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Mixing in brackish lakes due to surface ice : a physical model Bluteau, Cynthia Evelyn

Abstract

The effects of salt expelled by surface ice upon formation are investigated in the laboratory to determine whether it promotes merolnixis in lakes. The experiments consist of creating surface ice in an insulated container and letting it melt, while taking a time series of temperature measurements at different depths. The model lake has dimensions 0.34m x 0.18m x 0.3m depth and is sufficiently well insulated to allow the formation of an reverse temperature stratification in the water column. The experiments start with well-mixed saline solution at room temperature. Initial salinity ranges from 0 g L⁻¹ to 15 g L⁻¹ of potassium chloride. In all experiments, significant mixing occurred beneath the ice during its formation. The ice expels salt creating colder, more saline and hence denser water below the ice, which then mixes with warmer water located at depth. An unstable temperature stratification, supported by the accumulation of saline waters near the bottom of the lake, is present after the ice is completely melted. The proportion of salt expelled from the ice is a function of the initial lake salinity, as are the details of the circulation under the ice.

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