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

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 (5.9◦N, 162.1◦W) 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/sea...