Multiproxy Terrestrial Records of Climatic and Ecological Change During the Early Eocene Climatic Optimum.

Abstract

The Eocene (~56–34 million years ago) was a period of major global changes, and perhaps the most substantial of these changes occurred during the Early Eocene Climatic Optimum (EECO), a period of extreme global warmth that lasted for as much as 3 million years (53–50 million years ago). These warm conditions make the EECO an important period for understanding Earth’s climate system and its impact on the biosphere, as current projections of the future include many of the conditions experienced during the early Eocene. Problematically, few records of terrestrial conditions exist during this time period, so in order to address many of the outstanding questions about what the early Eocene may have looked like on land, this dissertation employs a multiproxy approach using a wide variety of terrestrial-based paleosol and geochemical techniques as well as carbon cycle modeling in order to constrain and explore the climatic and ecological conditions of the early Eocene. This dissertation introduces the EECO and the methods employed for expanding high-resolution terrestrial records during the event, presents the first high-resolution multiproxy record of the EECO on land from a site in the Green River Basin (southwest Wyoming), develops a new proxy for paleoprecipitation based on the magnetic properties of modern soils and applies this new proxy to the EECO, compares the Green River Basin record to new multiproxy record from the nearby Wind River Basin, presents a multiproxy record from the Southern Hemisphere (Salta Basin, Argentina), and finally develops a global carbon cycle model to test different causal mechanisms of the EECO based on the presented proxy data. Overall we find distinct similarities between temperate region responses in both hemispheres, and suggest that the transient nature and terrestrial conditions of the peak EECO are inconsistent with previously suggested causal mechanisms. This dissertation contributes to our understanding of different climate states, and attempts to explore both the causes of and terrestrial responses to major warming events in the past, while providing both new techniques for developing terrestrial records and a platform for more detailed spatial and temporal examinations of rapid climatic events and their causes.