The Devil in the Deep Blue Sea

First of three parts

Hundreds of miles from any land, the waters of the North Atlantic suddenly developed an oddly deep-blue hue and turned incongruously warm.

Patches of peculiar brown seaweed rode the surface, and the ocean brewed mild, damp winds that the muscular 20-year-old could feel on his skin.

To the sailor, Benjamin Franklin, it was a puzzle, one that would baffle and bedevil him for decades.

It would take him 40 years to figure out what he had encountered back in 1726. He had crossed a moving, meandering mass of warm water, 300 times stronger than the flow of all the rivers emptying into the Atlantic Ocean. It was a force more powerful than a million nuclear plants.

Franklin would call it "the Gulf Stream," following the lead of generations of whalers.

It was a current that over the centuries would conspire to scuttle countless hundreds of ships, hurtle a boatload of Florida-bound Haitian refugees to Nova Scotia, and, more recently, deposit tropical fish on the shores of New Jersey and Rhode Island.

Scientists now know that Franklin had crossed a climate divide, one that made the weather of the New World as different from the Old as the Delaware from the Thames. In the 17th century, William Penn had marveled how the Philadelphia sun was stronger and the days longer, yet the winter air more biting than London's - 700 miles farther north.

Today, on the eve of the 300th anniversary of Franklin's birth, scientists worry that the world is crossing yet another climate divide. They see disturbing evidence of change. All of the 10 warmest years on record have occurred since 1990; after Katrina set new standards for devastation, the hurricane season that ended 19 days ago went on to exhaust the alphabet; water temperatures in the North Atlantic and the Gulf of Mexico have been near record highs; Arctic ice is melting at alarming rates.

Scientists see signs that the grand North Atlantic "conveyor belt," the marvelously complex system that exports the equator's heat toward the North Pole and helps balance the planet's temperature, may be slowing.

"This is going to be one of the big issues facing humans in this century," says Ruth Curry, a researcher at the Woods Hole Oceanographic Institution.

The North Atlantic has become a hot ocean for global-warming research, and the narrow but potent ribbon of current known as the Gulf Stream is at center stage.

Just what is this mysterious force, and why is it so important?

Only in the last generation have scientists come to a deeper understanding of the stream. Now they have a new urgency to find answers - answers that don't come easily, for the stream has been reluctant to give up its secrets.

It has prowled the Atlantic for 60 million years, as inscrutable as it is magnificent.

Of whales and Englishmen

In the 1760s, about 40 years after that first encounter with the mysterious blue water, Franklin was in London serving as deputy postmaster for the colonies - and doing so with the same imagination and energy that he apparently applied to everything.

He had recently introduced an important innovation, a fleet of "packet ships" to deliver mail across the Atlantic. Unlike the heavy cargo ships that didn't leave port until they were full, the packets adhered to schedules. The packets were also lighter and faster than the freighters and used smaller crews.

But a mysterious force was outwitting the great innovator. Inexplicably, the cargo ships were completing the mail runs to the colonies 17 days quicker than the packets. Franklin was flummoxed.

He was told that some of the captains were dawdling because they were unhappy with their pay. He sought a second opinion from his cousin, Timothy Folger, a Nantucket whaling captain and dealer in sperm-whale oil who frequently visited London on business.

Can you explain this, Franklin asked.

Easily, Folger said.

Unlike the savvy freighter captains, the British packet captains obviously knew nothing about the Gulf Stream, which was the lifeblood of his whale hunters. The borders flanking the swift, steady current worked for whales like a superhighway, complete with rest stops. Plankton flourished at the boundaries of warm and cold water. Fish ate the plankton. Whales ate the fish.

In following their quarry, Folger's whalers were tracing the outlines of the Gulf Stream.

The whalers often ran into British packet captains, who evidently were no match for the whales in terms of navigational intelligence. They were trying to buck the stream.

Even with a favorable breeze, Folger told his cousin, "they are carried back by the current more than they are forwarded by the wind." If the mail packets got caught in the stream, that would explain why it took them so long to make deliveries.

Folger's whalers often advised the British captains to get out of the current that they called the Gulf Stream, "but they were too wise to be counseled by simple American fishermen."

The British captains had their reasons for following such a circuitous route to reach New York, says Yale Franklin-ologist Ellen R. Cohn. They sailed so far south to avoid the treacherous shoals of Georges Banks off the New England coast, but had no idea of the east-flowing trap that awaited them on that course. They were following an unaltered British sailing manual published 70 years before.

Franklin threw the book away.

Now, with its outlines sketched by the whales, the Gulf Stream sat for its first serious portrait. Franklin and Folger drew up a remarkably accurate chart whose mean path closely parallels that shown by satellite data today. Franklin included detailed information on how to stay out of the stream's way.

It was a prodigious achievement. Before Franklin's chart, the Gulf Stream had ambushed countless merchant seamen and pirates, but whatever they learned they kept to themselves, eager to keep their competitive advantage in the new global economy.

