Double-Diffusive Layering in the Canada Basin: An Explanation of Along-Layer Temperature and Salinity Gradients

Abstract

Double-diffusive mixing gives rise to layered structures in the Arctic Ocean: layers within a double-diffusive staircase overlying deeper layers associated with thermohaline intrusions. These layers exhibit well-defined lateral temperature and salinity gradients. Gradients in salinity along individual layers change sign with depth, while along-layer gradients in temperature remain the same sign with depth. A theoretical formalism is put forward to explain these features in terms of vertical divergences of double-diffusive fluxes; temperature and salinity gradients along layers are set by the depth-dependent ratio of double-diffusive heat to salt fluxes. Examination of fine structure in temperature and salinity profiles reveals how the net flux ratio depends upon whether the layer is part of an evolving thermohaline intrusion or a staircase. The physical framework in context with observations of varying along-layer gradients in temperature and salinity provides evidence for thermohaline intrusions evolving to a staircase and describes the parameters that dictate this process. Results bring new understanding to heat and salt transport in the Arctic Ocean as well as the physics of double-diffusive layering in the world's oceans.