Thermohaline intrusions lie across isopycnals

Abstract

A MAJOR task of physical oceanography is the determination of the fluxes of heat and salt and the identification of the processes responsible for producing the fluxes. For the development of realistic models of the ocean it is particularly important that fluxes across surfaces of constant density (isopycnal surfaces) be distinguished from those along isopycnals. We report here direct evidence that at least some of the 5–20-m thick intrusions commonly found in regions of strong horizontal variability (fronts) lie across isopycnals. The intrusions are formed by primarily lateral advection to produce complicated interleavings of the differing types of water across the fronts. The ubiquitous occurrence of intrusions in frontal regions and the fact that they cross isopycnal surfaces indicates that they are important factors in the vertical, as well as the horizontal, flux budgets of heat and salt. The low levels of cross-isopycnal fluxes due to small scale turbulence away from fronts¹ further suggests that these intrusions may be important in the overall global flux budgets of heat and salt.