Temperature variability in the nearshore benthic boundary layer of Lake Opeongo is due to wind-driven upwelling events

Abstract

A major source of temperature variation in nearshore and benthic regions of stratified lakes is due to wind-driven tilting of the thermocline. The maximum displacement of the thermocline depends upon the wind forcing, stratification, and basin morphometry; combined these three-dimensional physical parameters give the dimensionless lake number (LN). We find that the deflection of the thermocline across the length of the basin (Δh*) is correlated to the temporally averaged LN as Δh*/2h1 = 0.37LN–1, where h1 is the depth of the thermocline. We report field observations from Lake Opeongo (Ontario, Canada) showing that during large vertical movements of the thermocline, there are unstable temperature gradients in the benthic layer, as measured by the occurrence of temperature inversions on our thermistor strings. High-frequency waves interacting with the benthic boundary are most likely causing the temperature inversions. Measurements at two shallow slopes of S = 1% and 4%, show that inversions only occur when LN < 5, whereas for S = 8%, the inversions occur only when LN < 2.