HR: 17:45h
AN: PP34A-08    [Abstracts]
TI: Linked Paleosol and Model-based Reconstructions of Paleoprecipitation During Episodes of Extreme Global Warmth: Early Eocene and Middle Cretaceous Greenhouse States Compared
AU: * White, T S
EM: tswhite@essc.psu.edu
AF: Earth and Environmental Systems Institute, 2217 EES Building The Pennsylvania State University, University Park, PA 16802 United States
AU: Pollard, D
EM: pollard@essc.psu.edu
AF: Earth and Environmental Systems Institute, 2217 EES Building The Pennsylvania State University, University Park, PA 16802 United States
AB: The late Paleocene-early Eocene Earth has been characterized as having ice-free poles inhabited by mammals, reptiles and deciduous forests, with globally averaged surface temperatures 2-4§C greater than today. This episode is considered to have been the warmest of the Cenozoic and is perhaps second only to the middle Cretaceous greenhouse as a period of extreme global warmth during the past 100 million years. This study focuses on an oxygen isotopic record of paleoprecipitation derived from early Eocene paleosol siderite spherules obtained along a paleolatitudinal transect from Texas to Alaska, though data obtained from coeval deposits in France, Spain and Australia are considered. The data are used to benchmark a stable isotope tracer version of the GENESIS v. 2 general circulation model and are compared to similar paleosol-model results for the middle Cretaceous Earth. The early Eocene oxygen isotope profile displays a pronounced south to north depletion, an observation that is very similar to a transect of middle Cretaceous paleosols; both profiles are depleted relative to similar modern latitudinal distributions. These results indicate that early Eocene paleotemperatures may have been as warm as those reconstructed for the middle Cretaceous and provide evidence for an amplified atmospheric hydrologic cycle during these episodes of extreme warmth. Our modeling results support these conclusions and indicate that early Eocene and middle Cretaceous Precipitation minus Evaporation (P-E) profiles were substantially altered compared to modern profiles: in tropical and middle latitude regions, P-E values are 2-3X greater than today, whereas in the subtropics, P-E values are up to 3X less than today. Some worst-case climate model scenarios predict future temperatures similar to those hind cast for the middle Cretaceous greenhouse state. However, most researchers conclude that middle Cretaceous climate reconstructions are irrelevant to considerations of near-term climate change due to substantial differences between Cretaceous and modern land-sea distributions. We submit that the overall geographic similarity between the Paleocene-Eocene and modern worlds as well as the similarity between our Cretaceous and Eocene climate reconstructions suggests that the reconstructions may be meaningful as potential worst-case scenarios for Earth's globally-warmed climate future. Our reconstructions further suggest that substantial shifts in the distribution of precipitation can be anticipated under conditions of extreme greenhouse warmth.
DE: 9604 Cenozoic
DE: 9609 Mesozoic
DE: 1040 Isotopic composition/chemistry
DE: 1620 Climate dynamics (3309)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting