Life and demise of intrathermocline mesoscale vortices

Abstract

This study is focused on finescale dissipation mechanisms of intrathermocline mesoscale vortices exemplified by meddies, large anticyclonic salt lenses of Mediterranean origin commonly observed in the lower North Atlantic thermocline. High-resolution numerical experiments are diagnosed to quantify the rates of temperature and salinity (T, S) dispersion in salt lenses and to determine the relative contribution of various mixing processes in the decay of their thermohaline signatures. This study finds, in agreement with observations, that meddies dissipate on the characteristic time scale of several years and that their ultimate disintegration can be attributed to thermohaline interleaving driven by double-diffusive mixing. Mechanically generated turbulence, on the other hand, tends to suppress the interleaving and therefore has an adverse net effect on eddy dispersion. It is found that the dispersion properties of static lenses, characterized by density-compensated T-S patterns, and their rapidly rotating counterparts are dramatically different.