Oceanology: Underwater Waves Make Underwater Weather

After years of patient probing, oceanographers still have only the sketchiest notions about the shape of the drowned, undersea landscape that makes up 70% of the earth’s crust. They know even less about undersea “weather”—the currents, eddies and swift temperature changes that sweep across the ocean bottom like winds and storms on land. Not until Columbia University’s Hudson Laboratories announced the first direct measurements of deep waves, could oceanographers be sure that the great, lazy surges actually exist.

The latest contribution to submarine meteorology was made by modified Swallow buoys,* which are 13-inch aluminum spheres ballasted to sink until they reach water of a selected density. Crammed with apparatus that reports its observations with sonic pings, the buoys can be followed accurately through the depths. They can communicate with each other and measure their distance apart; they can be instructed by a coded sonic signal and told when to drop ballast, rise to the surface, and call by radio for pickup.

Slow Surge. When Columbia’s Dr. Theodore Pochapsky tossed his first buoys into the Caribbean, his calculations told him that they would move evenly with the deep-down currents, but to his surprise they were tossed by unseen waves. “Instead of remaining at a constant level,” he says, “they bobbed incessantly in regular up-and-down swings of about ten feet.” As the oceanographers looked farther, they also found submarine surges deep in the Atlantic east of Bermuda and as far south as the equator. All of them moved only fractions of a mile per hour.

The deep-down waves are vertical fluctuations similar to surface waves, but instead of rolling across the sharp interface between wind and water, they travel in transitional zones between water layers of different density. No one knows what causes them. It may be the turbulence of bottom currents flow ing over ridges and valleys of the sea bed; there may be a connection with the rotation of the earth. Some of Dr. Pochapsky’s buoys rose and fell 100 ft. twice a day, although the surface far above them moved very little with the tides.

High Hopes. Fascinated by the submarine waves, which must surely be important to marine life as well as to man’s undersea warfare, Columbia’s researchers are now pursuing them with more observant buoys that report temperature and pressure as well as movement. “It will be interesting to see what sort of underwater breakers form when internal waves 100 ft. high hit the continental shelf 50 miles away from our Eastern coast,” says Dr. Pochapsky. He has high hopes that such studies will mark a significant advance in the infant science of submarine meteorology, which may some day learn to forecast the changes of underwater weather, and may someday use such knowledge to help forecast weather above the surface.

*Originally invented by British Oceanographer John C. Swallow.