The Production and Dissipation of Compensated Thermohaline Variance by Mesoscale Stirring
Author(s)
Smith, K. Shafer; Ferrari, Raffaele
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Temperature–salinity profiles from the region studied in the North Atlantic Tracer Release Experiment (NATRE) show large isopycnal excursions at depths just below the thermocline. It is proposed here that these thermohaline filaments result from the mesoscale stirring of large-scale temperature and salinity gradients by geostrophic turbulence, resulting in a direct cascade of thermohaline variance to small scales. This hypothesis is investigated as follows: Measurements from NATRE are used to generate mean temperature, salinity, and shear profiles. The mean stratification and shear are used as the background state in a high-resolution horizontally homogeneous quasigeostrophic model. The mean state is baroclinically unstable, and the model produces a vigorous eddy field. Temperature and salinity are stirred laterally in each density layer by the geostrophic velocity and vertical advection is by the ageostrophic velocity. The simulated temperature–salinity diagram exhibits fluctuations at depths just below the thermocline of similar magnitude to those found in the NATRE data. It is shown that vertical diffusion is sufficient to absorb the laterally driven cascade of tracer variance through an amplification of filamentary slopes by small-scale shear. These results suggest that there is a strong coupling between vertical mixing and horizontal stirring in the ocean at scales below the deformation radius.
Date issued
2009-10Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary SciencesJournal
Journal of Physical Oceanography
Publisher
American Meteorological Society
Citation
Smith, K. Shafer, and Raffaele Ferrari. “The Production and Dissipation of Compensated Thermohaline Variance by Mesoscale Stirring.” Journal of Physical Oceanography 39.10 (2009): 2477-2501. © 2009 American Meteorological Society
Version: Final published version
ISSN
0022-3670
1520-0485