Author(s): A. L. Forrest; B. E. Laval; R. Pieters
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Keywords: No Keywords
Abstract: Radiative penetrative convection was investigated under-ice in Pavilion Lake, a midsize temperate lake (5 km2) in the interior of British Columbia, during the initial onset of spring thaw in February 2008. This convection was observed using a conductivitytemperature-depth (CTD) sensor, mounted on an autonomous underwater vehicle (AUV) that was flown repeatedly along horizontal transects (～ 450 m in length) at selected depths during a 1–5 hour time period. Four distinct thermal layers were observed beneath the ice (～50 cm thick): a stratified diffusive layer just beneath the ice; a well-mixed convective layer; an entrainment layer; and, a weakly stratified quiescent layer (to bottom). The collected horizontal temperature data revealed a wide, central region of the basin displaying evidence of penetrative convection, surrounded by regions with negligible heat changes, which was self-consistent at multiple depths. In addition to the AUV transects, vertical temperature measurements were collected with both a CTD profiler and a thermistor chain at one location during each of the AUV missions allowing the thermal structure to be realized in three dimensions. Concurrent measurements taken from moored in situ temperature and conductivity sensors demonstrate a distinct salinity stratified layer (～10 m thick) developing in the benthic region during this time period likely due to groundwater inflow. These records also demonstrate temperature fluctuations that are proposed to result from density driven currents generated as a result of radiative convection in the upper layer. Resolving the dominant forcing driving this evidence of physical transport across the benthic region would provide insight into previously unresolved physical dynamics of temperate lakes.
Year: 2009