RAPID Collaborative Research: Ground Truthing Coral Proxy Reconstructions of ENSO by Observing the 2014-15 El Nino

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The El Nino/Southern Oscillation (ENSO) is the dominant source of inter-annual climate variability in the world and it impacts a variety of important economic sectors in the U.S. and around the world like fisheries, agriculture and water resource management. Thus, it is vital to understand how its properties (magnitude, rate of occurrence, duration) might change under future climates. State-of-the-art climate model projections show no agreement on the direction of future ENSO changes and instrumental records are too short to constrain the statistics of ENSO, making it imperative to use paleoclimate reconstructions to establish a long-term observational context for ENSO. Record of isotopic oxygen in corals collected in the central equatorial Pacific suggests that ENSO may strengthen in the future, but a major caveat remains: the physics of the ENSO influence on the properties of corals is poorly understood, as their chemical composition is affected by water exchange in the reef environment, as well as by precipitation. This project will collect in situ observations of physical conditions (temperature, salinity,and currents) and isotopic variations (in seawater, precipitation, and corals) during a rapidly approaching event: the El Nino expected during winter 2014-15. The proposed dataset will be used to validate ongoing modeling work, create a reanalysis of the 2014-15 El Nino event with the goal of improving the interpretation of reconstructed records of past El Ninos. A post-doctoral fellow will lead the project and in the process will expand her technical and scientific expertise.Tehcnical description: Paleoclimate information from coral isotopic oxygen (Oxygen 18) is a critical source of data on past climate variability, providing an observational baseline for projections of future changes to ENSO. However, ENSO affects Oxygen 18 through advective shifts, topographically-induced upwelling, and surface fluxes: this makes it extremely difficult to use Oxygen 18 records for quantitative comparisons with instrumental records or climate model output. An ongoing NSF-funded study using a newly developed, isotope-enabled version of the Regional Ocean Modeling System (isoROMS) has shown that the spatial scale of processes affecting Oxygen 18 may be quite small, as proxy collection sites lie in nearshore reef environments. Thus, obtaining additional in situ data is critical for validating the isoROMS result and improving dynamical understanding. The El Nino event expected during winter 2014-15 provides a unique opportunity to collect both in situ physical oceanographic information and isotopic measurements, which combined with the isoROMS work would provide the most complete and dynamically consistent characterization of the El Nino influence on proxy sites to date. The results would greatly advance interpretation of existing oxygen 18 records as well as climate model validation efforts. The proposed dataset would be a major asset for studies of coral paleoclimate reconstruction as well as climate model validation. This project is led by an early career female scientist, and will add an observational component to the research she is conducting under an NSF Ocean Sciences postdoctoral fellowship. Collaborations with colleagues from a range of disciplines will be facilitated by this study. Finally, the results will be used to develop a reanalysis of the 2014-15 El Nino event, which will be provided as a resource for the community.