Vegetation refugia and warm pulses amid late Eocene cooling and drying on the margins of East Antarctica
Abstract
The Eocene-Oligocene Transition (EOT), ~33.7 Ma, is marked by a 1.5‰ increase in the ẟ18Obenthic record associated with the glaciation of Antarctica, with that and an earlier ice surge at 37.3 Ma detected in the eNd of fish teeth. In this study, sediment cores from Prydz Bay, Ocean Discovery Program (ODP) Legs 119 and 188, are revisited for biomarker and microfossil evidence for Antarctic terrestrial climate across 36 to 33 Ma. Both before and after the EOT, pollen counts were dominated by reworked taeniate grains produced mostly by Glossopteridales and eroded from Permian strata in the Prydz Bay catchment. Contemporaneous pollen assemblages indicate Nothofagus-Podocarp forests with spikes in pollen abundance coinciding with warming at 35.7 and 34.7 Ma. Lipid biomarkers switch between branched and isoprenoid tetraethers (the BIT index) revealing the balance between terrestrial and marine inputs in marginal settings. When the BIT index is high we employ the BayMBT calibration to reconstruct land temperatures and find cooling from 15 to 10°C. When the BIT is low, we obtain BAYSPAR TEX86-based estimates that suggests ocean temperatures cool from 13 to 10°C. These temperatures support plant community refugia, even as the ice sheet surged to the ocean influencing ocean Nd geochemistry at 37.3 Ma and across the EOT at 33.7 Ma. As plants persist, we can use plant waxes to reconstruct hydrological conditions on land associated with hydroclimate changes leading up to and across the ice advance. The ẟ13C of the plant wax C30 n-alkanoic acids show a 2.3‰ positive shift indicating drying accompanied cooling. The ẟD of the same plant waxes saw an increase of 17-19‰ associated with the 35.7 and 34.7 Ma warming intervals consistent with expected T-dD relationships. At the EOT, a D-enrichment in seawater of up to 6‰, can explain part of the 25‰ observed D-enrichment in plant wax, as well as a more restricted coastal, lowland vegetation source as ice advances. Together the new pollen and biomarker evidence add to multi-proxy interpretations and reveal dynamic conditions in Prydz Bay hydroclimate and erosion in the lead up to the EOT.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMPP0240018T
- Keywords:
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- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 3337 Global climate models;
- ATMOSPHERIC PROCESSES;
- 1655 Water cycles;
- GLOBAL CHANGE;
- 4914 Continental climate records;
- PALEOCEANOGRAPHY