Numerical Modeling of the Greenhouse-Icehouse Transition: Eocene-Oligocene Boundary

EAR-0652020

KUMP

Currently available numerical models are inadequate for the study of the most important events in the history of the biosphere. One such event is the major transition from Greenhouse to Icehouse conditions at the Eocene-Oligocene boundary ~34 million years ago, with the first establishment of a large ice sheet on Antarctica and other worldwide climate reorganizations. Such events have taken place over time scales of a few hundred thousand to millions of years, and are inherently time continuous, with drastic changes in long-term components (e.g., ice sheets, CO2) depending on and feeding back on the current state of short-term quasi-equilibrium components (atmosphere, upper ocean). Box models of global biogeochemical cycles are useful for studying long-term evolution of the oceans, atmosphere and biota, while coupled ocean-atmosphere general circulation models are ideal for studying a few equilibrium states and decadal to centennial climate change. However, none of these tools is able to simulate important long-term events and transitions of interest with adequate spatial and temporal resolution to provide testable predictions.

Intellectual Merit. This project will combine long-term biogeochemical components with newly available coupling techniques developed for long-term physical climate modeling, to perform the first spatially and temporally resolved biogeochemical investigation of the Eocene-Oligocene transition. The coupling techniques involve a matrix look-up table of A/OGCM solutions and asynchronous driving of a 3-D ice sheet model, developed by R. DeConto and D. Pollard in other NSF-funded projects. The biogeochemical components have been developed and used extensively by L. Kump and collaborators, and include 2-D land weathering and OGCM biogeochemistry. Recently J. Zachos and L. Kump have applied box-model versions of these components through several million years spanning the E-O transition. They found that biogeochemical feedbacks can have important interactions with the physical climate system, resulting in post-Transition overshoots and million-year oscillations as observed in benthic -18O records. Using the new coupling techniques and 2-D/3-D models, we will test five specific hypotheses concerning events leading up to, during and after the E-O transition. We will compare and validate results against extensive and temporally resolved paleoceanographic data, augmented by terrestrial proxies: - Benthic oxygen and carbon isotopic records constraining bottom-water temperatures plus ice volume, mean ocean isotopic composition and deep basin gradients; - Mg/Ca records for temperature; - Sequence stratigraphic records on passive margins further constraining sea level; - Geologic constraints on atmospheric CO2; - Proxies for terrestrial weathering intensities, rates, and inputs to the ocean.

Broader Impacts. One undergraduate (doing her senior thesis) and one graduate student will be involved in this research, with .the undergraduate focusing primarily on one of our hypotheses concerning shelf-basin partitioning of carbonate deposition. We will facilitate the dissemination of numerical modeling expertise by holding a summer workshop at Penn State during the funding interval of this project, sponsored by the Worldwide Universities Network (WUN;wun.ac.uk). The theme of this first WUN-SIES/TA workshop will be on modeling and data interpretation in deep-time studies, primarily for graduate students, postdocs, and early-career Earth science professionals. L. Kump has been instrumental in WUN-sponsored activities at Penn State, including monthly video seminars, graduate student exchanges and workshops. Through WUN, students involved in this project will have the opportunity to travel to Southampton (UK) to work with their climate modeling group.