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Praise for To Follow the Water
“Murphy calls on his storytelling skill, his understanding of history, and his ability to explain complex science without dumbing it down. He succeeds at all three.”—Offshore
“Romantic, accessible work that makes difficult concepts like water-mass movement engrossing and inspiring. . . . Murphy has done an enormous service for general readers interested in the science and politics of climate change by asking and, more importantly, re-asking detailed questions until he can produce jargon-free explanations.”
“Many books exist on climate change but none as approachable as this.”—Library Journal
“Scrupulously researched and excitingly presented.”—Booklist
AS THE STORY GOES, a promising young doctoral candidate in physical oceanography sits nervously at his oral exam before a committee of prominent ocean scientists. Instead of quizzing him on the principles of ocean circulation, one of the elder scientists, a famous figure in the field, asks: “Now that you’ve completed your course work and have been to sea aboard research vessels, how would you describe the oceanographer’s primary job?”
Surprised, the student pauses, ponders, and replies: “To follow the water.”
When I first heard the story, I understood that it was probably apocryphal, a device composed consciously to sum up the science. But at the time I didn’t fully appreciate its implied point: that “to follow the water” is a lot easier said than done. As Carl Wunsch, an actual famous figure in the field, put it, “One of the reasons oceanography has a flavor all its own lies in the brute difficulty of observing the Ocean.”
“Come on,” said Chief Scientist Molly Baringer, gathering audi“ence members from both labs for tonight’s movie, that climatological dust-up The Day After Tomorrow. “It’ll be fun.”
This was our last night out after thirty days at sea aboard the research vessel Ronald H. Brown, now steaming for her homeport of Charleston, South Carolina. All aboard were weary, glassy-eyed, and ready to walk on solid Earth. I was thinking about having a last look at the nighttime ocean, then bed. “Is this like the Italian kids who go to the opera to boo the tenor?” I asked.
“Exactly,” said Molly.
It was a hot ticket. The audience—officers, crew, technicians, volunteers, and scientists—overflowed the chairs in the ship’s lounge onto the floor, shoulder to shoulder. We could tell from swelling minor-key background music as the credits rolled that something bad was about to happen. Our hero, Jack, a climatologist with the National Oceanographic and Atmospheric Administration (NOAA) is speaking at a climate-change conference in New Delhi, India, where it is snowing. Jack warns the audience that if we continue our greenhouse gas emissions, global warming will melt the polar ice caps, and all that freshwater will sever the worldwide ocean circulation. If that happens, then we’re looking at another ice age.
Someone asks Jack to explain the seeming paradox. How can global warming cause an ice age? Our climate, Jack begins, is highly fragile, and the ocean—But he is interrupted by the trollish U.S. vice president, intentionally resembling Dick Cheney, who snarls, “Our economy is also fragile. You scientists [intoning the word as it were syphilitics] would do well to remember that.”
The exchange doesn’t get far before Jack, not one to suffer fools, shouts back, “Mr. Vice President, if we don’t act now, it may be too late!”
Well, of course it’s already too late.
Cut to: mega-tornadoes tearing through Los Angeles, obliterating the Hollywood sign and other symbols of civilization. Reports of disaster are reaching NOAA headquarters from all over the globe. Sea levels have risen twenty-five feet in half an hour; hurricanes are forming over land; a five-story wall of water submerges Lower Manhattan, sweeping away East Coast icons of permanence. Finally, giant storms cover the entire Earth. When they clear, Jack pronounces, “We will be in a new ice age.”
We were amused that Jack was a NOAA scientist. The Ronald H. Brown is a NOAA ship (pronounced “Noah”), Molly a real NOAA scientist. To understand the long-term circulation of the North Atlantic as it relates to climate change had been the purpose of this expedition, now concluding with computer-generated images of climatic doom. The real scientists giggled or moaned softly at the oceanographic gibberish between Jack and the other cinematic scientists, but in the darkened room, once the “science” had been dispensed with, the ship rolling gently, they began to nod off. Just before joining his colleagues in sleep, the German ocean theorist Jochem Marotzke sitting beside me turned and said, “All this, it’s nonsense, of course. But at least the movie puts the ocean into the climate.”
I escaped a headache from the Doomsday din and the soggy human part of the plot by fleeing topside. White caps rolled out beyond Brown’s quarter wave, but with the wind, the Gulf Stream, and the ship all heading in the same northerly direction, her motion was subdued, almost gentle.
