OSE Ph.D. Defense: Tyler Vollmer

Title: Last Glacial Maximum Oxygen and Preformed Phosphate Reconstructions and its Linkage to Atmospheric CO2 Drawdown and Ocean Circulation

Date/Time: Thursday November 9 @ 2pm

Room Number: Ford ES&T 1177

Virtual Link: https://gatech.zoom.us/j/5365614544?pwd=WXRPc0NUNjM0WGZjNkNJRTlETnBmdz09

Abstract: 

During the Last Glacial Maximum (LGM), atmospheric CO2 was significantly lower than the pre-industrial, potentially due to an increase in the biological pump efficiency. Oxygen and preformed phosphate reconstructions can provide insight to changes in the biological pump efficiency. Many qualitative shallow/intermediate waters record higher O2 during the LGM due to an increase in oxygen solubility. Contrastingly, the qualitative oxygen proxies record lower O2 in deep waters during the LGM, potentially indicating this increased storage of respired carbon. In chapter 1, we quantified preformed phosphate and preformed δ13C of LGM bottom waters using a compilation of published paleo-temperatures, nutrient, and oxygen estimates from benthic foraminifera. Our results show that preformed phosphate of the Pacific and Indian deep oceans was reduced by about −0.53 ± 0.13 μM and suggest that much (64 ± 28 ppmv) of the Glacial-Interglacial CO2 drawdown resulted from changes in the ocean's biological pump efficiency. In chapter 2, we updated the first quantitative oxygen proxy, Δδ13C – O2, calibration from 6 cores to over 30 cores, providing increase confidence in this proxy. Using this updated calibration, we generated an oxygen, phosphate, and preformed phosphate depth profile in the South Indo-Pacific and Eastern Equatorial Pacific.  From the  paired oxygen and phosphate reconstructions, we show no significant changes in ocean circulation or productivity in the South Pacific or evidence of other deep water formation sites in the Pacific Ocean during the LGM.  Lastly, in chapter 3, we generated an oxygen profile in the Southeast Atlantic, where the Benguela upwelling oxygen minimum zone exist, showing a weakening and a downward shift of the oxygen minimum zone during the LGM. 

Committee Members:

Jean Lynch-Stieglitz

Takamitsu Ito

Christopher Reinhard 

Kevin Haas 

Joseph Montoya