Diapycnal Advection by Double Diffusion and Turbulence in the Ocean

The role of double-diffusive mixing in the North Atlantic thermocline is considered. Mixing observations are analyzed in terms of the stability parameters for shear and double-diffusive convection, and a nondimensional ratio of dissipation rates. While the model for turbulence describes most dissipa...

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Bibliographic Details
Main Author: Laurent, Louis St.
Other Authors: MASSACHUSETTS INST OF TECH CAMBRIDGE
Format: Text
Language:English
Published: 1999
Subjects:
Physical and Dynamic Oceanography
*MIXING
*MIXED LAYER(MARINE)
*SALINITY
THESES
TURBULENCE
BATHYMETRY
DIFFUSION
NORTH ATLANTIC OCEAN
ABYSSAL ZONES
ADVECTION
THERMOCLINES
*DIAPYCNAL MIXING
SALT FINGER MODELS
Antarctic
Antarc*
North Atlantic
Online Access:http://www.dtic.mil/docs/citations/ADA376654
http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA376654
Description
Summary:The role of double-diffusive mixing in the North Atlantic thermocline is considered. Mixing observations are analyzed in terms of the stability parameters for shear and double-diffusive convection, and a nondimensional ratio of dissipation rates. While the model for turbulence describes most dissipation occurring in high shear, dissipation in low shear is better described by the salt-finger model, and a method for estimating the salt-finger enhancement of the diapycnal haline diffusivity over the thermal diffusivity is proposed. These calculations suggest that salt-finger driven haline flux drives diapycnal downwelling in the upper thermocline. The role of turbulence occurring above rough bathymetry in the abyssal Brazil Basin is also considered. The mixing levels along sloping bathymetry exceed the levels observed on ridge crests and canyon floors. Additionally, mixing levels modulated in phase with the spring-neap tidal cycle. A model of the dissipation rate is derived and used to specify the turbulent mixing rate and constrain the diapycnal advection in an inverse model for the steady circulation. The inverse model solution reveals the presence of a secondary circulation with zonal character. These results suggest that mixing in abyssal canyons plays an important role in the mass budget of Antarctic Bottom Water. Sponsored in part by Grant NSF-OCE94-15589. Prepared in cooperation with Woods Hole Oceanographic Institution, Woods Hole, MA.

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