The ocean has been left out.
Yet a concept of climate that ignores the ocean makes no more sense than one that excludes the air. Flowing great distances, like global blood vessels, ocean currents stabilize our climate by transporting heat from where there is too much to where there is too little. One reason why the ocean has been left out of the climate-change discussion is that its internal mechanisms and its interactions with the atmosphere are stunningly complex. That the ocean has been left out has helped pitch the discussion toward unproductive, distracting extremes—either global warming is bunk or sea levels are about to rise twenty feet—and to frame the issue as if it were a matter of opinion, like the place of prayer in public schools.
Climate and climate change are strictly matters of science. Only scientists can figure out what is actually going on; only they can inform us. And only from oceanographers can we learn anything real about the ocean’s role in climate. But as yet, and for various reasons, we don’t talk very effectively with scientists, or they with us. This book seeks to aid the cause of communication by introducing the ocean’s astounding dynamics and the bright people who devote their lives to understanding its ways and means. This, then, is a story of discovery—first, for the sake of context, by marine explorers, but mainly by scientists. Here and now, oceanography has “come ashore,” its practioners’ interests and ours intersecting around the climate we all share. Scientists haven’t simply discovered the role of the ocean in the complex network we call climate; more than that, they are beginning to employ oceanographic techniques to predict climate change.
I can hear my friends in the field caution against overstatement. They aren’t quite able to do that today, but they will be, if not tomorrow, then the day after. The time has come to talk.
Let’s say, arbitrarily, that in the year 700 A.D. a monk is strolling a rocky crescent beach at the mouth of Bantry Bay in the far west of Ireland. The tide is coming in fast, and a scatter of rain is starting to fall. About to turn back, he notices something peculiar in the line of wet, black sea wrack at the high-tide line, and he picks it up. It is a heart-shaped bean with a hard, shiny brown shell about the size of a child’s fist. He dries it, turns it over in his hand, and holds it to the light. He has never seen such a thing before. Did it come from lands across the Western Sea? Or from beneath the sea, the fruit of some aquatic plant ripped from its roots during yesterday’s westerly gale? Is it a sign, a symbolic heart? He squints out at the horizon as if for an answer. Finding none, he glances back at the shiny little heart in his hand and marvels still again at the ineffable mystery of God’s creation.
The sea-heart bean, technically Entada gigas, originates in the tropics where, the monk’s Bible tells him, the seas boil, but enough sea-hearts made the ocean crossing to have been used as teething rings in medieval Europe and hollowed out to make snuffboxes during the Enlightenment. Ground to powder, they were taken as a tea to relieve constipation. Midwives used them as talismans in birthing rituals, blessing with good fortune infant and mother by carrying gigas so many times around the birthing bed in the direction of the sun, or something like that. Having come from across the unknown, the unknowable sea, they were attributed magical powers (or in the case of constipation, efficacious results). We called them lucky beans in southeast Florida where I grew up.
Other drift objects crossed the Atlantic and fetched up on the shores of Great Britain, Ireland, Spain, and Norway, coconuts and another variety of Entada, but none was so nautically well found as gigas for the voyage, its seed surrounded by a thin airspace for buoyancy and encased in a hard, impermeable shell for watertight integrity. The robust vine thrives on hundreds of sun-bright riverbanks between the Costa Rican rain forests and the Orinoco Delta, festooning its host trees with extravagant six-foot-long seedpods (Costa Ricans call them “monkey ladders”). When the season is right, the vine drops its pods to the forest floor or directly into the river, releasing the seeds. Most fetch up somewhere downstream. But to begin the long transatlantic voyage all gigas needs to do is reach the sea, where it will fall under the influence of the Caribbean Current that sweeps westward across the sea.
If gigas avoids lurking obstructions—the prominent bulge of the Mosquito Coast, the exposed reefs and sunbaked shallows between Nicaragua and Jamaica—if it hangs in the middle of the sea, then it will ride the current for nine hundred miles, all the way to the Yucatan Channel, the eighty-mile chokepoint between Mexico’s Yucatan Peninsula and the western tip of Cuba. The full flow of the Caribbean Current, which has sprawled across the entire basin, must now squeeze through the bottleneck. When that happens, the physical laws describing the behavior of fluids require that the velocity of flow increase, just as it increases in a garden hose when you narrow the nozzle with your thumb. Gigas is swept right along, into the Gulf of Mexico.
