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Upwelling

Upwelling. Demo vid: http://www.youtube.com/watch?v=XV90dy0ns1U&NR=1 Open ocean circulation- upwelling: http://www.youtube.com/watch?v=SHTDzLlUU6M Take notes over the clip. Lake Turnover. Demo. http :// www.youtube.com/watch?v=uSFSNTI67wc. Dimictic Lakes – Annual Cycle.

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Upwelling

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  1. Upwelling • Demo vid: http://www.youtube.com/watch?v=XV90dy0ns1U&NR=1 • Open ocean circulation- upwelling: http://www.youtube.com/watch?v=SHTDzLlUU6M • Take notes over the clip

  2. Lake Turnover

  3. Demo • http://www.youtube.com/watch?v=uSFSNTI67wc

  4. Dimictic Lakes – Annual Cycle Seasonal heating and cooling Wind creating turbulence

  5. Freshwater Lake Turnover • The layering of lakes has to do with the relationship between water density and temperature. • Water is most dense at 39 Fahrenheit (4 degrees Celsius) • As water warms or cools from that mark it gets less dense.

  6. Winter • In the winter, most of the water under the ice is 39⁰ Fahrenheit (ice is at least 32⁰); • However, there is a thin layer of water under the ice that is colder than 39 and therefore less dense. • This thin layer of water floats on top of the lake under the ice throughout the winter.

  7. Colder, Less Dense Water

  8. Spring • In the spring, ice melts off the lake, and the top layer of water on the lake gets warmed by the sun to 39 F, which matches the temperature of the rest of the lake water. • Then the spring wind picks up and the lake mixes again. This is called spring turnover. • Oxygen and nutrients get distributed throughout the water column as the water mixes

  9. Summer • Over the summer months, the surface waters begin to be heated by the sun again. As the surface temperature rises, water on the lakes surface becomes less dense and a thermocline forms • Three layers are formed: • Epilimnion(“epi” meaning top, as in epidermic needle) • Thermocline • Hypolimnion

  10. Fall • In the fall, the sunlight is not as strong and the nights become cooler. This change in season allows the top layer of the lake to cool off. • As the water cools, the density difference between the top layer of the lake and bottom layer is not as great. Wind can then mix the layers. Eventually the top layer fades and mixes with the middle layer.

  11. FaLL • The thermocline sinks in the water column as the heavier upper water layer forces it deeper. Soon, though, the temperature in this mixed upper layer equals that of the bottom layer; wind easily mixes the entire water column because similar temperature and density exist throughout. • This mixing allows oxygen and nutrients to be distributed across the whole water column again, and is called fall turnover

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