Quantifying the Effects of Lower Sea Level on Tropical Pacific Climate during the Last Glacial Maximum

ACKNOWLEDGEMENTS First and foremost, I wish to thank my research advisor and co-advisor, Dr. Kim Cobb and Dr. Emanuele DiLorenzo. They have put a tremendous number of hours into this project while teaching me that conducting research is challenging, tiring, but more importantly, fun and inspiring. I also wish to thank Dr. Yen, both who introduced me to the world of academia. Working in both of these labs has paved a sturdy path for my plans for pursuing a doctorate as the next step in my life. I would also like to acknowledge my family, who have supported and motivated me to pursue what I enjoy. viii SUMMARY Global climate changes during the Last Glacial Maximum (LGM) have been ascribed to a combination of lower atmospheric CO 2 , increased albedo, large continental ice sheets, and altered ocean circulation. The effect of lowered sea level on LGM climate is typically considered negligible, despite the exposure of a continent-scale landmass, the Sunda Shelf, between Southeast Asia and Australia in the tropical Indo-Pacific. Paleoclimate records document profound changes in tropical Indo-Pacific climate during the LGM, including weaker ENSO (Tudhope et al, 2001), changes in the sea-surface temperature gradient along the equatorial pacific (Lea et al, 2000; Koutavas et al, 2002), and changes in western Pacific hydrology (Martinez et al 1997; Oppo et al, 2003). A recent investigation of coupled atmosphere-ocean general circulation model (AOGCMs) simulation of LGM climate suggests that the emergence of the Sunda Shelf alone may have reshaped tropical Indo-Pacific climate, contributing to a significant reduction in the strength of the Walker circulation (DiNezio et al, 2011). If true, this would have profound implications for the attribution of LGM paleoclimate signals of proxy data from the Indo-Pacific region. For example, regional drying inferred by a Sunda Shelf record during the LGM may be entirely ascribed to sea level change, and counter the regional hydrological response to cooler global temperatures and reduced pCO 2 during the LGM. The only modeling experiment that isolated the effects of lowered LGM sea level on climate documented significant atmospheric circulation changes spanning the entire tropical Pacific (Bush, et. al., 2003). Here we present the results of lowered sea level simulations with the AGCM SPEEDY (Molteni, 2003) designed to gauge the sensitivity of tropical Pacific climate to ix an LGM sea level drop of roughly 120m. Modifying the model's land/sea mask, we Sea and the Arafura …