Did Deep Waters Form at High Latitudes During the Late Cretaceous Greenhouse?

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This three-year project will investigate oceanic heat transport during climate intervals of extreme overall warmth and high atmospheric greenhouse gas concentrations. Such 'greenhouse' climate states are characterized by equator to pole thermal gradients significantly lower than the modern. Flatter meridional temperature gradients imply enhanced poleward heat transport either via oceanic or atmospheric circulation. The research team will establish the composition of intermediate and deep waters in the Southern Ocean to test the hypothesis that deep waters formed in high latitude regions during greenhouse climates. Determining where deep waters formed and how they circulated is necessary for evaluating the role of the deep oceans in poleward heat transport and maintenance of low equator to pole thermal gradients characteristic of globally warm climates. The team selected the Atlantic/Indian sector of the Southern Ocean as a starting point for global reconstruction of middle to Late Cretaceous intermediate- and deep-water composition to address the issue of whether deep waters formed at low latitudes (warm, saline deep waters) or high latitudes during periods of extreme warmth. Presently available stable isotope records do not permit determination of deep-water provenance or circulation patterns, however, recent model simulations suggest that large-scale convection of deep waters occurred in the Southern Ocean and North Pacific during the Late Cretaceous. The team will determine the composition of intermediate- and deep-water masses during late Cenomanian to late Campanian (95-75 Ma) by generating records of the Neodymium isotopic composition of fossil fish debris from Deep Sea Drilling Project (DSDP) and ODP Sites in the targeted region. In addition, Nd isotope analyses of well-preserved planktic foraminifera will provide insight into deep-water provenance and changes in weathering inputs to the Southern Ocean. Strontium isotope data from fish teeth will provide age-control in the two sites lacking biostratigraphic age control.Intellectual Merit: The research provides a means of assessing the nature of deep-sea circulation during one interval of greenhouse climate and of increasing understanding of the larger role of meridional overturning circulation in global heat redistribution during greenhouse climate intervals. Project results contribute to numerical models of past climates that provide estimates of rates and magnitudes of climate change through geologic time.Broader Impacts: Undergraduate and graduate students are integral to the research activities. Students are involved in sample preparation, data acquisition and interpretation, and may publish results in peer-reviewed, scientific journals and participate in professional meetings. Students from groups traditionally under-represented in the geosciences are targeted for participation with assistance from diversity programs at Texas A&M University. The project will enhance the career of a young female geoscientist, as well as help to perpetuate the legacy of the Deep-Sea Drilling Project and Ocean Drilling Program. The research results are integrated into education and outreach activities. Indirect benefits to society include contributions made to understanding climate variations during periods of greenhouse climate conditions.