Utilizing Present-Day Stable Water Isotopes to Improve Paleoclimate Records from the Southeast (USA)

Abstract:

Present-day water isotope data are used to help interpret climate (paleo-rainfall) proxies archived in the geologic record, which can then aid in the creation of General Circulation Models (GCM). The Southeast (USA) is under-represented with respect to present-day measurement of water isotopes and high-resolution paleoclimate records, thus GCMs must extrapolate data for the region. We will evaluate water isotope data (δ¹⁸O, δD) collected and analyzed at The University of Alabama (33°13'N, 87°33'W) since June 2005. The monitoring station, central to the Southeast, was established to provide long-term water isotope data needed for reconstructing paleo-rainfall records of the region.

Proxy data (e.g., δ¹⁸O_calcite) archived in speleothems have been demonstrated to provide trustworthy information about past climate conditions; however, present-day monitoring of both local rainfall and cave dripwater are crucial. The decade-long (June 2005 – May 2015) rainfall record allows for the establishment of the relationship between water isotopes (δ¹⁸O, δD) and monthly air temperature, rainfall amount, as well as the general differences between summer and winter rainfall. Dripwater from Cathedral Caverns (34°34'N, 86°13'W), located in northeastern Alabama, has been sampled at a monthly resolution since January 2015 to determine if the water chemistry in the cave represents an annual mean for the rainfall or if it is seasonally biased. The ultimate goal of this study is to better understand how atmospheric air currents (specifically the strength/position of the Polar Jet Stream, PJS), and hence rainfall in the Southeast, varied during past periods of relative warming (e.g., Dansgaard-Oeschger events) and cooling (e.g., Heinrich events) of the Northern Hemisphere atmosphere. Future GCMs will be improved if a reliable high-resolution paleo-rainfall record can be produced for the Southeast.