Virtually everybody knows that the world’s oceans have currents. But few know who first discovered them, why they are important, or what can be gained by mapping them in greater detail. NASA’s Aquarius satellite is collecting related data from the world’s oceans, and a recent NASA video highlighted the vital importance of its currents.

Life on earth depends on the continuous movement of ocean water to mix nutrients both horizontally and vertically, otherwise ocean life—and, by extension, life elsewhere on earth—would not survive. The vast majority of the planet’s breathable oxygen is generated by marine algae, which are fueled by this mixing.

Ocean currents have complicated causes. The video, while highlighting NASA’s Aquarius satellite project, also explained that “at the ocean surface, currents are primarily driven by winds. Deep below the surface, however, currents are controlled by water density, which depends on the temperature and salinity of the water.”1 Aquarius detects sea surface salinity data from the world’s oceans—and not just from shipping lanes, from which most data have historically been obtained.2

Water becomes denser and saltier as it cools, and as a result it sinks below less dense waters. The NASA video stated, “This globally interconnected process of overturning circulation occurs in all ocean basins and helps to regulate earth’s climate.”1

Thus, ocean currents feed vital organisms and help govern climate, including the distribution of vital rain. But these things were known in the 1800s. Matthew Maury, the father of modern oceanography, was the first to establish the causes and courses of marine currents. He rejected contemporary but lesser theories of what causes currents, including the idea that they are forced by river runoff. In 1855, Maury wrote, “Hence we say we know that the sea has its system of circulation, for it transports materials for the coral rock from one part of the world to another.”….3

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