Geography offers to water only one exit from the Gulf of Mexico, and it’s called the Straits of Florida. Huge masses of water blast at dazzling velocity though this half-pipe trench between the arc of the Florida Keys and the north coast of Cuba. The straits bend northward and, like riverbanks, direct the flow between the Bahamian shallows on the east side and the mainland coast of Florida on the west. (If it really were a river, it would contain a volume of water eighty times greater than all the rivers on Earth combined.)
This is the birthplace of the Gulf Stream, the most studied, investigated, probed, measured, and pondered strip of saltwater on the globe. Here in these tight reaches it’s technically called the Florida Current, but that’s just a matter of agreed-upon nomenclature. It’s the Gulf Stream, and it’s flowing north at three or four knots, sometimes five. One billion cubic feet of seawater blow past Miami, Ft. Lauderdale, and Palm Beach every second. Remaining in the axis of the current away from the countercurrents that form on the inshore side of the Stream, the monk’s gigas could cover 120 nautical miles a day (139 statute miles) by doing nothing but floating.
North of Grand Bahamas Island, the eastern “bank” of the Stream vanishes when the chain of shoals, reefs, and low-slung cays slide abruptly into deep water. Now with room to stretch on the seaward side, the current slows somewhat and widens, and the volume of transport nearly triples (to about 150 million cubic meters per second) as it draws in slightly cooler water from the Sargasso Sea and bears gigas north past the coasts of Georgia and South Carolina. Yet the Gulf Stream in this stretch is still constrained by land. The western “bank,” in the form of the continental shelf, remains. At the latitude of Charleston, the shallow, sprawling shelf edges the axis of the Stream one hundred miles offshore. In fact, all the way back upstream to the Yucatan Channel, the current has been shaped, squeezed, or steered by land. While that “River in the Sea” is an overworked and somewhat reductive metaphor, it’s appropriate insofar as it implies the presence of solid banks. If it chanced to avoid the snags, continents, and countercurrents, gigas would likely make it
Origins of the Gulf Streamall the way to Cape Hatteras. But there everything changes. The Gulf Stream puts to sea at Cape Hatteras, casts off all terrestrial association, and it will never again approach dry land.
In technical language, the Gulf Stream becomes a “free zonal jet” at Cape Hatteras. In utterly unscientific language, it seems to celebrate liberation with exuberant display. It wavers, undulates, and meanders. Over time, its net transport remains northeastward toward the Grand Banks. But in the short term, there’s no predicting its whims. Today it might be a (relatively) simple, seventy-mile-wide jet of hot water flowing from west to east between the cold continental shelf water south of New England and the warm Sargasso Sea. Within a week, it might meander north or south, spurt to four knots, and then change its character from a narrow, unified stream to filaments of current flowing at different speeds. Then again by the end of the month, it might have reformed onto a straightforward easterly course lazing along at two knots. Or not.
And so the sea-heart bean, having drifted more than two thousand nautical miles, now faces its greatest “peril.” Any of those meanders might cast it into the Sargasso Sea or out into the cold continental slope water to the north where even an evolved drifter like gigas will rot and finally sink. Likewise, gigas might be entrained in one of the huge eddies cast off by the main flow and go around and around, getting nowhere until it meets the same end. And then there is that other intrinsic impediment: Contrary to popular belief, the Gulf Stream does not go to Europe. This is no technicality, nor a matter of nomenclature like the Florida Current. To reach the shores of Ireland, Great Britain, or Norway, gigas must find its way into the North Atlantic Current, a sort of offshoot current from the Gulf Stream. The North Atlantic Current flows in fanlike tendrils of warm, salty water drifting languorously along the west-facing shores of Europe.
It is not in the nature of currents to end, as rivers end when they empty into the sea. That would fly in the face of a most basic law of nature, the conservation of mass. Having flowed in, water must flow out. The North Atlantic Current does not end when it delivers its warmth and its drift objects on the shores of Western Europe. The current in some partially understood pattern circles the Arctic waters where, chilled in winter, it sinks to become part of the complex, near fantastical deep circulation. Likewise, the Gulf Stream does not end near the Grand Banks where it sheds the North Atlantic Current. Remnants of the Gulf Stream meld into the slow, broad south-setting Canary Current. When it reaches the tropics and falls under the influence of the Trade Winds, the Canary Current bends westward melding into the North Equatorial Current, which sets back across the Atlantic, through the Windward Islands passage and into the Caribbean Sea—to complete the circle. How many sea-heart beans, after a year at sea, fetched up at the mouth of the very river from which they issued? Probably not many, but some, no doubt. The system is circular, and nature loves circles, perhaps nowhere so much as in the oceans.
