“In all my experience, I have never been in any accident . . . or any sort worth speaking about.”
—E.J. Smith, captain, RMS Titanic
Not only are the oceans capable of sinking large ocean liners, but they also team up with the atmosphere to create long-standing climate conditions all over the globe. This power makes them the biggest influence of all on the earth’s weather and climate.
Knowing that giant rivers of air meander through the atmosphere, it probably wouldn’t surprise you to find that the oceans have their own streams and eddies as well. Prevailing winds get surface waters moving along with them, and the effect transfers down through the ocean layers, creating currents that span entire seas. Even deeper currents are caused by the water’s density. The sea is denser at greater depths because cold water is heavier than warmer water; the molecules in frigid water have been squeezed closer together. Seawater also contains salt, which makes it heavier than fresh water.
In the 1500s, Juan Ponce de León, who had arrived in the New World on Columbus’s second voyage, discovered that his ship was unable to make headway while sailing south from Saint Augustine in what is now Florida, even though the wind was behind him. Unaware of it at the time the explorer was trying to sail against the Gulf Stream, part of a vast river of water that circles the entire Atlantic Ocean. Later, conquistadors learned to take advantage of this current by riding it to a point where prevailing winds could carry them back to Spain.
The Gulf Stream originates, fittingly enough, with the strong currents flowing into the Gulf of Mexico from the Caribbean, then moves eastward through the Straits of Florida between Florida and Cuba, where it’s called the Florida Current. It then joins the Antilles Current and flows north along the southeastern coast of the United States.
When the Gulf Stream encounters North Carolina’s east coast at Cape Hatteras, it begins to turn eastward, eventually running into the Labrador Current off Newfoundland, where it creates heavy layers of fog over the ocean. In this area, the Gulf Stream has now lost much of its warmth and becomes the North Atlantic Current, which crosses the Atlantic on prevailing southwest winds and begins to turn south near the coast of Europe. There, it joins with the Canary Current to form the North Equatorial Current. Now the cycle begins again as the North Equatorial Current heads west toward the United States again.
In the Gulf of Mexico, the Gulf Stream is about 50 miles wide and surges along at about 4 miles per hour, making it one of the strongest currents known. But in the North Atlantic, it slows to only 1 mile per hour and splits into several smaller currents that total several hundred miles in width. At this point, the current moves 500 times more water per second than the Amazon River. The frigid North Atlantic causes the moving water to sink, creating a deep current that keeps the Gulf Stream moving in its constant circular journey.
The Gulf Stream is only one giant whorl of water, although it’s the best known in the United States. There are similar circular currents in the Western Pacific and other oceans. These currents, like the flowing air masses above them, serve to transport heat northward. The earth’s oceans absorb about half of all the solar radiation streaming through the atmosphere, creating a huge source of potential energy. If all this energy wasn’t balanced by the oceans’ heat transfer process, there would eventually be a huge temperature difference between southern and northern latitudes, causing dire and far-reaching consequences for the global climate.
In the middle of the North Atlantic is a gyre. This vast ocean-within-an-ocean is called the Sargasso Sea. Caught between coastal Atlantic currents, its sluggish waters collect seaweed, driftwood, and other floating debris that are home to a multitude of tiny sea creatures.
The scientific term for giant circling currents is “gyre.” Five gyres dominate the planet’s oceans, one each in the North Pacific, South Pacific, North Atlantic, South Atlantic, and Indian Ocean. Because of the Coriolis effect (for details, see the section titled High Pressure and Low Pressure), the water circling around each gyre tends to deflect to the right. This has the effect of moving the water inward, creating a dome of water at the center of each one. There may be a difference of only a few feet between the height of the dome and the gyre’s edge, but that’s enough to make the surface water eventually flow back “downhill,” where it joins and reinforces the stream’s current.
Even though the Gulf Stream and other ocean currents are permanent features, you won’t always find them in exactly the same place. Not only do they tend to meander a bit, but occasionally an eddy will break away and go spinning off by itself, carrying the characteristics of the region where it formed to other parts of the ocean, just as an air mass does in the atmosphere. Scientists can sample water from one of these large whirlpools and learn where it originated. In fact in one case, small surface eddies from 500 miles off Cape Hatteras were found to have begun in the far eastern Atlantic near Gibraltar, more than 2,500 miles away!
When we think of currents we think horizontally, but there are vertical currents in the ocean, too, known as upwellings. When surface waters are moving away from each other, or diverging, more water from underneath comes up to replace them, usually bringing colder, nutrient-rich water to the surface. Fish go where the food is, so upwelling can make a summertime fishing expedition a more rewarding experience while also cooling nearby shores. Upwelling usually occurs near a coastline, where winds blow surface water away from the shore. When the waters are blown back toward the coast, downwelling can occur as surface water gets compressed against the shore and sinks toward the bottom.