How valuable that chart would have been to legions of Franklin's predecessors. In 1497, John and Sebastian Cabot might have kept their beer cold. Instead, the current warmed the precious cargo in the ship's hold. Spanish explorer Ponce de Leon might have avoided major frustration. He bumped into the Gulf Stream in 1513, discovering to his dismay that a favorable wind was no match for the stream as he tried to sail against the northbound current off the Florida coast.

Once Franklin figured out the Gulf Stream, he could not leave it alone. Ultimately, his pioneering measurements laid the groundwork for generations of researchers who would try to peel away the stream's deepest secrets.

Testing the waters

On April 28, 1775, with the fate of the 13 colonies in the balance, Franklin was on his way to France looking to enlist help for the burgeoning Revolution.

Along the way, he decided to do something that would change the course of history - climate history.

In the company of two of his grandchildren, he carefully lowered a thermometer into the ocean at 8 a.m. on April 29. He noted an 11-degree jump in water temperatures, from 60 degrees 14 hours earlier to 71 degrees. He knew he was in the Gulf Stream.

Franklin took his measurements four to six times a day, from 7 a.m. to 11 p.m., until May 2.

He would take similar readings every time he crossed the big current.

"I find that it is always warmer than the sea on each side of it," he observed to a French colleague. His advice to captains: Keep a thermometer handy, and use it diligently.

Franklin took measurements whenever he had the opportunity. Seventy years later, Franklin's great-grandson Alexander D. Bache persuaded the U.S. government to take systematic measurements.

The Gulf Stream's true identity would be slow to unfold; key insights came through a series of impressive efforts in the 20th century.

Prince Albert of Monaco, who lived in a resort kingdom where winter was unknown - although it was at a latitude 200 miles north of Philadelphia - had a Franklinesque curiosity. An avid oceanographer, he dropped glass bottles, copper balls and wooden barrels into the ocean from his yacht in the early 1900s. Inside them, he would place requests in 10 languages asking people to report where the objects were found. It is estimated that he sent 1,500 such devices into the North Atlantic.

The returns were startling. The trails of the bottles revealed that the Gulf Stream was part of a wild system of spinning currents. So detailed was his analysis that by the time the First World War ended, he was able to forecast the paths of drifting sea mines.

Oceanographers were getting smarter about the behavior of the Gulf Stream, yet by the mid-20th century, their understanding of what set it in motion was still seriously lacking.

A dream, a stream

The brilliant, Wilmington-born Henry Stommel changed all that. "Why do our ideas about the ocean circulation have such a peculiarly dreamlike quality?" he once asked. In 1948, he took the Gulf Stream out of the dream world.

Stommel came up with equations to explain why the stream was where it was and why it was so swift.

Despite its name, it is not exactly a stream. It is the western flank of an enormous circle of water, or gyre, in the Atlantic. The center of the gyre, however, is well west of the center of the ocean.

Stommel explained why the western side of an ocean basin is different from the eastern side. The planet's spin creates forces that drive currents toward the west. The Gulf Stream is forced through a narrow channel between the gyre's center and the continent, so it flows rapidly. The water to the east of the center, with more room to spread out, drifts to the south leisurely.

Stommel correctly predicted that similar currents would be found in other ocean basins. His Gulf Stream work earned him the title of the father of modern oceanography.

For an encore, he postulated that the Gulf Stream was withholding another secret. It was moving atop a cold, deepwater current that returned toward the equator. Float devices proved him correct. Warm water was transported northward. It cooled, sank, and returned southward in the deep ocean.

The term conveyor belt for this didn't surface until the mid-1980s, yet Stommel had described this important piece of the oceanic circulation that helps the planet retain its temperature balance.

The Gulf Stream was more than an obstruction or aid to navigation. It was a key piece of the climate puzzle.

Thanks in large measure to the Gulf Stream, the Atlantic transports more heat northward than the Pacific, even though the Pacific is three times bigger. The explanation has to do with one of the most prosaic substances on Earth: salt.

Salt makes water heavier, and the Atlantic is saltier than the Pacific. Heavier water sinks faster. The sinking in the far North Atlantic pulls more warm water northward, and that keeps the conveyor moving. Climate researchers worry mightily over the fate of the conveyor. They know that the Gulf Stream holds important clues, but the elusive, ever-restless stream isn't making it easy for them.

Alien stowaways

It is a perfect day to hunt for aliens off the coast of North Carolina. The sargassum grass, brown and floating in swelling clumps, is far more plentiful than the whitecaps interrupting the deep-blue waters. The Gulf Stream is in a particularly relaxed mood today, calm enough to show off its iridescent fingers.

