Contrasting the interleaving in two baroclinic ocean fronts

Abstract

To investigate the effects of baroclinicity on frontal interleaving, we contrast the interleaving characteristics of two fronts, one in the Arctic Ocean and the other surrounding a Mediterranean salt lens (Meddy). The Meddy is broken into two parts based on the vertical temperature and salinity structure, so our comparison involves three sets of interleaving observations. The cross-front slopes of intrusions relative to horizontal and isopycnal surfaces are taken to be key diagnostics of the interleaving dynamics. Assuming the observed slopes match those that were present during the initial growth of interleaving, we use an instability theory to infer the dominant form of double diffusion that was active during the growth stage. Then, to investigate the observed interleaving, we use a steady-state model to infer the dominant form of double diffusion at the time of observation. In the Arctic Ocean front, it appears that different forms of double diffusion dominated the two stages of interleaving (salt fingering during the growth stage and diffusive convection at steady state). In contrast, in the Meddy, the same form of double diffusion appears to have dominated both stages of interleaving (salt fingering in the lower part of the Meddy, diffusive convection in the upper part). In the Arctic Ocean front, the observations suggest that interleaving was driven by baroclinicity as well as double diffusion. In both parts of the Meddy, however, driving was by double diffusion only. Motivated by these differences, we suggest a new intrusion classification scheme, based on the slopes of intrusions relative to horizontal and isopycnal surfaces.