Unseen Currents: A Blind Oceanographer Chases Undersea Storms

"Tie That Down!":  Chris Gall

In the last chapter of The Sea Around Us, published in 1950, Rachel Carson writes that the benighted cartographers of the Middle Ages had thought of the ocean as the “dread Sea of Darkness.” Over the centuries, little by little, explorers and then scientists had pulled the veil of darkness back. “Here and there, in a few out-of-the-way places, the darkness of antiquity still lingers over the surface of the waters,” Carson writes. “But it is rapidly being dispelled, and most of the length and breadth of the ocean is known; it is only in thinking of its third dimension that we can still apply the concept of the Sea of Darkness. It took centuries to chart the surface of the sea; our progress in delineating the unseen world beneath it seems by comparison phenomenally rapid.” Carson didn’t end her story on a triumphant note. Prophetically, she added this: “Even with all our modern instruments for probing and sampling the deep ocean, no one now can say that we shall ever resolve the last, the ultimate mysteries of the sea.” Which brings us to mesoscale eddies.

In 1959, aboard a ketch called the Aries, an English oceanographer named John Swallow sailed northeast out of Bermuda into the Sargasso Sea in search of a vast, deep and altogether hypothetical northerly current. Into the water he lowered neutrally buoyant floats soldered together from aluminum scrap. Then he lowered his hydrophone and listened for pings. His floats sauntered extravagantly, first one way, then another. They spun. They described arcs. They meandered. They doubled back. Not one of them drifted steadily north, as Swallow had expected. His floats hadn’t charted rivers in the sea. Instead they had revealed watery breezes, watery winds, watery storms, and this revelation fundamentally changed the way scientists think of the ocean.

There are still oceanographers preoccupied by the ocean’s third dimension, but a growing number—perhaps even most—are thinking about its fourth and darkest dimension: time. Just as geographers and cartographers mapped the earth, so the physical oceanographers of the 19th century set out to map the sea—to chart its currents and fathom its depths. As Swallow’s discovery made clear, the geographic analogy turned out to be a poor one. What the ocean resembled most was the skies. Indeed, the “ocean-atmosphere interface” is far more permeable than it looks. The climate of the planet stretches all the way, oceanographers tell us, from the depths of the Mariana Trench to the outer edge of the stratosphere.