One of the most pressing questions in the projection of future climate change is the issue of whether the variability of climate depends on the average state of the climate system. A large part of this question involves the behavior of the El Nino/Southern Oscillation phenomenon: for example, do El Nino events become stronger and more frequent as the climate warms? This project will address this question by developing a record of ENSO and tropical Pacific climate that spans the last 6,000 years - a period characterized by known changes in the seasonality of solar radiation. These reconstructions will test whether the ENSO system was forced by these solar radiation changes and if so, how and when changes occurred. To reconstruct ENSO behavior, the skeletal composition of ~12 fossil corals that were collected on the beaches of several of the Line Islands in the central tropical Pacific (Palmyra, Fanning and Christmas Islands) will be dated using U/Th techniques and analyzed with monthly resolution for their stable isotope and elemental composition. Previous research has shown that the skeletal chemistry of modern corals in this region captures a monthly-resolved record of ENSO with a fidelity that is on par with instrumental observations. Preliminary data suggest that the fossil coral geochemistry has not been altered, it is comparable to modern corals, and the ages of the fossil coral samples are characterized by a continuum of ages less than 6,000 years old. The broader impacts of this research will be invaluable to climate modelers seeking to improve the understanding and prediction of climate variability and the project will support graduate and undergraduate student training. This study also has socio-political impact that is related to the broader issues of climate change and global warming.
