Abstract
The strong influence of enhanced diapycnal mixing over rough topography
on bottom-water circulation is illustrated using results from two
global ocean model experiments. In the first, diapycnal diffusivity
is set to the observed background level of 10(-5) m(2) s(-1) in regions
not subject to shear instability, convection, or surface-driven mixing.
In the second experiment, mixing is enhanced above rough bottom topography
to represent the dissipation of internal tides. Three important results
are obtained. First, without the enhanced mixing in the abyssal ocean,
the deep North Pacific Ocean becomes essentially a stagnant basin,
with little bottom-water circulation and very weak deep stratification.
Allowing for the enhanced diapycnal mixing above rough bottom topography
leads to increased bottom-water circulation and deep stratification
and a potential vorticity distribution in the North Pacific that
is much more realistic. Second, the enhanced diapycnal mixing above
rough topography results in a significant intensification and deepening
of the Antarctic Circumpolar Current, as well as in stronger bottom-water
formation around Antarctica. Last, our experiments suggest that dissipation
of internal tides and the associated enhanced diapycnal mixing in
the abyssal ocean play no part in the circulation of deep water forming
in the North Atlantic Ocean and in the associated transport of heat
in the ocean.
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