Do Tropical Glaciations Record Heinrich Events?

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9422220 DORN Considerable debate has occurred in recent years regarding the dynamics of climatic change. Prevailing models have held that climates change gradually over periods of centuries. A growing body of evidence accumulated by Hartmut Heinrich and others indicates that changes may have been much more abrupt at various times during the last 70,000 years. Four so-called "Heinrich events" were characterized by the release of large numbers of icebergs into the North Atlantic from the Laurentide Ice Sheet covering northeastern North America. Fine debris carried by these icebergs have been found in cores of sediments from the bottom of the ocean. Correlative evidence of sudden climatic changes in other parts of the world has been found in terrestrial pollen accumulations, in glacial deposits, in lake fluctuations, and in marine corals and sediments. This research project will involve U.S. and Mexican scientists in an examination of glacial deposits on the slopes of Mauna Kea in Hawaii and the volcanoes of central Mexico. Both of these highlands near the Tropic of Cancer are known to have been glaciated during the period when Heinrich events occurred. Glacial deposits will be dated using a variety of high-precision dating techniques, including isotope analyses of 14-Carbon, 36- Chlorine, 3-Helium, and 21-Neon. This project will provide a detailed glacial chronology for these tropical highlands, and it will assist in reconstruction of transformations of soils, geomorphic systems, and biogeographic systems in nearby lowland areas. These data will advance consideration of the hypothesis that Heinrich events were global in character by assessing whether these rapid changes affected tropical highlands. The accumulation of evidence gathered through studies like this will contribute considerably to understandings of the dynamics, timing, and speed of global change.