Unseen Currents: A Blind Oceanographer Chases Undersea Storms

Sea Sights at Night:  Chris Gall

In the half-century since Swallow set sail on the Aries, oceanographers had used one of two methods to study underwater storms. Some, following Swallow’s lead, had sailed out, searched for a mesoscale eddy and, if they were lucky enough to find one, tossed a float overboard. This is called the Lagrangian method. Others had anchored data-collecting moorings in waters where eddies are known to propagate and waited for one to swirl past. This is called the Eulerian method. One day over lunch in the Woods Hole cafeteria, Amy Bower had struck on a novel way to combine the two methods. “Suppose we were to launch a float from a mooring?” she’d wondered aloud. As it happened, one of Bower’s colleagues had recently invented a device—a submerged autonomous launch platform, or SALP—that in theory, at least, could do just that.

A few days before the launch of voyage 192, I’d attended a lecture during which Bower had played an animation of the experiment that she had spent two years orchestrating. On the lecture-hall screen, the two-mile-long mooring appeared, one end anchored to the seafloor by a one-ton cylinder of solid iron, the other tugged toward but not quite to the surface by a yellow sphere, a subsurface buoy. Strung onto the half-inch-thick steel cable that linked the anchor and sphere were eight Aanderaa current meters, nine Seabird SBE 37-SM MicroCATs (devices that measure salinity and temperature), and a pair of SALPs custom-built at Woods Hole in a machine shop as large as an airplane hangar. Each of the two SALPs resembled the cylinder of a colossal six-shooter. Into their combined 12 chambers would be loaded 12 profiling floats. Once fired into the sea, these floats, noses pointed to the sky, could recalibrate their own buoyancy by filling or emptying a hydraulic bladder, and in doing so they could profile the water column at various depths.

Onto the lecture-hall screen there appeared a lethargic tornado of blue water, a cartoon Irminger Ring. The ring caught the yellow sphere and towed it along, and pressure gauges on the SALPs registered the disturbance. Another sensor registered temperature anomalies indicative of Irminger Rings, which are one to two degrees warmer than the frigid water through which they swirl. On detecting a ring, the uppermost SALP tripped a burn wire and, a moment later, spat out a single profiling float painted the bright yellow of a rubber duck.

Down the cartoon float swooped into the cartoon eddy’s watery coils. For the next several months, it would travel wherever the storm carried it, surfacing every few days to beam its findings home. If all 12 of Bower’s floats successfully launched, they would together allow her to study 12 different Irminger Rings remotely for as long as two years, even during the brutal Labrador winter, when sea spray freezes on contact to a ship’s bulwarks, shellacking them in ice. With the data her floats collected, she would be able to tell an Irminger Ring’s story from birth to death.

At 10 P.M., Sheasley instructed the helmsman to idle the engines and turn on the exterior lights, which gave the aft deck a theatrical brightness. Underneath the A-frame crane that straddled the stern, there gaped an opening in the bulwarks. Until an hour ago, a safety chain had stretched across it. Now the chain had been undone, and there was nothing between the deck and the sea; walk through the portal of the crane, step into the yawing darkness, and you’d fall into water two miles deep. Every so often, a wave came crashing up over the stern, glazing the deck with a slippery veneer that went rippling out the scuppers. This was the stage, the turbulent precipice, on which the night’s action would play out.