Date of Award
Campus Access Dissertation
Earth and Ocean Sciences
Robert C Thunell
The Eocene-Oligocene transition (EOT) is one of the largest global paleoclimatic events of the past 50 myr. Surface and deep water temperature histories and variations in global ice volume were reconstructed using paired measurements of δ18O and Mg/Ca on benthic and planktonic foraminifera across the EOT using Ocean Drilling Program (ODP) Sites 1090 and 1265. I identified A 2°C cooling of bottom waters coincident with the first shift in benthic foraminiferal δ18O (termed EOT-1), that suggests little, if any, change in global ice volume. A ~1.5°C cooling of bottom waters and simultaneous 0.75 δseawater increase associated the second benthic δ18O shift (termed Oi-1 for "Oligocene isotope event 1") is equivalent to a ~70 m eustatic drop and the growth of an ice sheet that is 85-95% of the modern Antarctic ice sheet. A 3°C sea-surface temperature warming at Site 1265 is found to be associated with Oi-1 that likely reflects restricted South Atlantic gyral circulation and/or a response to an increase in atmospheric pCO2. My data from Site 1265 and previous work at Site 1263 [Peck et al., 2010] show a significant Δδ18O surface-to-bottom water gradient that represents the development a well-stratified water-mass during Oi-1. Fossil fish teeth εNd data paired with benthic δ18O and δ13C records from ODP Sites 1090 and 1265 were used to reconstruct past episodes of glacial weathering and deep water circulation patterns associated with the EOT. A pulse of nonradiogenic εNd at Site 1090 occurs in conjunction with the benthic δ18O increase across Oi-1. A similar relationship at ODP Site 738 from Prydz Bay [Scher et al., 2011] argues for a pulse of eroded sediments from the Antarctic continent during ice-sheet growth. The rapid timing and coeval nature of the εNd shift at Sites 738 and 1090 suggests the dissolved material was quickly spread throughout the Southern Ocean and diluted by mixing with other water masses. There is also evidence for a pulse of Northern Component Water occurring immediately prior to the EOT based on an εNd decrease at Sites 1090 and 1265 that is coincident with an inter-basinal benthic δ13C gradient.
Pusz, A. E.(2011). Paleoceanographic and Paleoclimatic Changes Associated With the Eocene-Oligocene Transition. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/1340