key words: physical limnology, stratification, deep water, meromixis, thermobaric effect running header: very deep, thermally stratified lakes for submission to Geophysical Research Letters -2 -
AbstractIn very deep freshwater lakes, deep recirculation presents itself with remarkable differences to shallower lakes. We consider the stratification where density gradients are exclusively due to temperature differences. The annual circulation patterns are discussed for various climatic 5 conditions. Very deep lakes do not necessarily produce full overturns during T md transition in autumn and spring. Peculiarities of the stratification are derived for cases, in which surface temperatures cross 4°C during the annual cycle: Firstly, the asymmetry between autumn and spring circulation, secondly, the proximity of temperature to the T md profile, and thirdly, the isothermal deep water. We compare conceptual model results of horizontally homogeneous 10 lakes with measurements in very deep caldera lakes in Japan (Lakes Ikeda, Tazawa, Toya, Kuttara and Shikotsu). Between oligomictic lakes and thermobarically stratified lakes, we have found lakes circulating reliably despite their enormous depth. We discuss susceptibility to climate variability supported by comparisons with single point measurements from the 1920s and 1930s.