Conductivity of a cyclonic eddy in an ice-covered lake

Investigation of the horizontal and vertical variability of temperature and conductivity beneath the ice cover of a midsize (5 km2) temperate lake has shown the existence of a submerged cyclonic eddy. Eddies potentially play a role in under-ice mixing dynamics that have previously not been studied. Measurements of this feature were made with a Conductivity-Temperature- Depth (CTD) sensor mounted on an autonomous underwater vehicle (AUV) deployed through the ice-cover. This eddy was relatively stable in size, location and density structure throughout the 6-day observation period. The density gradients calculated from the measured temperature and conductivity field are in cyclogeostrophic balance. These observations support the growing body of work emphasizing the importance of Coriolis forces in smaller ice-covered lakes. In this paper we focus on the conductivity, which varied across the eddy and provide a closer examination of the salt excluded from the ice and the background conductivity in the surrounding waters. These conductivity data hint that salt exclusion may have played a role in forming the eddy.