Emergence of an anthropogenic salinity signal in the IndoPacific

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Temperature changes in the Indian and Pacific Oceans have profound impacts on distant societies, ecosystems, and economies. The El Niño Southern Oscillation (ENSO) is a clear example. ENSO can cause temperature changes that prompt large shifts in global weather. It can influence heatwaves, droughts, floods, and storms. Despite the significance of the IndoPacific, it is still not clear how this region will respond to rising greenhouse gases. Climate models agree that human-caused climate change will alter global temperature and rainfall patterns. However, climate models often disagree on the magnitude and even the sign of those changes. Another challenge to understanding climate change in the IndoPacific is that internal variability can mask trends. Long records from the tropical oceans are essential to untangle this uncertain response, but few instrumental exist. This project develops new ways to evaluate climate change in the data-sparse regions of the IndoPacific. Coral data can provide information about past temperature and hydrological conditions. This project will synthesize centuries of data from corals, instrumental observations, and climate models. These data will be used to reconstruct climate variability. Reconstructions of temperature, salinity, and precipitation will be compared with climate model simulations. This research will bolster scientific understanding of the tropical hydrological cycle response to climate change. Finally, this work will support an early career scientist, a graduate student, and undergraduate researchers. This project will evaluate the emergence of an anthropogenic signal in the tropical IndoPacific by leveraging long, seasonally-resolved tropical coral records with instrumental observations in an offline paleoclimate data assimilation (paleo-DA) framework. The proposed work will utilize novel methods to synthesize diverse sources of data (paleoclimate proxies, reanalysis products, isotope-enabled models, large ensembles, paleo-DA) to evaluate the range of internal variability and changes in temperatures, salinity, and precipitation variability from the 18th-century to the present. In particular, this work seeks to fill a critical data gap linking sea surface salinity to coral oxygen isotopic records (d18Ocoral) and coral-derived reconstructions of the oxygen isotopic composition of seawater (d18Osw) at seasonal to multidecadal timescales. This project aims to rigorously quantify uncertainties related to using coral d18O and coral-derived d18Osw to examine historic hydroclimate change and to establish best practices for inferring relationships with sea surface salinity at a variety of timescales. Interpretation of the timing, magnitude, and spatial patterns associated emergence of an anthropogenic signal in the coral-derived reconstructions will be contrasted with CMIP6 Large Ensemble historical and anthropogenically forced simulations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.