CONTINENTAL CLIMATE AND VEGETATION PATTERNS IN NORTH AMERICA AND WESTERN EURASIA BEFORE AND AFTER THE CLOSURE OF THE CENTRAL AMERICAN SEAWAY

Today, the Gulf Stream causes considerable warming of the middle and higher latitudes of Western Eurasia also mirrored by vegetation distribution. Under the maritime climate of Western Eurasia vegetation types with a more thermophilous aspect exist compared to the eastern part of North America at the same latitude. Currently, discussion on changes in Gulf Stream intensity is very active. A slowing-down or even complete cessation of the thermohaline circulation in the North Atlantic would have severe consequences for the regional climate and vegetation of Western Eurasia. The study of Cenozoic continental patterns evolving under a potentially reduced Gulf Stream intensity may provide important clues in this context.

Presently we study paleobotanical records from two transects in Western Eurasia and North America in order to reconstruct paleoclimate and vegetation patterns for a middle Miocene, late Miocene and late Pliocene time slice, each representing different boundary conditions concerning atmospheric CO2 and paleogeographical configuration. Quantitative paleoclimate data are obtained using the Coexistence Approach that can be applied on all types of sufficiently diverse fossil floras. Vegetation patterns and gradients are reconstructed using diversity of plant functional types such as evergreen or deciduous arboreal components. This procedure is also applicable on different types of plant organs and has a reduced taphonomic bias. Comparisons of both, proxy-derived vegetation and climate data obtained from different methods allows for obtaining a coherent reconstruction. For the Miocene where a reduced Gulf Stream intensity is assumed, our results point to milder conditions in Western Eurasia and to a more thermophilous aspect of the vegetation compared to the eastern part of North America. Now, a late Pliocene data set can be presented, representing the conditions after the closure of the CAS. Our studies complemented by model experiments testing the effect on Gulf Stream intensity on continental climate in both transects.

[grant: DFG MI 926 / 8-1]