A subsurface look at the upwelling phenonmenon

The animation below shows vertical displacement of ocean water in a vertical cross-shore section near Lincoln City during 45 days of an upwelling season (using model results from the end of May to the beginning of July 2001). Different colors show water of different temperature. Cold water (blue) is heavier than warm water, so it lays closer to the ocean bottom. Most times deep ocean water is also saltier than surface water. As a result of upwelling (southward winds), deep ocean water is moved along the bottom closer to the coast and surface. During periods of weak winds or northward winds this cold water returns back to deeper levels. The lower plot in the movie shows the direction and the strength of the wind forcing, measured as “wind stress.” It is more often directed to the south, although there are periods of wind reversal. A sliding vertical red line shows the time of the image.

Question 1: On a summer day on an Oregon beach, why is it too cold to swim? See answer below.

Answer to Question 1: The nearshore water is brought from the depth, where it was not exposed to the sun.

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