HR: 11:05h
AN: OS12B-04    [Abstracts]
TI: The power consumed by mixing processes in the deep-ocean interior
AU: * St. Laurent, L
EM: lous@ocean.fsu.edu
AF: Florida State University, Department of Oceanography, Tallahassee, FL 32309 United States
AU: Simmons, H
EM: hsimmons@iarc.uaf.edu
AF: University of Alaska - Fairbanks, International Arctic Research Center, Fairbanks, AK 99775 United States
AB: In the traditional view, the meridional overturning circulation of the ocean is assumed to close through diabatic processes in the ocean interior. In this scenario, mixing in the ocean interior acts to transfer heat from the temperate waters of the upper ocean to the coldest waters of the abyss. The upwelling of warmed abyssal waters balances the production of deep water occurring at high latitudes. The mechanical energy needed for this scenario has been estimated at 2 TW. In an alternate view, the meridional overturning cell is closed with only minimal mixing in the ocean interior. This adiabatic closure occurs largely through upwelling in the Southern Ocean. In this view, mixing is required for only the densest waters of the global ocean. A recent estimate suggests that only 0.5 TW of mechanical energy is needed for mixing these densest waters. We present an alternative estimate of the power consumed by mixing. Unlike the previous estimates, our calculation is independent of an assumed production rate of deep water. Instead, we start from estimates of the mixing rate, and assume a steady-state turbulent energy balance. We use global climatological data to estimate the power consumption by mixing in control volumes distinguished by their neutral density. Average diffusivity values, estimated in basin-scale hydrographic inversions, are also used for these calculations. We estimate the power associated with mixing between 30 S and 47 N as 1.4 TW, partitioned as 0.5 TW in ventilated (thermocline) waters, 0.5 TW in deep waters, and 0.4 TW in bottom waters. An additional 1 TW is estimated for power consumed in the Southern Ocean (latitudes south of 30 S), mostly associated with the enhanced mixing rate of Antarctic Bottom Water. Thus, we conclude that 2 TW is likely a lower bound for the energy consumed by mixing in the ocean interior, with roughly 3 TW of power required as the mechanical energy input.
DE: 4524 Fine structure and microstructure
DE: 4544 Internal and inertial waves
DE: 4568 Turbulence, diffusion, and mixing processes
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting