Fine-Scale hydrodynamic modelling of Lake Ontario: Has climate change affected circulation patterns?

Abstract

Abstract The circulation in Lake Ontario is well known from past field and modelling studies. However, apparent changes in wind pattern, possibly due to climate change, have resulted in subtle changes in the currents’ formation that have implications for water resources and aquatic habitat. A high resolution three-dimensional numerical model using the Danish Hydraulic Institute’s (DHI) MIKE 3 modelling framework based on a flexible mesh, was developed to describe lake-wide and coastal circulation features in 2018, which were then contrasted with past studies. The validated model effectively described lake-wide processes that include season-specific large gyres in the Rochester and in the Mississauga basins, and coastal currents along both northern and southern shorelines. During the isothermal season (non-stratified), a well-defined westward flow in the middle of the lake separates an anticyclonic (clockwise) gyre in the north, from the gyre and westward currents in the south. During the stratified season, key physical processes depicted in the model in the offshore and nearshore waters including, near-inertial waves (~ 17 h), upwelling events frequency (5–10 days) and surface seiches (~ 5 h) generally correspond with past studies. Upwelling events are the predominant northern nearshore physical processes and are occurring during periods of south-westerly winds. Episodic Kelvin waves are mostly limited to the northern shore where wind direction and morphology can sustain them and where cross-shore transport at the coastal boundary layer is minimal. The results, backed by field observations, suggest that predominant circulation patterns in the northern nearshore have changed in recent years during the stratified season.