The production of temperature and salinity variance and covariance : implications for mixing
The production of temperature and salinity variance and covariance : implications for mixing
Date
2013-02
Authors
Schanze, Julian J.
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DOI
10.1575/1912/5741
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Keywords
Oceanic mixing
Ocean circulation
Ocean circulation
Abstract
Large-scale thermal forcing and freshwater fluxes play an essential role in setting
temperature and salinity in the ocean. A number of recent estimates of the global
oceanic freshwater balance as well as the global oceanic surface net heat flux are used
to investigate the effects of heat- and freshwater forcing at the ocean surface. Such
forcing induces changes in both density and density-compensated temperature and
salinity changes (’spice’). The ratio of the relative contributions of haline and thermal
forcing in the mixed layer is maintained by large-scale surface fluxes, leading to
important consequences for mixing in the ocean interior. In a stratified ocean, mixing
processes can be either along lines of constant density (isopycnal) or across those
lines (diapycnal). The contribution of these processes to the total mixing rate in the
ocean can be estimated from the large-scale forcing by evaluating the production of
thermal variance, salinity variance and temperature-salinity covariance. Here, I use
new estimates of surface fluxes to evaluate these terms and combine them to generate
estimates of the production of density and spice variance under the assumption of
a linear equation of state. As a consequence, it is possible to estimate the relative
importance of isopycnal and diapycnal mixing in the ocean. While isopycnal and diapycnal
processes occur on very different length scales, I find that the surface-driven
production of density and spice variance requires an approximate equipartition between
isopycnal and diapycnal mixing in the ocean interior. In addition, consideration
of the full nonlinear equation of state reveals that surface fluxes require an apparent
buoyancy gain (expansion) of the ocean, which allows an estimate of the amount of
contraction on mixing due to cabbeling in the ocean interior.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2013
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Citation
Schanze, J. J. (2013). The production of temperature and salinity variance and covariance : implications for mixing [Doctoral thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution]. Woods Hole Open Access Server. https://doi.org/10.1575/1912/5741