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Dryad

Local physical oceanographic and oxygen isotopic observations at Palmyra Atoll of the 2014-15 and 2015-16 El Nino events

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Sep 14, 2023 version files 306.73 MB

Abstract

Paleoclimate reconstructions of El Nino/Southern Oscillation (ENSO) behavior often relies on oxygen isotopic records from tropical corals (δ18O). However, few reef-based observations of physical conditions during El Nino events exist, limiting our ability to interpret coral δ18O. Here we present physical and geochemical measurements from Palmyra Atoll (5.9N, 162.1W) from 2014-17, along with a data assimilation product using the isotope-enabled Regional Ocean Modeling System (isoROMS). Coral δ18O signals are comparably strong in 2014-15 and 2015-16; notably, over 50% of the signal is driven by seawater δ18O, not temperature. If a constant seawater δ18O: salinity was present, this would imply a comparable salinity anomaly during both events. However, salinity changes are much larger during 2014-15, indicating a highly nonstationary relationship. isoROMS then shows that advection strongly influences δ18O during both the 2014-15 and 2015-16 El Nino, driving differences in the salinity/seawater δ18O relationship. This demonstrates the need for considering ocean dynamics when interpreting coral δ18O.