Tuesday, October 02, 2007

Daddy, why is the sea salty?

Finally, I have a reasonably convincing answer to something that has bugged me for years (and had it printed at that!):
THE QUESTION: Landlubber Luke Mastin of Toronto wanted to know why the seas and oceans are salty (and very salty at that) but other large bodies of water, including the Great Lakes, are not.
THE ANSWER: Lakes are fed by rivers, which in turn are fed by rainwater. As rainwater passes through soil and around rocks, it dissolves some minerals, including salt, but contains these minerals in very low concentrations. However, while lakes are fed by rivers, they are also drained by them.
"The Great Lakes are not (noticeably) salty because water flows into them as well as out of them, carrying away the low concentrations of minerals in the water," writes Michael Moore of Toronto.
Eventually, this water, with its small load of dissolved minerals or salts, reaches the sea. "The oceans are therefore salty because water flows into them but leaves only by evaporation, leaving the minerals behind to get ever more concentrated," writes Mr. Moore.
Adds John Yandon of Ottawa: "If a lake has no outflow, it will become as salty, or more so, than the oceans. Some notable examples of salty lakes are the Great Salt Lake in Utah, the Salton Sea in California and the Dead Sea in Jordan."
And who says it doesn't pay to write into the papers?

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