Aug 3, 2011 10:09 PM by John Reger

Why is the Ocean So Cold?

It's the middle of summer, the time people head to the beach in droves. But not everyone takes the plunge and gets into the water. If the ocean's too cold for you, look north for the reason: the North Pole.

"That's the transport of water that we see along our coast," said Cal Poly Oceanographer Brian Zelenke. "It's originating off the coast of Alaska."

The cold arctic air temperatures chill the surface waters which then sink as they get denser, creating a deep mass of frigid water. Then the North Pacific Gyre takes over. It's a clockwise, circular rotation of currents that carry the frigid waters from Alaska down the coast of California to the equator, where they're spun out across the Pacific.

The Coriolis Force is the next factor. Because of the earth's rotation, objects in the Northern Hemisphere, like winds and water currents, are pushed 90 degrees to the west, away from the California shoreline. That creates something called "upwelling," where deeper water is drawn up to the surface, and that deep water is cold. Zelenke explains: "When the wind blows along the coast, it pushes the water off creating something of a slope and cold water from below comes up to even that out and the up is right along our coast and that's why we're cold. That process is called upwelling."

The temperature in the ocean off the Central Coast runs between 55 and 58 degrees Fahrenheit.



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