|Bearings by Thomas Yocum|
The Atlantic Coastline:
’‘There is a river in the ocean,’‘ wrote oceanographer Mathhew Maury in
1855. ‘‘In the severest droughts it never fails, and in the mightiest floods
it never overflows; its banks and its bottom are of cold water, while its
current is of warm; the Gulf of Mexico is its fountain, and its mouth is the
Arctic Sea. It is the Gulf Stream. There is in the world no other such
majestic flow of waters.’‘
Maury's writing reflected the spirit of discovery that held the scientific world in its grasp throughout the 19th century. Scientists struggled to understand and explain the unfolding revelations 400 years of European exploration provided. Most of the exploration involved ocean travel, and despite the millions of miles logged by mariners, early scientists knew little about the vast watery expanses.
Probably no other feature of the oceans of the world was more scrutinized, studied, and sailed upon than the warm, blue waters of the Gulf Stream. By the time Maury penned his now-famous ‘‘river in the ocean’‘ line nearly 150 years ago, scientists were convinced they knew most of what was to be known about it. They were wrong.
From space, the broad expanse of the North Atlantic Ocean spreads from the Arctic Circle to the Equator and from North American to Europe. Under its surface great mountains rise up from the Mid-Atlantic Ridge and the Puerto Rico Trench plunges more than 28,000 feet to the ocean floor.
The North Atlantic is famous for its fury and the fickleness of the its weather. Brutal storms sweep across its northern reaches. Endless calms haunt the Horse Latitudes and the Sargasso Sea across its middle. Reliable trade winds blow east from the African coast along its southern limits, pushing early sailing ships and modern hurricanes.
For centuries, men have struggled to learn more about the Gulf Stream. Each generation seems sure it has figured it out. Maury's ‘‘The Physical Geography of the Sea and Its Meteorology’‘ sought to explain the Gulf Stream and the many faces of the North Atlantic. Nineteenth century oceanographers saw the changeable nature of the North Atlantic as a jumbled array with many parts. Today's scientists see the parts as pieces of a larger system they are still trying to understand.
The energy of the sun, the pull of the moon, and the rotation of the earth spin the waters of the North Atlantic clockwise like a giant wheel. At the center of the wheel is the Sargasso Sea, a calm hub in the middle of the spinning water. Along the edges of the wheel run great currents -- the North Atlantic, Canaries, Equatorial -- and the most famous of all, the Gulf Stream.
The Gulf Stream is not born in the Gulf of Mexico as its name suggests. Rather, its waters have traveled across the Atlantic as part of an ocean-wide system. Along the Equator, the elements of the Gulf Stream begin to take shape. Flowing from the east, the South Equatorial Current splits in two when it hits the tip of Brazil. One-half of the current moves north along the coast of South America where it is joined by the full force of the North Equatorial Current.
Continuing northwest, the huge push of water again branches as it approaches the Caribbean Basin. The larger branch, the Antilles Current, moves north and east along the Antilles and Hispanola. The other runs west, past the Caribbean Islands and Cuba and through the Yucatan Channel and into the Gulf of Mexico. It is this branch of the current that helps give the Gulf Stream its distinctive characteristics.
Warmed by the sun in the shallow waters of the gulf, the water rushes east through its only escape, the narrow Straits of Florida. The straits, only 50 miles wide and 2,500 feet deep in places, help to increase the speed and force of the water. Like a thumb over a garden hose, the narrow straits push the water ahead, sometimes reaching speeds of up to 10 miles per hour. This current -- the Florida Current -- is faster than any other Atlantic Current, carrying a billion cubic feet of water every second past Miami. Deflected to the north by the Bahama Islands, the Florida Current joins the Antilles Current. The Gulf Stream System, as it is now known, triples in volume and pushes north.
The flow of the current moves north along the southeastern United States, slowing as it runs toward Cape Hatteras where it gradually turns toward the east. But the huge wheel of the North Atlantic continues to turn, pushing the still-warm waters off the New England coast and the cold water of the Labrador Current. Off the Grand Banks of Newfoundland, the Gulf Stream and Labrador currents collide, creating heavy fog and often-violent weather conditions. The ocean water temperature changes can be dramatic. One boat reported a 20-degree temperature difference from bow to stern as it crossed from one current to the other.
The cold water of the Labrador Current sinks below the Gulf Stream as it drops of the Continental Shelf, robbing the warmer current of energy and cooling and slowing its speed as it continues east. Most scientists consider this to be the end of the Gulf Stream, preferring to call the current that flows on the North Atlantic Current. The North Atlantic Current continues to flow east and then south, joining with the Canaries Current of the western coast of Europe. There the currents combine to form the North Equatorial Current and completing the ocean-sized outlines of the North Atlantic wheel.
