Offshore Export of Glacial Water and Ice in an Eddying Ocean

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A popular hypothesis in climatology posits that the discharge of large amounts of water from continental glaciers and ice sheets ("glacial water") into the North Atlantic may disrupt ocean circulation and cause climate change. Implicit in this hypothesis is that the glacial water would spread away from the coast, as a buoyant (light) surface layer, and decrease the density of surface waters in the open ocean at high latitudes. In turn, the formation of deep dense waters and the attendant northward flux of heat would be reduced. In this project, a computer model of ocean circulation, with unprecedented spatial resolution, will be used to study the pathways of glacial water discharged into different oceanic regions along eastern North America. The model will simulate small-scale eddies and will be coupled to an iceberg model, so that the ability of various oceanic processes to transport meltwater and icebergs seaward could be tested. This project will promote the progress of science by elucidating the contribution of various oceanic phenomena to the offshore export of glacial water in both liquid and solid forms. It will be profitable to the scientific community by (i) informing the design of glacial water perturbation experiments performed with coarse-resolution climate models which cannot explicitly represent small-scale eddies in the ocean, (ii) constraining the interpretation of seafloor and sediment core observations which suggest that deep-keeled icebergs moved southward along the western North Atlantic margin and that glacial meltwater intruded recurrently beyond the continental shelf during the last 30,000 years, and (iii) sharing experimental results via open-access web sites. This project will support education by engaging a Graduate Student and three Undergraduate Students. The Graduate Student will be exposed to the capability of modern ocean circulation models to study dynamical phenomena of climatic relevance. The three Undergraduate Students will conduct laboratory experiments of freshwater discharge with rotating turntables and make the video footage of the experiments available on-line. A how-to manual will be written and linked to the footage, so scientists, teachers, and students could repeat the experiments. Finally, this project will benefit society by (i) providing a better assessment of the potential of both past and future glacial water discharges to cause climate change, and (ii) serving as a template for future model studies on the impact of icebergs on offshore shipping activities and oil/gas exploration in high-latitude waters.In more technical terms, over the course of this project, a coupled ocean circulation-iceberg model with submesoscale resolution will be developed and used to produce detailed simulations of the evolution of glacial water entering the ocean along eastern North America in liquid and solid forms. The specific objectives of this project are (i) to test the role of different dynamical phenomena in the offshore export of glacial water from the Laurentide Ice Sheet (LIS), which occupied North America the last (de)glacial periods, (ii) to develop a parameterization of glacial water export for use in coarse-resolution climate models, and (iii) to yield constraints on the interpretation of seafloor observations and sediment records from the eastern North American margin in terms of glacial water discharges from the LIS. To meet these objectives, a model with kilometer-scale or higher resolution will be applied in regional domains. The work plan of this project includes three tasks. (1) A numerical model of ocean circulation will be configured to represent two oceanic regions in the western North Atlantic: the Grand Banks of Newfoundland, and the Middle Atlantic Bight including the oceanic region near Cape Hatteras. (2) The circulation model will be coupled to an iceberg model. (3) Experiments with the coupled model will be conducted to elucidate the roles of three processes in the seaward export of glacial water: coastal current separation near the Grand Banks, transport by shelfbreak eddies in the Middle Atlantic Bight, and entrainment with the Gulf Stream near Cape Hatteras.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.