North Atlantic Surface Currents
THE SEA OF DARKNESS
Even Geoffrey Chaucer (1343-1400) needed a survival gig to make ends meet before he hit it big with Canterbury Tales, and as these things go, his wasn’t onerous—serving the royal household as a sort of high-level clerk and tutor combined. As part of his duties, or because he wanted to, Chaucer taught navigation. He had been interested in it all his life and referred to himself as “an unlearned compiler of old astrologians.” These days, astrology doesn’t come up very often when the subject is navigation, but in his day few Europeans thought of it in modern terms as a set of practical techniques to fix a ship’s position in the open ocean. Under the syllabus of navigation, Chaucer told fantastic stories about mythic figures in imaginary oceans, because in the fourteenth century almost no one had ventured out into the real ocean. The Vikings, of course, had crossed the Atlantic, settling in Iceland and Greenland, and then sailed on to “discover” America in about the year 1000. But the Vikings did not record their discovery; nothing came of their settlements in Newfoundland or in Greenland, and Chaucer may never have heard of the Viking voyages.
Among his more enthusiastic, if unlikely, students was Princess Philippa, John of Gaunt’s daughter and King Edward III’s grand-daughter. When Philippa became queen of Portugal by dint of marriage, she passed her navigation knowledge and her enthusiasm on to one of her young sons by the name of Henry. Exaggerating only slightly, one might say that the era of Western expansion we now call the Great Age of Discovery began with this young boy listening to his mother tell stories about the sea and the heavens she’d learned from Geoffrey Chaucer. The young student grew up to become Henry the Navigator.
Early in the 1420s, Henry founded the famous institution at Sagres, where Portugal shoulders its way out into the open Atlantic, “his great prototype of modern exploration,” as historian Daniel Boorstin described it. A personally opaque fellow, Henry wrote nothing and, famously, never went anywhere. The only portrait I’ve ever seen shows a dark and brooding countenance exuding stern Christian rectitude. Henry had fought in the Crusades at the Battle of Cueta, and, celibate all his life, he died wearing a hair shirt. On the one hand, he was the stereotype of a medieval prince, on the other, a paradigm of Renaissance humanism. Clear-eyed and pragmatic, Henry ignored prevailing Christian dogma about boiling seas and terrible monsters and, presumably, old astrologisms. Sagres was to be a sort of marine think tank, and in staffing it he ignored prevailing racial prejudice by inviting Jews, Genoese, Venetians, Germans, Scandinavians, Arabs, and Muslims, the finest cartographers, navigators, shipbuilders, and scholars from all over the known world, anyone who could help him fulfill his purpose.
Frustratingly, we don’t know precisely what his purpose was. The simplest and most likely explanation was that he wanted to find a sea route to the East. Asia was well known to Europeans, who viewed it jealously and with un-Christian avarice. The East possessed everything Europeans wanted but had none of: pearls, satins, gold, silks, and spices, especially spices. The East even had the Garden of Eden, assumed at the time to be a real place. Asian goods had been trickling to the West over the ancient Silk Road to the end of the line at the eastern shore of the Mediterranean. From ports in present Lebanon and Israel, Italian middlemen distributed them to market, and the merchants who made their fortunes in the spice trade bankrolled the flowering of the Renaissance in Italy. Marco Polo had thoroughly stoked Europe’s hot ambition for things Asian when, in 1295, he returned to Italy after spending seventeen years in China, and published Travels. His great journey and its first-person account showed those at home that the East was even grander, greater, and wealthier than they had imagined. But then shortly after Travels hit the best-seller list, the Moors closed the Silk Road due to the recent religious unpleasantness. Just like that they choked off Europe’s only access to those things Europeans would not live without. The search for a sea route to Asia would become the whole point behind the unprecedented European expansion that Henry was pioneering. But Henry never said he was looking for a sea route to anywhere particular.
