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Matt:

I just got back from a visit to Miami. When I was swimming in the Atlantic Ocean I could swear that the water there was saltier than it is off San Diego's Coast. True or false?

-- P.K., Talmadge

As a swimmer you sample only the tiniest fraction of the smallest bit of on-shore ocean water, which can be influenced by runoff, rivers, or other land-based water sources. A swimmer is hardly the best judge of a ocean's salinity. I think you're hallucinating, but according to our friends at Scripps Institution, you're also right. Average surface salinity of the Atlantic is from 36 to 36.5 parts per thousand of salts (many different kinds, not just sodium chloride). The Pacific's is 33 to 33.5. A miniscule difference, lending further credence to my hallucination theory.

If you look at Earth's water cover as essentially a big, odd-shaped swimming pool, it's hard to figure why one part would be saltier than another. For the savory Atlantic, we can thank the Mediterranean Sea. The nearly landlocked Med acts as a huge evaporation pool and flushes very salty water back into the Atlantic. The Pacific has no comparable body of water to raise it's salt level, though the Gulf of California is slightly more saline than the Pacific. One other salty spot on the globe is the Indian Ocean, which receives outflow from the Red Sea and the Persian Gulf, both evaporation bodies.

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