Applied Mathematics Seminar | Xiaoting Yang, Three-dimensional structure of mid-depth Meridional Overturning Circulation: a study on the dynamics and paths of the Ocean Deep Eastern Boundary Currents

MC 5501

Speaker

Xiaoting Yang, University of California San Diego

Title

Three-dimensional structure of mid-depth Meridional Overturning Circulation: a study on the dynamics and paths of the Ocean Deep Eastern Boundary Currents

Abstract

The Meridional Overturning Circulation carries significant transports of mass, carbon, heat and other important tracers in the global ocean, and it has a rich three-dimensional structure. Southward Deep Eastern Boundary Currents (DEBCs), between one and four kilometers depth in the Southern Hemisphere basins, are important branches of the overturning circulation by contributing to large-scale ocean transport and determining mid-depth tracer distribution patterns. However, these currents have remained under-appreciated for their roles in global circulation and their dynamics were not well understood. The vorticity dynamics of such currents are studied in a hierarchy of models in this work. Realistic and idealized regional GCM experiments robustly show that these DEBCs are governed by a layered-structure of vorticity dynamics: a wide layer dominated by “interior-like” vorticity balance, plus a narrow hydrostatic layer adjacent to the eastern boundary. This means that DEBCs are dynamically different from the well-known western boundary currents. It is further shown that the dominant vortex stretching term is maintained by both eddy temperature transport and sloping bathymetry. How the DEBCs contribute to meridional large-scale ocean transport is studied from a Lagrangian perspective as well. DEBCs, along with the deep western boundary currents, and mid-depth interior flows, are found to be important branches carrying mid-depth mass transport southward towards Drake Passage.