Influence of Long-Term Climatic Changes on the Stratification of a Subtropical, Warm Monomictic Lake

Analysis of long-term records of temperature profiles in subtropical Lake Kinneret revealed changes in thermal stratification during the period 1969-1991. Thermocline depth and rate of seasonal thermocline deepening have decreased and the period of stable stratification has increased. These changes appear related to a long-term declined in mean winter air temperatures, which has produced cooler hypolimnetic waters and increased density gradients across the metalimnion. These changes in thermal structure have been accompanied by increases in hypolimnetic phosphorus concentrations and increased phytoplankton abundances in subsequent years. Although mean thermocline depth in the lake is intermediate relative to predictions based on surface area or fetch from published data on temperate and tropical lakes, winter air temperatures in the region have a salient impact on Lake Kinneret thermal dynamics in any given year.