PhD Dissertation Defense: Barbara Zemskova

The PhD Dissertation Defense of Barbara Zemskova will be presented by the University of North Carolina at Chapel Hill Department of Marine Sciences and Institute of Marine Sciences. The main location of this event will be in seminar room G201 on the ground floor of Murray Hall on UNC main-campus in Chapel Hill, NC. The defense will be streamed live to room 222 of UNC’s Institute of Marine Sciences in Morehead City, NC. This event will be held on Monday, November 5th at 11:00 am.

Title: Ocean energy budget analysis: from large scale circulation to submesoscale instabilities

Abstract: The Meridional Overturning Circulation (MOC) in the ocean plays an important role in transporting heat and nutrients, supplying oxygen to the deep ocean, and sequestering atmospheric carbon below the mixed layer. The MOC is believed to be driven by surface wind stress, heat and freshwater fluxes, tides, and other energy sources, though the degree to which each of these source terms contributes to the MOC dynamics is poorly understood. To study the interplay between surface wind and buoyancy forcing, an Available Potential Energy (APE) framework is applied to data from a global ocean model ECCO2 and a regional ocean model for the Southern Ocean (SOSE). This framework allows for partitioning of the energy budget into mean and turbulent components of the kinetic and available potential energy reservoirs and decompose adiabatic (processes without heat or matter transfer) and diabatic (processes with irreversible transfer of heat or matter) portions of the ocean circulation. While the ocean models incorporate realistic bathymetry and aspect ratios, the spatial and temporal resolutions are too coarse to resolve small scale dynamics, such that mixing and dissipation rates cannot be computed directly. To fully resolve all relevant scales, I conducted direct numerical simulations (DNS) of an idealized basin representation of the Southern Ocean and compared the ocean energy budget with the SOSE results. I find that while the Southern Ocean residual circulation is sensitive to the balance between the magnitudes of surface wind stress and buoyancy forcing, diapycnal mixing rates are primarily set by the dense water plume resulting from buoyancy loss near the pole. The comparison between the DNS and the ocean model SOSE also highlights that for the Southern Ocean interbasin transport and seasonal fluctuations are important to the basin energy dynamics and need to be incorporated into the future high-resolution studies of the Southern Ocean sensitivity to changes in surface forcing, such as greater heat and freshwater fluxes and stronger Westerlies.

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