The benefits of the Gulf Stream were discovered early by sea captains. Spanish galleons, laden with the treasure of the New World, used the current as an expressway as they made their passages back to Europe. Early maps of the Gulf Stream were closely guarded secrets handled with the utmost care. Pirates and privateers knew to keep on the lookout for Atlantic armadas along the southeastern United States.
Throughout the colonial era, the Gulf Stream remained the principal ocean route along the southern coast of North America. Trade in rum, sugar and spices fortified the young colonies and was vital to the economic needs of the growing markets. Although the current was a benefit to some ships, it proved detrimental to others pushing west to the New England colonies from Britain.
In 1768, when Benjamin Franklin, then-postmaster general for the American colonies, traveled to London, he was questioned by British authorities about why letters took much longer to get to New York than to New England ports when the two locations were ‘‘scarcely a day's sail apart.’‘ Franklin asked his cousin, Timothy Folger, an American whaling captain, if he knew why.
Folger said American whalers were well-acquainted with the Gulf Stream. They knew whales could be found along its plankton-rich boundaries. They also knew travel back to New England whaling ports could be hastened by sailing north of the powerful push of the current. Folger said Americans had frequently told British captains about the futility of fighting the current, and how to avoid it, but that they had ignored the advice. ‘‘They were too wise to be counselled [sic] by simple American fishermen,’‘ Folger dryly told him.
Franklin asked Folger to sketch the current on a map, which he then had printed and presented to the Lords of the Treasury, who in turn passed it along to their captains. British ships soon began to steer clear of the current when heading west.
Franklin was a zealous observer as he traveled the Gulf Stream during his trans-Atlantic crossings, recording speed, direction and temperature data as he went. Although Franklin was one of the first to conduct a scientific study of the current, he certainly wasn't the last. Throughout the historical record, the amazing nature of the Gulf Stream has astounded those who have tried to understand it.
Maury and his 19th century contemporaries used their state-of-the-art equipment to measure water temperature, buoyancy and current speed information from around the world. He distributed special logs, each with 12 blank pages in the back, to Navy and merchant captains to record data from their travels. Maury and his staff poured over the notes from the crossings and generated the first edition of ‘‘Wind and Current Charts’‘ in 1847.
Captains who were once reluctant to take part in Maury's study began to take notice when crossing times began to be dramatically reduced. One captain cut 35 days off a 110-day journey to Rio de Janeiro. Maury offered the charts for free to anyone who would send in data. Time was money for the sea captains. Maury was on his way.
His work was the foundation for much of the research over the next century. Oceanographers poured over reports of derelict ships and floating debris, a peril to navigation and a treasure-trove of information. As the location of the flotsam was plotted and the drifting debris was tracked, scientists gradually began to realize that currents formed oceans, not the other way around.
The Gulf Stream, they realized, was part of a grander system. Rather than a river in the ocean, they began to see the Gulf Stream as the western edge of the North Atlantic circulation. A powerful current rushing along the edge of a continent is rare on the planet but not unknown. Along the western edge of the Pacific Ocean and the coast of Japan, the Kuroshio Current rivals the Gulf Stream in force and magnitude. Similar to the Gulf Stream, the Kuroshio Current is part of a trans-Pacific system that spins in the same wheel-like North Atlantic, connecting the North Pacific, California and Equatorial currents.
Scientists have continued to study the Gulf Stream using increasingly sophisticated technology. They have found that the composition of the ocean bottom over which the current flows affects it more than previously recognized. As the Gulf Stream pushes north along the southeastern US, bits and pieces of the current break off into enormous whirling circles, or eddies, known as gyres. Scientists believe that gyres are created by the sloping seafloor that rises abruptly in a succession of submerged mountains known as the New England Sea Mounts. The undersea mountain tops shear off the bottom of the current as it rushes by, creating monstrous undersea whirlpools.
Most of the gyres fall away to the east, toward the center of the spinning wheel of circulation. There they can be surprisingly long-lived, some spinning for two or three years. Other track west where they can bathe the coast in a tropical bath of warm, crystal-clear water.
Although Maury's description of a ‘‘river in the ocean’‘ may no longer be correct, at the time it was a milestone of understanding about the powerful forces that lie just over the eastern horizon of the Carolina coast. As technology and science continue to push the limits of our understanding of the forces that shape the Gulf Stream and the world around us, there is little doubt that the marvels of the ocean will continue to surprise and amaze those who take the time to plumb its watery secrets.
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