Residual Overturning Circulation and Its Connection to Southern Ocean Dynamics

Madeleine Youngs, Ph.D., 2020
Glenn Flierl, Advisor

Recently, understanding of the meridional overturning circulation has improved, but primarily in a zonally-averaged framework. I have shown that the complexity of meanders, storm tracks, and other zonal asymmetries is necessary to reproduce the behavior of the overturning circulation. First I examined the role of basin width for whether the Atlantic or Pacific Oceans experience deep convection. I used models in combination with scaling laws to find that the transport is relatively weaker in the wider basin, priming it for convection shut-down. In addition, I examined the Southern Ocean using a hierarchy of models to understand the role of topography. I tested the response of the stratification and transport in the Southern Ocean to changes in wind using a two-layer quasi-geostrophic model. I find that meanders are necessary to reproduce the behavior of the Southern Ocean and that winds concentrate the baroclinic and barotropic instabilities downstream of the topography. Next, I investigated a primitive-equation Southern Ocean-like channel and examined the three-dimensional circulation to understand where there is upwelling. I found that the vertical transport happens primarily near topography. Finally, I added a biogeochemical model and found that carbon fluxes are enhanced near topography, again highlighting the role of zonal asymmetries.