The joint effects of riverine, thermal, and wind forcing on a temperate fjord lake: Quesnel Lake, Canada

Abstract

Field data obtained in 2003–2004 are used to describe the influence of atmospheric and riverine forcing on the thermal history of fjord-type lakes using Quesnel Lake, British Columbia, Canada as an example. Typical of fjord-type lakes, Quesnel Lake is narrow, long (>100km total thalweg), multi-armed (three arms of comparable size), deep (maximum depth>500m), and has multiple basins separated by sills. The lake's annual thermal history responds to the joint forcing of surface heat exchange, river inputs, and wind stress. The lake's annual heat budget is dominated by surface radiative fluxes, and riverine input of heat is insignificant in this medium residence time lake (10years). Despite being insignificant to the annual heat budget, the three major rivers that feed the three arms of the lake contribute to the overall lake circulation pattern. Since these rivers have differing salinities, it is possible to identify, using temperature/salinity correlation diagrams, patterns of riverine circulation interflowing in the lake. Data from a 1-year thermistor-chain record suggests exchange between surface and intermediate waters occurs twice annually, but deep-waters below 150–250m are mainly renewed during autumn, by strong and episodic atmospheric forcing. This is because wind-forced turbulent diffusion and gravitational convection triggered by wind forced displacement of isotherms (initiating thermobaric instability) are required for full overturn and deep-water renewal.