Collaborative Proposal -- Eocene Climate Record of Seymour Island: The Environmental Context for Ecological and Evolutionary Change

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This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, provides funds for a study to investigate paleoenvironmental conditions during the Eocene on Seymour Island, Antarctica. The cooling trend that began with early Eocene peak warmth and culminated in the growth of permanent ice sheets on Antarctica in the early Oligocene marks the most significant interval of climate change in the Tertiary, both because of its magnitude and the effects it had on the composition, diversity and ecology shelf faunas. Seymour Island on the Antarctic Peninsula provides a unique setting within which the interplay between changes in climate and environment can be directly related to the concurrent evolution of invertebrate macrofaunas. Because of its high southern latitude location, the Paleogene sedimentary sequence at Seymour Island may record the timing of the onset of cooling, and the magnitude of that change through time, more precisely than less sensitive lower latitude sites. In addition, because the succession is highly fossiliferous, patterns of change in the diversity and ecology of invertebrate communities can be directly evaluated within this context of environmental change. The evolution of these high latitude shelf faunas during the Paleogene is especially important as they may represent the source of diversification for many southern hemisphere warm water faunas. Richard Aronson (Dauphin Island Sea Lab) and Daniel Blake (University of Illinois) have suggested that cooling during the Eocene had a profound affect on the ecology of shallow marine faunas at high latitudes. They hypothesize that cooling eliminated the shell-crushing predators that abound in warmer waters, thus lifting the predation pressure on the remaining molluscan fauna. In response, they predict that predation pressure by the shell drilling gastropods will show an increase through time, and that characteristic shell architectures that defend against shell crushers will show a decline. They are currently testing this hypothesis through a paleontological investigation of the Eocene La Meseta Formation on Seymour Island. However, to evaluate their hypothesis that cooling is the direct cause of ecological change, it is critical that a temperature history be assessed independently and tied directly to their documented patterns of predation. This project will work collaboratively with Aronson and Blake to generate a high-resolution temperature curve for the Eocene section on Seymour Island. This record will be derived from the d18O values of shell carbonate from several bivalve, gastropod, and brachiopod taxa sampled from the identical horizons used for their paleoecologic study. Possible offsets among co-occurring taxa (vital effects) will be quantified through intensive sampling of multiple taxa within shell beds to ensure that a meaningful composite, long-term record can be assembled. Replicate samples for each available taxon will be collected from each sampling horizon, so that variability within time horizons can be accommodated when assessing the magnitudes of change observed throughout the Eocene. Samples for isotope analysis will be collected under this project while working as a member of Aronson and Blake's field team. This will ensure that the records of temperature and faunal change are explicitly linked. Such an integrated approach will provide a more complete understanding of the evolutionary and ecological effects of cooling on the Antarctic ecosystem, and offer insight into the response of faunas to global climate change.