My research interests fall under three main themes:
(1) Glacial-Interglacial & Millennial-Scale Carbon Cycle Dynamics: I am interested in the mechanisms responsible for changes in atmospheric CO2 concentrations on glacial-interglacial and shorter timescales. More specifically, I focus how ocean circulation impacts carbon sequestration and storage in the deep ocean.
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 , 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 Bølling-Allerød 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 siteճ 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 Ward, 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.
(2) Climate and Ocean Circulation Variability across Abrupt Climate Events: Much of what we know about modern climate cycles, such as the El Niño-Southern Oscillation, comes from historical observations from the last ~150 years. The limited length of these records prohibits us from fully understanding how these cycles will change in the future under continued greenhouse warming. I am interested in creating high-resolution records of climate and ocean circulation variability across past abrupt climate events to serve as an analog for future warming.
Current Project: Reconstructing ENSO Variability across Abrupt Climate Events over the last 70kyr: .
The El Niño/Southern Oscillation phenomenon is the largest natural interannual signal in the Earth's climate system and has widespread effects on global climate that impact millions of people worldwide. A series of recent research studies predict an increase in the frequency of extreme El Niño and La Niña events as Earth's climate continues to warm. In order for climate scientists to forecast how ENSO will evolve in response to global warming, it is necessary to have accurate, comprehensive records of how the system has naturally changed in the past, especially across past abrupt warming events. This project is split into two goals: (1) to understand differences in ENSO variability between the Holocene, Last Glacial Maximum, and Marine Isotope Stages 3 and 4, and (2) to look at higher resolution snapshots of ENSO variability over abrupt climate events, including the YD, BA, H1 of the last deglaciation, and multiple Heinrich events, stadials, and interstadials of the last glacial period. To do this, we are reconstructing thermocline temperature variability, a parameter integrally linked to ENSO, using a sediment core from the Eastern Equatorial Pacific. I am utilizing novel ICP-MS methods to analyze single foraminifera shells of N. dutertrei, a thermocline dwelling foraminifera, for Mg/Ca ratios. This project is part of an ongoing collaboration with Matthew Schmidt (ODU), and Tom Bianchi of the University of Florida. The Bianchi lab is utilizing biomarkers to reconstruct upwelling variability over the same events.
(3) Paleo Proxy Development and Refinement - The interface between modern oceanographic observations and paleoceanographic proxies: I am interested in how oceanographic parameters, such as temperature and salinity, are recorded in marine sediments. To this end, I go out to sea to collect seawater samples and newly deposited sediments from the ocean floor to examine the relationship between the chemical composition of the seawater and the sediments. I am also interested in how marine sediments are altered as they descend through the water column and are deposited on the sea floor, by processes like dissolution. I employ multi-proxy and multi-species approaches to help understand the recording depths of temperature proxies.
Current Project: Utilizing Multi-Species Foraminiferal Mg/Ca Paleothermometry to Track Changes in the TEX86 Export Depth in the Eastern Equatorial Pacific across the Last Deglaciation
Current Project: Refining the seawater δ18O – salinity relationship of the North Atlantic Ocean:
Seawater samples were collected in a latitudinal transect from the North Atlantic down to the Equator in an effort to establish regional relationships in the δ18OSW – salinity to better reconstruct δ18OSW in the past through combinations of formainiferal calcite δ18O and Mg/Ca temperature measurements.