Abstract
Atmospheric river (AR) storm events are primary drivers of seasonal precipitation and flooding in Northern California but remain poorly constrained in the isotopic record. The ratio of stable oxygen isotopes 18O/16O is a common marker for describing the progress of precipitation event in a quantifiable way. The identification of such a signal may contribute to the continued study of how AR storms progress and the relationship of their frequency and severity to inter-annual climate patterns such as the El Nino-Southern Oscillation and further study of their signal in paleoclimate records. A series of 61 storm events were sampled from a single location in Northern California between 2018 and 2021. Each sample was analyzed spectroscopically with a Liquid Water Isotope Analyzer and attributed to a storm event. Each event was analyzed using varied parameters of integrated vapor transport (IVT), integrated water vapor (IWV), duration, and source location to make determinations on the storm’s severity and its qualification as an AR or non-AR. AR storms were found to be more depleted than non-ARs by 0.46 ‰. Overall, storms were more frequent during ENSO positive phases, and storms which occurred in ENSO positive phases were 1.19 ‰ less depleted than storms occurring in ENSO-negative phases, suggesting a strong correlation between δ18O of meteoric water and ENSO phase. Those storms greatest in severity and duration were tropical in origin and many underwent a pattern of “re-enrichment” in which initial δ18O values were anomalously low and subsequent values higher than expected. A mechanism of consistent feeding over the course of severe ARs is proposed to explain this deviation.