delivery of carbon from land to the ocean. Specifically, the scientists will evaluate whether a unique pool of aged carbon derived from eroded soils in the watershed is transported to the ocean during these events. Samples of particulate and sedimentary organic carbon will be collected from the Santa Clara River in California. The samples will be collected under different river flow conditions between December 2023 and April 2024. The chemical composition of these samples will be analyzed and compared to samples collected during previous ENSO and non-ENSO time periods. This unique set of samples will record whether there are differences in the amounts and sources of carbon delivered to the ocean under different river flow conditions. Results from this study will improve global and long-term estimates of carbon export from land to the ocean. This project will support an early career scientist and an undergraduate student at the University of California-Irvine, a Hispanic-serving institution.This study will examine the sources of organic carbon (OC) delivered to the coastal zone of Southern California during the upcoming El Niño event of 2023-24. The project will test the hypothesis that extreme precipitation in the Santa Clara River watershed mobilizes a unique pool of mineral-associated OC that differs from the OC that is mobilized during normal or low precipitation years. Previous studies have shown that the mineral-associated OC mobilized during the strong El Niño of 1997-98 had higher ∆14C and d13C values than the OC exported during low flow periods. The science team will collect particulate OC (POC) and sedimentary OC (SOC) samples from the Santa Clara River under different flow conditions during the 2023-2024 El Niño event. Radiocarbon (∆14C) and stable carbon isotope values (d13C) for bulk OC, and compound specific isotope analyses of n-alkanes will be measured. These data will be compared to data obtained during time periods when precipitation and river flow conditions varied (1997-98, 2002-03, 2021-22). This combination of isotope information will allow the scientists to estimate the relative contributions of organic matter derived from different sources as well as the contribution of eroded mineral associated OC to the sediments. The project will provide research and training opportunities for a postdoc and an undergraduate student at the University of California-Irvine (UCI), a Hispanic-serving institution. The postdoc will participate in the CLEAN Education Program (Climate, Literacy, Empowerment and iNquery) and design phenomenon–based science curricula for use in local high schools and undergraduate labs in the Earth System Science Department at UCI.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.