Antarctic Peninsula Dried Up During the Late Eocene

Declining moisture availability on the Antarctic Peninsula during the Late Eocene

Authors:

1. Kathryn W. Griener (a)
2. David M. Nelson (b)
3. Sophie Warny (a)

Affiliations:

a. Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA 70803

b. University of Maryland Center for Environmental Science, Appalachian Laboratory, Frostburg, MD 21532

Abstract:

Paleobotanical data have indicated that the Antarctic landscape shifted from a beech (Nothofagus)-dominated forest to a more sparsely vegetated taiga-like woodland and tundra during the Late Eocene, coincident with progressive cooling and glacial growth. Reduced moisture availability may have contributed to this vegetation change, but there is limited evidence for assessing the Late Eocene hydrologic regime. We evaluated the relationship between Nothofagus δ13C and moisture availability by determining δ13C of modern Nothofagus pollen, sporopollenin, and leaves and comparing these results to precipitation data. To assess plant moisture availability and vegetation composition just prior to the Eocene-Oligocene boundary, we measured δ13C of fossil Nothofagus sporopollenin (Nothofagidites) from the SHALDRIL 3C cores (which date to ~ 35.9 My) and evaluated these results in the context of temporal variation in pollen assemblages from the same sediments. Values of carbon isotope discrimination (∆) for modern Nothofagus sporopollenin range between 18.1 and 22.4‰. These values are positively correlated with precipitation amount, as well as pollen and leaf ∆, which suggests that fossil sporopollenin ∆ records the level of plant moisture availability. ∆ values obtained from Nothofagidites sporopollenin from the SHALDRIL 3C sediments range between 17.9 and 20.2‰ and generally decline through time. These results suggest a decrease in plant moisture availability on the Antarctic Peninsula during the Late Eocene, perhaps as a result of declining precipitation and/or soil moisture. Therefore, moisture stress experienced by Nothofagus likely contributed to the shift to a more sparsely vegetated Late Eocene landscape. Our results show that carbon isotopic analysis of pollen from C3 plants may aid understanding how variations in moisture availability contribute to shifts in plant community composition in the paleorecord. Keywords: Nothofagus, Nothofagidites, Antarctica, moisture availability, Eocene, δ13C