Ocean Movements
Six ships checking the Gulf Stream’s course through the Atlantic Ocean over a 2-week period found the variations shown above.
The infrared film photograph shows the edge of the Gulf Stream. The visible line between the Gulf Stream, which is on the right, and Labrador water is made by Sargassum weed concentrated at the interface.
The ocean is constantly in motion—not just in the waves and tides that characterize its surface but in great currents that swirl between continents, moving (among other things) great quantities of heat from one part of the world to another. Beneath these surface currents are others, deeply hidden, that flow as often as not in an entirely different direction from the surface course.
These enormous “rivers”—quite unconstant, sometimes shifting, often branching and eddying in a manner that defies explanation and prediction—occasionally create disastrous results. One example is El Niño, the periodic catastrophe that plagues the west coast of South America. This coast normally is caressed by the cold, rich Humboldt Current. Usually the Humboldt hugs the shore and extends 200 to 300 miles out to sea. It is rich in life. It fosters the largest commercial fishery in the world and is the home of one of the mightiest game fish on record, the black marlin. The droppings of marine birds that feed from its waters are responsible for the fertilizer (guano) exports that undergird the Chilean, Peruvian, and Ecuadorian economies.
Every few years, however, the Humboldt disappears. It moves out from shore or simply sinks, and a flow of warm, exhausted surface water known as El Niño takes its place. Simultaneously, torrential rains assault the coast. Fishes and birds die by the millions. Commercial fisheries are closed. The beaches reek with death. El Niño is a stark demonstration of man’s dependence on the sea and why he must learn more about it.
There are other motions in the restless sea. The water masses are constantly “turning over” in a cycle that may take hundreds of years, yet is essential to bring oxygen down to the creatures of the deeps, and nutrients (fertilizers) up from the sea floor to the surface. Here the floating phytoplankton (the plants of the sea) build through photosynthesis the organic material that will start the nutrient cycle all over again. Enormous tonnages of these tiny sea plants, rather than being rooted in the soil, are separated from solid earth by up to several vertical miles of saltwater. Sometimes, too, there is a more rapid surge of deep water to the surface, a process known as upwelling.
Internal waves, far below the surface, develop between water masses that have different densities and between which there is relative motion. These waves are much like the wind-driven waves on the surface, though much bigger: Internal waves may have heights of 300 feet or more and be 6 miles or more in length!
A dividing cell of the diatom Corethron hystrix. Diatoms, one-celled photosynthetic plants, are the primary producers of organic matter in fresh waters.
Ocean currents feed sand from nearby beaches into this “sandfall”, which is about 30 feet high, in a submarine canyon off Baja California.
Among other motions of the sea there are landslides, or turbidity currents, which are great boiling mixes of mud, rock, sand, and water rushing down submarine mountainsides at speeds of a mile a minute. They destroy everything in their paths and spread clouds of debris over the abyssal plains like a sandstorm, producing fanlike deposits radiating far out from the base of the slope. And there are tsunamis, or seismic sea waves—popularly misnamed “tidal waves”—that transmit energy from undersea earthquakes or volcanic eruptions. At sea, these waves are only a few inches high, but they may travel great distances at 500 miles an hour. As they approach the shoaling waters of a coast, they are slowed to about 30 miles an hour and build up great surface waves capable of destroying harbor and coastal installations.