Fig. 7: Schematic diagrams showing seasonal variations in lake thermal structures and circulation.

a The lake in late winter is characterized by weak current and uniformly distributed relatively cold water. b In early-mid summer, cold and dense subglacial discharge fills the lake deeper than the sill. Atmospheric heat is distributed to the upper layer by wind-driven circulation, resulting in the formation of a thermocline at the sill depth. c Subglacial discharge in later summer jets into the mid-layer, which drives mixing of upper warm and lowers cold waters.