Fossil Coral Estimates of Tropical Pacific SST and Hydrological Variability During the Last Millennium

The response of tropical Pacific climate to anthropogenic forcing remains uncertain, in large part because global climate model projections are poorly constrained by available instrumental climate data from this key region. A growing body of evidence suggests that the tropical Pacific may have cooled in response to higher solar irradiance during the Medieval Climate Anomaly (MCA; 900-1200AD), consistent with the response of an intermediate complexity model of tropical Pacific climate. However, such a paradigm fails to explain dramatic centennial-scale shifts in tropical Pacific hydrology recorded in some key proxy records. Indeed, model and theoretical constraints suggest that tropical Pacific SST and hydrology are key diagnostic indicators of large-scale dynamical responses to external radiative forcing, but high-resolution, quantitative reconstructions of tropical Pacific SST and hydrology are scarce. With the proposed research, we will generate multiple monthly-resolved, multi-proxy reconstructions of central tropical Pacific SST and hydrology from modern and fossil corals in four intervals of the last millennium: the MCA, the 14th century, the Little Ice Age (1500- 1800AD), and the late 20th century. Our research strategy is designed to deliver quantitative uncertainty estimates for each reconstruction, with a heavy emphasis on reproducibility and on quantifying the potential impacts of geochemical alteration on the paleo-reconstructions. The coral-based reconstructions will be compared to millennium-long global climate model simulations conducted as part of the upcoming Climate Model Intercomparison Project (CMIP5), with the goal of assessing the relationship between centennial-scale changes in central tropical Pacific SST and hydrology and external radiative forcing.