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My research interests fall under three main themes:
(1) Glacial-Interglacial Carbon Cycle Dynamics: I am interested in the mechanisms responsible for changes in atmospheric carbon dioxide concentrations on glacial-interglacial timescales.
Current project: The Role of the Biological Pump in Deglacial CO2 Rise:
The initial trigger for atmospheric CO2 rise during Heinrich Stadial 1 remains elusive. Explanations often invoke the Southern Ocean release of carbon stored in the glacial abyssal ocean. Proxy records of abyssal circulation, however, lack evidence for variability coincident with the initial CO2 rise, inconsistent with a Southern Ocean driver. An alternate explanation for CO2 rise during Heinrich Stadial 1 involves the effect of a weakened Atlantic Meridional Overturning Circulation on the ocean's biological pump. In a recent publication, my coauthors and I tested this alternate hypothesis by compiling paired records of surface and intermediate-depth foraminiferal δ13C. Surface ocean δ13C decreased across Heinrich Stadial 1 while intermediate-depth δ13C increased, leading to a reduction in the upper ocean δ13C gradient. Our compilation also suggests that the δ13C gradient increased during the Bolling-Allerod and decreased again during the Younger Dryas. The Heinrich Stadial and Younger Dryas data are consistent with reduced biological export of isotopically light carbon from the surface ocean and its remineralization at depth. Our results support the idea that a weaker Atlantic Meridional Overturning Circulation decreased biological pump efficiency by increasing the overall fraction of preformed nutrients in the global ocean, leading to an increase in atmospheric CO2.
I have an active research project in the southeast Atlantic Ocean utilizing sediment from ODP Site 1087A in the Cape Basin to create additional paired records of surface and intermediate-depth foraminiferal δ13C. The surface ocean δ13C signal in this region is more complicated due to the site’s location in an upwelling zone. I am using micropaleontological methods to examine how temporal variability in upwelling can affect the surface ocean δ13C signal.
Current project: Constraining the Glacial Respired Carbon Pool in the Eastern Equatorial Pacific:
I am working with Brian Close, an MS student in the Department of Ocean, Earth, and Atmospheric Sciences at Old Dominion University on a project aimed at understanding the spatial extent of the glacial respired carbon pool in the Eastern Equatorial Pacific Ocean. We are utilizing the B/Ca proxy in benthic foraminifera to reconstruct bottom water carbonate ion concentrations over the last 90 kyr. High sediment accumulation rates and a tightly constrained age model for sediment core 17JC will allow us to examine changes in the respired carbon pool on millennial timescales.
Current project: Millennial-scale Variability in Sources and Sinks of Atmospheric CO2 from the Eastern Equatorial Pacific
The Eastern Equatorial Pacific is currently one of the largest natural sources of CO2 to the atmosphere, with variations due to the El Niño-Southern Oscillation. However, preliminary studies have suggested that the region may have been a sink for atmospheric CO2 during the last deglaciation. Working with Lenzie Warner, an undergraduate research scholar in the Department of Ocean, Earth, and Atmospheric Sciences at Old Dominion University, we are utilizing the B/Ca proxy in planktic foraminifera to reconstruct changes in surface water carbonate ion concentrations over the last glacial period. This will allow us to determine time periods over the last 90 kyr when this region may have been either a source or sink for CO2, and compare them with records of productivity from the same sediment core. Ultimately, we hope to link changes in productivity in the Eastern Equatorial Pacific to time periods when the region was either a source or sink for CO2.