Doctoral Dissertation Research: The Geographic Extent of Late Pleistocene Subsurface Ocean Warming in the Northern Atlantic Ocean Basin and the Origin of Heinrich Events

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This doctoral dissertation research project will examine the triggering mechanisms of Heinrich events, which are a widely recognized expression of abrupt global climate change. Heinrich events are interpreted as massive discharges of icebergs calved from the Laurentide Ice Sheet, the ice mass that covered a large share of the North American continent during the last ice age. The climatic context of Heinrich events was global in scale. Identifying these events therefore is an integral part of millennial-scale global climate change. The physical processes that triggered these events remain poorly understood, however. This doctoral dissertation research project will develop high-resolution records of North Atlantic Ocean subsurface water temperature bracketing known Heinrich events using magnesium-to-calcium ratios in seafloor-dwelling organisms in order to evaluate an external triggering mechanism for Heinrich events attributed to changes in oceanic circulation. This approach will employ a new analytical method for Mg-Ca paleothermometry on seafloor-dwelling organisms. Analysis of one ocean sediment core raised from the outer Labrador Sea basin suggested that bottom-water temperatures warmed before stratigraphic signatures of Heinrich events at that core location. Replication and further assessment of the geographic distribution of this pattern is necessary in order to establish its role as a forcing mechanism of Heinrich events. Exploratory data from the Reykjanes Ridge and the Labrador Sea have shown that the ocean sediment cores targeted for this project at the depths and locations of interest contain Heinrich event signatures and material necessary in order to carry out this project's research goals.The study of abrupt ice sheet destabilization and oceanic change has significant implications for future climate. Confirmation that intermediate-depth ocean warming played a significant role in triggering past ice-sheet instabilities will provide critical insights into potential future behavior of similarly configured Antarctic ice-sheet sectors. The project could provide validation for ice-sheet models currently being developed for projections of land-ice loss and attendant sea level rise. The project also will yield new data to test the accuracy of a new accessory developed by the doctoral student for use with plasma mass spectrometers in order to more effectively measure Mg-Ca paleothermometry in marine sediments. The project should improve understanding of the response of ice sheets to current and possible future changes in ocean circulation and temperature, factors which are among the greatest causes for concern and uncertainty in projections of sea-level rise. As a Doctoral Dissertation Research Improvement award, this project will provide support to enable a promising student to establish an independent research career.