ABSTRACT

This proposal will support an attempt to reconstruct the position of the Intertropical Convergence Zone (ITCZ) during the last 2,000 years by measuring hydrogen isotope ratios in lipids from well-dated, rapidly accumulating sediments from freshwater, saline and hypersaline basins on 13 islands between 2°S and 10°N across the Pacific Ocean.

Despite convincing evidence from tree rings and mountain glaciers for a Medieval Warm Period 800-1300 A.D. and a Little Ice Age 1400-1850 A.D. in Northern middle latitudes, there is little known about the magnitude and geographic footprint of the climate changes associated with those events, especially in the tropics. Yet the tropics play a central role in the climate system owing to the massive fluxes of latent heat and moisture that emanate from there, and the possibility exists that mid-latitude climate anomalies of the last 2,000 years were caused or amplified by climate changes in the tropics. Whether passive responders or active players in these two events, initial results from this team suggest that tropical rainfall patterns underwent large changes during those episodes. Lipid hydrogen isotope data indicate that the Galapagos (1°S, 90°W) were wet, and both Washington Island (5°N, 160°W) and Palau (7°N, 134°E) were dry during the Little Ice Age compared to the modern and Medieval Warm Periods. The simplest interpretation of these findings is that the ITCZ was located south of its present mean position of ~7°N during the Little Ice Age. Drier than modern conditions in both the Galapagos and Washington Island during the Medieval Warm Period suggest that the ITCZ was positioned north of its present location at that time. In order to confirm these findings and gain a detailed understanding of Pacific ITCZ changes during the last 2,000 years, decadally-resolved lipid äD records from lakes and lagoons within, north and south of the modern ITCZ range, and removed from direct monsoonal and continental influences, are required. The Marshall and Gilbert Islands (15°N to 3°S, 162°E to 177°E) are ideal, spanning quasi-symmetric gradients of rainfall to the north and south of the ITCZ and having many suitable fresh and saline basins to core. Clipperton Atoll (10°N, 109°W) and Christmas Island (2°N, 157°W), along with the Galapagos, Washington Island and Palau provide the remainder of sites needed to reconstruct changes in the position of the ITCZ.

This project will support a female graduate student and facilitate the education of undergraduate students in environmental research. The proposed research will foster international collaborations with scientists and governments in several Pacific Island nations, France and Ecuador.

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