It is not a day to waste a sliver of late-summer daylight, so Paula Whitfield, a scientist with the National Oceanic and Atmospheric Administration who is on the trail of exotic - and invasive - lionfish, is up at sunrise. Lionfish, the first Pacific invaders ever to show up in the Atlantic, first appeared off the coast of Florida in 2000 and have been migrating northward ever since. At 7:15 sharp, she zips up her black wet suit, slips on her flippers, and waddles cartoonishly across the deck of the Nancy Foster to plunge into one of the most challenging research environments on Earth.

The stream's broad outlines were captured nicely by Franklin's tidy arc, but that arc could not explain how Whitfield's quarry from the tropics could end up on the shores of New England.

Scientists now know that the Gulf Stream has been hiding a far more fascinating, unpredictable and complex character than even Franklin could have imagined. Its very nature makes it all but indiscernible: Ocean currents are among science's largest moving targets.

"The biggest problem is the harshness of the environment," observes William Johns of the University of Miami's Rosenstiel School, who knows this from personal experience.

Johns, tall and soft-spoken and a ringer for actor Patrick Stewart, left Chadds Ford to devote his career to studying currents in the Atlantic and the Florida Straits. But the salt air corrodes instruments, storms scatter them to the four winds, and sharks bite into the cables. The work is monumentally tedious, and research vessels expensive.

On the lionfish mission, the Gulf Stream teaches Whitfield and her divers anew that it is restless and unpredictable. It is moody, meandering to the west and lashing the ship with a swift current. It fights Whitfield and her divers 150 feet under the surface. This is the same current that has transformed the waters off the mid-Atlantic into a tropical aquarium. Twice, her divers have surfaced with Caribbean lobster.

Lionfish - spiky, spectacular, and favorites of the aquarium trade - arrived on the East Coast under mysterious circumstances. The best guess is that an aquarium owner dumped two or more into a Florida canal. Once the fish reached the ocean, the Gulf Stream took care of the rest.

Whitfield's colleague, biologist Roldan Muñoz, cuts open a captured female, revealing the dimensions of the potential threat. One female is believed capable of releasing up to 30,000 eggs.

And those eggs float.

Whitfield says it is no coincidence that lionfish sightings closely parallel the paths of the Gulf Stream. They have been sighted as far north and east as the shores of Rhode Island, where the Gulf Stream does not roam. How could that happen?

The stream pinches off into wild eddies on either side. These circular whirlpools, as wide as the stream itself, are the bane of sailboat racers. Lionfish eggs evidently got caught in some that spun toward the Northeast coast.

Whitfield and Muñoz think it's important to figure out how many lionfish the Gulf Stream is carrying. The fish are eating everything smaller than themselves, and nothing is eating them.

The stream, however, will not give up the whereabouts of all the lionfish, and Whitfield knows it. She and her team searched 27 suspected hangouts, a tiny fraction of a 1,600-square-mile area off the North Carolina coast, which, in turn, is a tiny fraction of all the possible habitats.

It is the undercurrent of frustration that attends all Gulf Stream research.

The ultimate riddle

A clearer picture of the stream is slowly emerging from deepwater cables, instrument packs dropped from ships, and robot submarines, but in some cases the stream is teaching scientists only the depths of their ignorance.

They are now well aware that the Gulf Stream is one piece of an immense system, a "spaghetti diagram of tangled, looping, crossing tracks," in the words of science writer Robert Kunzig. It is impossible to say precisely where the stream begins and ends. Its energetic course has been likened to that of a restless snake held by the tail off Florida.

As evidenced by the lionfish, at any given time the stream's borders might be framed by several large eddies 50 to 100 miles wide. In satellite images, the gyrating eddy patterns evoke van Gogh's The Starry Night.

The main path of the Gulf Stream moves along at 2 to 6 m.p.h., resembling an immense, albeit serpentine, waterfall. Johns' research has documented that the source of the stream's waters extends all the way to the Brazilian coast and the South Atlantic.

The stream pours through the straits of the Caribbean islands and squeezes into the Gulf of Mexico through Yucatán Strait, making the Gulf waters warm and deep. The water swirls into "loop currents," such as the particularly deep one that ignited Hurricane Katrina.

Eventually, the water shoots through the Florida Straits with almost unimaginable force. The volume of water exiting the straits each day would cover the entire city of Philadelphia with a layer of water five miles deep, by Johns' calculation.

Ocean researchers are circumspect, but they believe they are getting a better handle on the stream's day-to-day behavior. They are getting better at understanding how the stream affects storms, and they are using that knowledge in the computer models that forecast weather.

The stream has inspired bigger ambitions in other scientists, who hope it might lead them to the ultimate forecast. If they can detect changes in the stream, it might tip them off to changes in the global climate.

Today, from the frigid seas of Greenland to the subtropics, an unprecedented effort is under way to monitor the turbulent and chaotic North Atlantic to see whether the immense conveyor belt is changing - or breaking down.

Yet predicting the behavior of the Gulf Stream and the world's climate for the next 100 years is a risky proposition.

It's hard enough forecasting tomorrow's weather, and in some dramatic instances, you can blame the Gulf Stream for that.