Complex interactions between meteorological parameters and the thermal regime of two tropical, high altitude crater lakes (Nevado de Toluca, Mexico).

Using long-term time series of meteorological and water-column parameters, the dynamics of two lakes separated by about 500 m from each other by a central lava dome, located at 4207 m above sea level in the volcano crater of Nevado de Toluca, Mexico were explored. Because of the strong wind-forcing previously measured on the volcano slope and the proximity of the lakes, wind-mixing was expected, with similar dynamics in both lakes. However, the meteorological parameters in the crater were significantly different than on the slope of the volcano, due to the dome and the high walls of the crater, which weakened wind speeds, modified wind direction, and reduced exposure to solar radiation by almost 20% in the crater compared to on the volcano slope. The rate and depth of thermal penetration into each lake differed by an order of magnitude, related with differential insolation due to crater wall shading, along with differences in transparency, most likely due to differential algal growth and suspended matter. At times, rapid surface cooling occurred during periods of reduced insolation and calm winds, leading to strong vertical convection and the formation of a characteristic step profile in the water column rather than the predicted wind mixing. These results are important for interdisciplinary studies of these and other alpine lakes and, in particular for biophysical coupling in these unique hydrological systems.