Mixing Dynamics in Lakes Across Climatic Zones

Abstract

Interactions between climatic and geographic conditions lead to variations in mixing dynamics in lakes. Based on these factors and depth, lakes historically have been classified with respect to the timing and frequency of full water column mixing. In this chapter, we compare the relative role of wind forcing versus heat loss in mixing and deepening the upper mixed layer as a function of latitude. Similarly, we compare mixing dynamics in the stratified part of the water column. Due to greater evaporative heat losses in tropical lakes, mixed layer deepening can be more rapid and to deeper depths than in temperate lakes. In temperate and arctic lakes, wind and heat loss often make similar contributions towards mixing. As water temperatures decrease, the relative contribution from wind increases. During the stratified period, vertical exchange between the upper and lower water column is mediated by instabilities in the internal wave field. Such instabilities may occur on a diurnal basis in stratified tropical lakes. They occur in many small arctic lakes during the passage of fronts, so recycled nutrients can be supplied to the upper water column intermittently. They are less frequent in small temperate lakes due to the stronger stratification, and vertical exchanges may need to be mediated by biological processes. How frequently they occur in larger lakes depends upon the frequency of frontal systems with high winds.