However, his strategy suggests that he had a specific idea to test. Between 1424 and 1434, he funded and dispatched fifteen voyages—all in the same direction, southward down the coast of Africa. It’s possible he did so because no one had been out that way before; no European had ever sailed across the equator, nor even reached the tropics by ship. It’s possible Henry established Sagres simply to satisfy his princely curiosity. But many historians believe Henry had surmised somehow that Africa had a bottom and that a ship from Europe could sail around it into the Indian Ocean. If so, his notion flew in the face of conventional fifteenth-century cosmology.
In the second century, Ptolemy, an Alexandrian Greek who liked symmetry, drew a map depicting the world as a single landmass consisting of Europe, Asia, and the northern (the known) part of Africa. For the sake of balance, Ptolemy connected the southern part of Africa to another huge landmass he made up from scratch. Terra Australis Incognito, the great (unknown) Southern Continent, spanned the bottom of the world and reached northward into the subtropics, turning the Indian Ocean into a very large landlocked lake. If that were the case, then of course you couldn’t sail into the Indian Ocean from Europe. No one questioned Ptolemy’s map, until Henry, if that’s what he was doing. In any case, Henry’s voyagers went looking in that direction.
None got very far, none reached the equator, though they discovered the Azores and Canary Islands. However, Henry’s concept and methods were far more important than his geographic accomplishments. At a time when common seamen suspected that necromancy controlled the compass and sea monsters ate Christians in the “Torrid Zone,” Henry sought only observed, empirical facts. Henry wanted data. To get them to go and gather data, he berated, cajoled, threatened, and overpaid timid captains to swallow their fear and sail down the coast of Africa, see what they could see, and then come back and tell him about it. He conceived of exploration as a progressive, collaborative, federally funded endeavor in which no single expedition needed to reach the goal or answer all the questions. Each needed only to press a little farther south than the former and return with fresh knowledge to aid the ensuing expedition. That’s what Boorstin meant by the prototype of modern exploration, and the concept of progressive discovery through accumulated data sounds rather like that underpinning today’s oceanographic expeditions.
If the Sagres concept depended on data acquisition, then these captains needed to record it in a comprehensive and systematic form. At first they were bringing back sloppy, incomplete records, or worse no record, which was tantamount to not returning at all. Henry therefore mandated that his captains write down in standardized form everything they had observed about prevailing winds, currents, potential harbors, rivers, watering sites, wildlife, natives, everything. Henry thus invented the logbook, a giant step in the advance of ocean knowledge. Some historians caution us not to get carried away viewing Sagres from too modern a perspective. Not much is known for certain, and Henry’s voice is nowhere to be found. Maybe it’s stretching the point to see in Sagres the germ of the contemporary oceanographic institute, but it’s not baseless.
However, the concept did not develop, and Sagres died with Henry. He had been gone twenty-eight years when, in 1487, Bartolomeu Diaz dropped his hook in Lisbon harbor mud and proclaimed the triumphant news that Africa did, indeed, have a bottom offering free, open passage into the Indian Ocean to any man with the nerve to make the trip. Diaz would have been that man, except that his crew threatened to throw him over the side if he tried to take them any farther. He named the bottom of Africa the Cape of Storms, objectively reflecting his experience, but the crown, disapproving from a morale standpoint, renamed it the Cape of Good Hope.
Now there was no question about the objective and motivation of exploration. This new generation of explorers would be of a different stripe than Henry. Vasco da Gama, who actually reached India using Diaz’s route, Columbus, Magellan, and the rest were men in a rush, hard, practical, ruthless, ambitious, unrelenting, and they didn’t give a damn about data. Crossing oceans in the 1400 and 1500s was a dirty, dangerous business; living conditions were execrable, the food worse; sanitation was nonexistent; and it took forever. Fatal disease was so rampant that ships were customarily over-crewed by fifty percent to compensate for the inevitable loss; and, of course, the overcrowding nurtured the diseases that killed sailors. Money was the only rational reason to brook that level of misery. To bring a shipment of cloves, pepper, nutmeg, or cinnamon—just one little shipload—back to Europe from the Indian Ocean or the East Indies (present Indonesia) would make a lowborn captain famous and fortunate, this in a society that had never before offered legal upward mobility to his sort.
- On Sale
- Jul 31, 2008
- Page Count
- 296 pages
- Basic Books