A PRELIMINARY ANALYSIS OF THE PRECIPITATION STABLE ISOTOPE SIGNATURE OF THE RECENT 2023-24 SUPER EL NIÑO

The El Niño-Southern Oscillation (ENSO) is on of the largest modes of climate variability and has major impacts on the hydroclimate of the western US. However, there is much uncertainty about ENSO and its associated impacts on western US hydroclimate will respond to rising atmospheric CO2. The geologic record of past, warmer intervals provides an opportunity to examine the response of ENSO to higher CO2. Much of our record of the role of ENSO in modifying western US hydroclimate during past warm intervals comes from the oxygen isotopes (δ18O) of meteoric water preserved in authigenic minerals in sedimentary units. Thus, interpreting these records in terms of the role of ENSO requires knowledge of how ENSO modifies precipitation δ18O today. We took advantage of the 2023-24 super El Niño to sample precipitation at 19 distinct locations across the western US to characterize how ENSO modifies precipitation δ18O. We compare our preliminary results with expected precipitation δ18O using the Online Isotopes in Precipitation Calculator, which estimates the modern precipitation δ18O at a given site using elevation and geographical coordinates as input. Additional work will characterize how ENSO modifies precipitation Δ'17O, which is more sensitive to humidity and evaporation than δ18O. Ultimately, our work will help refine our understanding of how signals of ENSO are transmitted through the hydrologic system and encoded into the geologic record.