Fig. 1. Stratification and progressive deepening of the mixed layer during lake overturn.

Depth profiles of physicochemical parameters in Rotsee during the lake overturn period of 2016/2017. a Stratified situation in Rotsee prior to lake overturn. Oxygen in the mixed layer and methane in the hypolimnion are separated from each other. The methane-enriched hypolimnion (≥2 µM) is shaded in grey, the mixed layer is shaded in blue. b Temperature profiles of the cooling lake in autumn and winter and the resulting expansion of the mixed layer at each sampling date. In January an inverse stratification established. Blue dots indicate the mixed layer depth. c Corresponding oxygen profiles at each sampling date. Colours in b and c indicate sampling date.