Restratification in Late Winter Lakes Induced by Cabbeling

Abstract

AbstractThe under‐ice fluid dynamics during late winter in many freshwater settings remain poorly understood. One example is how cabbeling, the generation of dense water by mixing water masses on different sides of the temperature of maximum density (Tmd), affects the vertical transport. Using high resolution numerical simulations of the development of a stratified parallel shear flow, we show that when the temperature stratification passes through Tmd, cabbeling modifies the three‐dimensional aspects of the instability with the net effect of forming an emergent, stable stratification after a brief period of strong mixing. This stratification effectively separates the quiescent upper layer from the turbulent one below, thereby limiting transport and mixing between them. We propose a simple model for the vertical fluid flux during the mixing regime, and discuss a potential mechanism responsible for the emergent stratification as well as its sensitivity to the bulk Richardson number.