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Current global records have shown an increase in temperature over the last decade. There's been an increase in rainfall and large changes in regional distribution. The temperature of the Great Lakes increases in the summer. The lakes are taking in the extra solar energy from the atmosphere, it acts as a heat sink throughout the summer. Warm water holds less oxygen than cold water, and when combined with high respiration rates, the summer lakes lose most of their oxygen. The decrease in the warmer water temperatures leads to an increase in the death of fish. We can see a more dramatic decrease when large amount of algae are found in one area.
As the lakes absorb light energy it is converted to heat energy; warming the surface of the water. Throughout the summer, thermally stratified lakes are warmer on top and cooler at the bottom. The warm surface is called the epilimnion, and the cooler bottom layer the hypolimnion. The zone between the warm and cold is called the thermocline. The epilimnion and the hypolimnion need to mix but the thermocline acts as a barrier. In order for the two layers to mix properly energy is needed. The lakes get the energy from wind. In the late summer and early fall, the epilimnion begins to decrease in temperature. The thermocline starts to fade and the two layers mix thoroughly. The lake “turns over” from top to bottom. This process is known as fall overturn.
