Metalimnetic Oxygen Minima in Lake Ontario, 1972

Abstract

Dissolved oxygen profiles taken in Lake Ontario in 1972 indicate the presence of a distinct and persistent metalimnetic oxygen minimum during the stratified season. Evidence indicates the phenomenon occurred in previous years as well. The depth and magnitude of the minimum were closely related to the thermocline depth and strength of stratification. Lowest minimum values in 1972 occurred in early to mid September and were 8.6 mg/l dissolved oxygen and 82% saturation. Offshore the minimum decreased from west to east across the lake and was lesser in magnitude nearshore and in the northeast. During the nonstratified period oxygen concentrations remained relatively constant with depth at approximately saturated values.