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

University Of California-Irvine, Irvine CA

Investigators

Abstract

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.