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Stratification and Turnover
Stratification and Turnover
Lakes such as the Great Lakes have a tendency to stratify, or form distinct layers, in the summer months. They also layer to a certain degree in the winter months. However, in the spring and fall, the lakes experience turnover, mixing the deep and shallow waters.
Lakes such as the Great Lakes have a tendency to stratify, or form distinct layers, in the summer months. They also layer to a certain degree in the winter months. However, in the spring and fall, the lakes experience turnover, mixing the deep and shallow waters.
In the summer, deep water is insulated from the sun and stays cool, forming a bottom layer called the hypolimnion. Water near the top is warmed by the sun, forming a surface layer called the epilimnion. The epilimnion supports the majority of life in the lake; therefore, it becomes quite rich in oxygen. Late in the summer the temperature differences between the layers increase and a middle layer called the thermocline is formed.
In the summer, deep water is insulated from the sun and stays cool, forming a bottom layer called the hypolimnion. Water near the top is warmed by the sun, forming a surface layer called the epilimnion. The epilimnion supports the majority of life in the lake; therefore, it becomes quite rich in oxygen. Late in the summer the temperature differences between the layers increase and a middle layer called the thermocline is formed.
When fall comes, the epilimnion cools, making its water more dense. These waters begin to sink and mixing (turnover) begins. This turnover helps to mix oxygen-poor with oxygen-rich waters, helping the entire lake to contain healthy levels of dissolved oxygen.
When fall comes, the epilimnion cools, making its water more dense. These waters begin to sink and mixing (turnover) begins. This turnover helps to mix oxygen-poor with oxygen-rich waters, helping the entire lake to contain healthy levels of dissolved oxygen.
In the winter, the water again tends to form layers. As the temperature of the entire lake cools to near four degrees Celsius (maximum water density), turnover curtails. Surface waters, now expose to sub-zero air temperatures, may drop below freezing and form an ice cover.
In the winter, the water again tends to form layers. As the temperature of the entire lake cools to near four degrees Celsius (maximum water density), turnover curtails. Surface waters, now expose to sub-zero air temperatures, may drop below freezing and form an ice cover.
Although many times the water in a large lake remains mixed for the entire winter, another turnover may occur in spring. Warm water rises, cool water descends, and the lake readies for summer stratification once again.
Although many times the water in a large lake remains mixed for the entire winter, another turnover may occur in spring. Warm water rises, cool water descends, and the lake readies for summer stratification once again.
hypolimnion
hypolimnion
hypo = under
limne = pond or lake
ion = state of
hypolimnion = state of being under the pond or lake
The hypolimnion is the lowest layer of the lake
epilimnion
epilimnion
epi = on
limne = pond or lake
ion = state of
epilimnion = state of being on the pond or lake
The epilimnion is the top layer of the lake.
thermocline
thermocline
thermo = heat or temperature
cline = gradual change
thermocline = [layer with] gradual change in temperature
The thermocline is the middle layer of the lake. It is situated between warmer and cooler layers.
Waves
Waves
Waves transfer energy from place to place. They are mostly caused by wind.
Waves transfer energy from place to place. They are mostly caused by wind.
Currents
Currents
The Great Lakes experience currents, but they are not the same as ocean currents. This map shows their general pattern.
The Great Lakes experience currents, but they are not the same as ocean currents. This map shows their general pattern.
Image from Environment Canada
Rip currents are another movement in the Great Lakes.
Rip currents are another movement in the Great Lakes.
Flow
Flow
The Great Lakes vary in altitude (height above sea level), so they flow into one another.
The Great Lakes vary in altitude (height above sea level), so they flow into one another.
Image from the U.S. Army Corps of Engineers
Tides
Tides
The Great Lakes are located in one general location, so they do not experience tides. Only oceans experience tides.
The Great Lakes are located in one general location, so they do not experience tides. Only oceans experience tides.
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