Three-dimensional Overturning Circulation Generated by Topography in the
Southern Ocean and Its Implications
Abstract
The Southern Ocean plays a major role in the global air-sea carbon
fluxes, with some estimates suggesting it takes up 40% of the total
anthropogenic carbon dioxide. Understanding the Southern Ocean
overturning transport is particularly important because the overturning
transport fluxes tracers between the depth and the surface. Recent work
shows that this vertical transport preferentially occurs downstream of
bottom topography, but there is further work to understand how this
relates to the theory of overturning circulation. This study uses an
idealized Southern Ocean-like MITgcm channel and particle tracking in
the thickness-weighted circulation to develop a new understanding of the
three dimensional-nature of the overturning. This study evaluates the
overturning transport by splitting the flow into three main driving
forces behind the transport. First, is a wind-driven Ekman transport
which is spread out throughout the domain and only leading order in the
upper overturning cell, although not entirely zonally-symmetric due to
the meandering nature of the flow. The remaining two components are
standing eddies and transient eddies both of which are localized near
the topography. The existence of the ridge weakens the response of the
overturning to changes in wind, especially in the lower cell. The
localization of the vertical flow shows the necessity of careful
modeling of these specific regions in the Southern Ocean to understand
the transport and carbon export.