Growth and steady state stages of thermohaline intrusions in the Arctic Ocean

Abstract

Thermohaline intrusions are a widespread feature of the Arctic Ocean pycnocline and may be important for the lateral transport of heat, salt, and other tracers. In an attempt to understand the dynamics of the intrusions, we present an analysis of hydrographic observations of a front north of Svalbard. Following intrusions from profile to profile, we find that they slope upward toward the cold, fresh side of the front. However, their slope is less than that of the background isopycnals, so that the intrusions slope between horizontal and isopycnal surfaces in the “wedge” of baroclinic instability. Our analysis proceeds in two stages. First, to determine what might have caused the initial growth of the intrusions, we compare the observed intrusion properties with predictions of an instability theory. The results suggest that the intrusions developed as a form of double‐diffusive interleaving, with fluxes dominated by salt fingering and additional forcing by baroclinicity. Second, to investigate the observed finite amplitude interleaving, we apply a steady state model to the observations. A key result is that diffusive convection, not salt fingering, must be the dominant form of double diffusion in order to reach steady state. This fundamental change in dynamics is discussed in the context of adjustment from the growth stage to an eventual steady state.