Collaborative Research: Tracking North Atlantic Water Column Structure and Circulation Through the Late Cretaceous Using Oxygen and Neodymium Isotopes in Fish Debris

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This project will investigate circulation of intermediate and deep water masses in the Late Cretaceous North Atlantic relative to organic carbon burial and greenhouse ocean circulation. The Late Cretaceous includes the warmest conditions and the largest perturbations to global carbon cycle of the past 250 million years. Our pilot data (epsilon-Nd and d18O values in fish debris) suggest a separate and distinct, locally-sourced intermediate water mass was present in the tropical western North Atlantic throughout the Late Cretaceous except during regional to global carbon burial events, specifically, ocean anoxic event 2 and the mid-Cenomanian event. During these intervals there are dramatic shifts in epsilon-Nd that suggest enhanced bottom water mixing. The combination of evidence for 1) sinking of waters at low latitudes as a background condition and 2) more vigorous deep circulation during times of global burial of organic carbon contradict predictions of leading paradigms regarding both greenhouse oceans and ocean anoxic events. This project will test the generality of these findings through analyses of well-dated samples from a variety of sites using Ocean Drilling Program/Deep Sea Drilling Program cores. By mapping the distribution of intermediate and deep water waters as a function of position, depth, and time we will both constrain the importance of deep water in the evolution of greenhouse climates and provide empirical results against which ocean-atmosphere climate models can be compared. The project involves a new partnership between state universities and includes key participants who are members of groups underrepresented in the Earth Sciences.