The Localization by Topography of the Three-Dimensional Overturning
Circulation of 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 contributes to up to
40\% of the oceanic anthropogenic carbon dioxide uptake,
despite only comprising 20\% of oceanic surface area.
Thus the Southern Ocean overturning transport, the circulation that
transports tracers between the surface and the interior, is particularly
important for climate. Recent studies show 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 and localized
nature of the overturning, splitting the flow into three main drivers of
the transport. The first component is a wind-driven Ekman pumping into
or out of a density layer; it is primarily but 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. Localization of the vertical flow shows the necessity
of careful modeling these specific regions in the Southern Ocean to
understand the transport, carbon export, and the connection with the
oceans to the north.