Distinct Controls on the Strength of the Abyssal Overturning Circulation: Channel versus Basin Dynamics
Journal
Journal of Physical Oceanography
Journal Volume
51
Journal Issue
7
Start Page
2073
End Page
2086
ISSN
0022-3670
1520-0485
Date Issued
2021-07
Author(s)
Jansen, Malte F.
Abstract
Although the reconfiguration of the abyssal overturning circulation has been argued to be a salient feature of Earth’s past climate changes, our understanding of the physical mechanisms controlling its strength remains limited. In particular, existing scaling theories disagree on the relative importance of the dynamics in the Southern Ocean versus the dynamics in the basins to the north. In this study, we systematically investigate these theories and compare them with a set of numerical simulations generated from an ocean general circulation model with idealized geometry, designed to capture only the basic ingredients considered by the theories. It is shown that the disagreement between existing theories can be partially explained by the fact that the overturning strengths measured in the channel and in the basin scale distinctly with the external parameters, including surface buoyancy loss, diapycnal diffusivity, wind stress, and eddy diffusivity. The overturning in the reentrant channel, which represents the Southern Ocean, is found to be sensitive to all these parameters, in addition to a strong dependence on bottom topography. By contrast, the basin overturning varies with the integrated surface buoyancy loss rate and diapycnal diffusivity but is mostly unaffected by winds and channel topography. The simulated parameter dependence of the basin overturning can be described by a scaling theory that is based only on basin dynamics.
Subjects
Abyssal circulation
Meridional overturning circulation
Ocean dynamics
Publisher
American Meteorological Society
Type
journal article