HR: 10:50h
AN: PP52B-03    [Abstracts]
TI: The Isotopic History of Western North American Grasslands
AU: * Crowley, B E
EM: bcrowley@pmc.ucsc.edu
AF: University of California, Santa Cruz, Department of Anthropology 1156 High st., Santa Cruz, CA 95064, United States
AU: Koch, P L
EM: pkoch@pmc.ucsc.edu
AF: University of California, Santa Cruz, Department of Earth and Planetary Sciences 1156 High st., Santa Cruz, CA 95064, United States
AB: Over the last 20 years, researchers have detected a rise in carbon isotope values of fossil mammals, paleosol minerals, and organic substrates roughly 6 to 8 Ma, which indicates an increase in the relative abundance of C4 grass at localities around the world. Prior research has shown that this increase in C4 abundance did not occur in cool high latitude regions, nor did it occur at sites around the Mediterranean. Similarly, modern California and Nevada do not support native C4 grasses. These states have a water regime similar to the Mediterranean region, with hot and dry summers, and most precipitation occurring during the cool winter months. Because the amount of C4 grass in North American ecosystems correlates positively with growing season temperature, it is not surprising that these western states, which have a winter growing season, do not support C4 plants. This does not necessarily imply, however, that C4 plants have never been favored in these western states. We used the carbon isotope composition of fossil ungulate tooth enamel as a proxy for C4 plant abundance in California and Nevada from 18 Ma to the present. Our carbon isotope data suggest that whereas there are very few native C4 species living in California or Nevada today, C4 plants may have been present in the region as early as the Late Miocene. Furthermore, there is an indication that C4 plants may have increased in abundance in the region during Pleistocene glacial periods.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1055 Organic and biogenic geochemistry
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4914 Continental climate records
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting