The idea that our oceans are dangerous and unpredictable runs from The Odyssey to The Perfect Storm to Seinfeld. But in another sense, the ocean is remarkably stable and rhythmic. Ship logs have been used to calculate ocean currents for centuries. Benjamin Franklin’s 1770 map of the Gulf Stream—a fast-moving surface current that runs north along the Atlantic coast of the United States—was a godsend for trade ships. Today, modern sensing technology has mapped out currents in fine detail, helping to calculate weather patterns and pollution pathways.

These maps have revealed an ocean in constant motion. There are huge circling gyres, surface currents that run up and down coasts and around whole continents, and small whirlpools and eddies.

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