NASA / SCIENCE PHOTO LIBRARY NASA / SCIENCE PHOTO LIBRARY
Global ocean circulation. Ocean currents flow around the world due to differences in temperature and salinity. A current of warm water from the Pacific Ocean travels westward on the ocean surface. As it flows, it evaporates and becomes saltier. The Gulf Stream carries the warm, salty water up along the East Coast of the United States, then towards Europe. At colder northern latitudes, the water becomes so dense that it sinks to the sea floor and travels south.
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