A Persistent Submesoscale Frontal Slick: A Novel Marker of the Mesoscale Flow Field in a Large Lake (Lake Geneva)

Submesoscale fronts often become visible when the accumulation of biosurfactants in the water surface microlayer causes smooth surfaces, called frontal slicks, to develop. Based on in situ and remotely-sensed data, a frontal slick was documented for the first time in a lake (Lake Geneva). A quasi-stationary ∼10-km long slick formed on the warm side of a surface temperature front with strong horizontal velocity strain. The slick width increased from ∼50 to ∼200 m in ∼1.5 hr due to “feeding” by wind-driven, rapidly-moving smaller slicks. Numerical modeling results, confirmed by satellite data, indicated that the boundary between mesoscale gyres isolated warm surface water from cold water associated with wind-induced coastal upwelling. Measurements and modeling suggest that frontogenetic sharpening of the submesoscale temperature gradient created an active front with strong convergent flow. Such dynamics must be considered in buoyant material transport and the vertical exchange of surface water with deeper layers in lakes.