Atlantic (48 page)

5. THE LITTLE-KNOWN SEA

The warming of our oceans has its most visible effects on matters great and familiar—on Rotterdam, on hurricanes, on penguins or anchovies. But the rise in temperature, however caused, also seems to work its way into more unfamiliar worlds—and one of them illustrates the notion that it is probably best if we leave the seas alone, because we know much less about them than we think. For there is much currently expressed concern over whether global warming will have a particular effect—whether for good or ill we do not yet know—on a creature that turns out to be probably perhaps the most plentiful species on our planet, and yet one of whose very existence we were quite ignorant until 1986. That was the year when this creature was first discovered, and it was found in the Atlantic Ocean.

The sea teems with tiny drifting beings, plankton, which are suspended, wafting, moving aimlessly among the placid similitude of the world beneath the surface. Where they are and what they do there depends much on the nature of the water on which they waft: on whether it is warm or cold—an attribute that depends on the one hand on latitude, and on the other hand on depth, for they drift inside a three-dimensional universe, whether it is very salty or less so, whether the pressure is high or not so high, whether the sea chemistry is benign or strange, whether it is light or dark—for no light at all finds its way below a thousand meters, and it is perpetually pitch-dark except for vague glimmers from the blooms of bioluminescent creatures and the tiny orange firefly glows from brave beasts that flourish beside the scalding thermal vents. Yet in every zone, from the oxygen-rich splashiness of the coastal waters to the near-freezing blackness and iron-crushing pressures of the deep abyssal trenches, there is almost invariably life, and most of it is microscopic, and most of it is still unknown.

Many of the tiny creatures that inhabit the oceans’ well-lit upper waters emit gas or gaseous compounds. One hard-shelled algal beast,
Emiliana huxleyi
, emits dimethyl sulfide, which some believe contributes to the unique aroma we call the smell of the sea.
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But most, being photosynthesizing animals, suck in carbon dioxide, make carbohydrates, and in immense quantities turn out oxygen. Maybe 70 percent of the planet’s total oxygen comes from such seaborne organisms: one of these was discovered in 1986—a blue-green algae hitherto not known to exist, and which was given the name
Prochlorococcus.

Quite probably the most abundant living creature on the planet, the cyanobacterium
Prochlorococcus
was first discovered in the Atlantic’s Sargasso Sea in 1986. These minute creatures employ their chlorophyll-b to produce as much as one-fifth of the world’s atmospheric oxygen.

A young researcher at the Massachusetts Institute of Technology, Penny Chisholm, first found the creature in the Sargasso Sea. She and Rob Olsen, her colleague from Woods Hole, were on a research vessel sailing from Cape Cod to Bermuda with, as an onboard trial, a machine normally used in hospitals to assay blood and known as a flow cytometer. The principle of this device is simple enough: a laser is shone across a tube through which a fluid flows at speed—blood in hospitals, seawater on Penny Chisholm’s boat—and detectors pick up the light scattered and deflected by any tiny particles, invisible to the naked eye, suspended in the flowing liquid. The two researchers had no idea the machine would even work on the boat; and if it did, they expected to find numerous examples of a particular blue-green algae they already knew existed.

What they did not imagine was that the device would show the existence of millions and millions of even tinier creatures, tiny, oval-shaped living entities, around six microns in diameter, one two-hundredth of the width of a human hair. But these creatures were not simply tiny; once examined under electron microscopes, they were found to have incorporated into their minute workings a type of chlorophyll that permitted them to absorb carbon dioxide and to extract from the seawater a tiny amount of oxygen, which then escaped into the atmosphere.

Taken individually the amount of free oxygen that any one of these algae might produce is microscopically insignificant; but Penny Chisholm calculated that
Prochlorococcus
existed in such unimaginably large numbers—one hundred thousand of them in a single cubic centimeter of water, perhaps a trillion trillion of them in total—that they were quite probably the most common creature in all the world, and would in total produce immense quantities of oxygen.

They prefer to live in the warmer seas, essentially wafting about in the oceans between 40 degrees north and 40 degrees south, or south of a line connecting New York and Lisbon in the north, north of another drawn between Buenos Aires and Cape Town. There they lie, contentedly at the bottom of the food chain, waiting to be eaten by tiny shrimp that would then be consumed by small fish, and on and on, up until the hungriest predators of all, mankind. Or one perhaps should say they probably lie at the base of the food chain, for while it is difficult to imagine anything smaller existing in the sea, Dr. Chisholm felt that
Prochlorococcus
was an example of how nature had once again displayed its infinite capacity, as she put it, to
humble
the world of science, and could readily do so again. Before 1986 we did not know that such a creature existed; now it is recognized as perhaps the most common being on earth—or rather in the ocean—and it plays a central role in keeping land-based creatures alive.

To dramatize this creature’s importance, it can reasonably be claimed that one in every five breaths any human being takes contains oxygen created out at sea, and quite specifically by
Prochlorococcus.
We now know it exists, and it goes without saying that if anything disastrous were ever to befall it, the survival of all beings that require oxygen would be placed at risk. In the two decades since
Prochlorococcus
was found, a great deal of research has been done to see what might harm it, and how. Specifically, researchers have been trying to determine whether the warming of the seas might limit its ability to absorb carbon dioxide and frustrate its propensity for creating oxygen.

It turns out that
Prochlorococcus
seems thus far happily resilient to the warming of the planet. It likes warm seas and flourishes in them. Any increase of the sea’s temperature might well cause the range of
Prochlorococcus
to expand into the newly warmed waters, to push beyond the present day’s 40-degree-latitude lines—and that might have its own effect on not just the outward flow of oxygen into the atmosphere,
but on the absorption of carbon dioxide already in it.

It is tempting—but entirely fanciful—to imagine that such a development might balance some of the expanded emissions of greenhouse gases that are so troubling humankind today. An expansion of the range and population of
Prochlorococcus
might well turn out to be a component of the earth’s self-regulating mechanism, so crucial to James Lovelock’s famous Gaia theory—which holds that the world is to be viewed as a self-contained living being, able to change its own ways and to deal with its changing circumstances. This curious animalcule might be even more precious than at first supposed: not merely supplying the air that we breathe but somehow dealing with our most dangerous pollutant. But this is an idle thought: there is no evidence; a lot of research still needs to be done.

And yet all this concerns a being we were entirely unaware of twenty years after man first went to the moon. Those who have long claimed the sea to be far less known than outer space seem suddenly to have a special brand of wisdom.

•  •  •

The great forces that created the Atlantic in the first place will in time—in a very long time, in human terms—also destroy it. The forces, part of the tectonic mechanisms of the planet, are better understood today than when they were first revealed in the 1960s, but they still present something of a mystery. They are difficult to appreciate in part because they are so complex, but also because of the time scale involved: we are around to witness only the tiny incremental movements and shifts by which the world changes its topography, even though those tiny shifts can often be, for mankind, catastrophically lethal and terrifying.

The earthquakes, eruptions, and tsunamis that have shaken the world during the two thousand years mankind has been able to chronicle them have seemed like gargantuan affairs—death and destruction on what for humans is a titanic scale have been rained down by events that are now a familiar part of history: Lisbon 1755, Krakatoa 1883, San Francisco 1906, Tangshan 1976, Sumatra 2004. Seen in a planetary context, events like these have barely any significance. They are tiny shape-shifts that come to assume real importance only when millions of them, over millions of years, have taken place. The Sumatran tsunami of December 26, 2004, may have killed a quarter of a million people, and may have passed into human history as one of the greatest natural disasters of all time—but it moved the sea floor south of Sumatra no more a few meters northward, and the sea south of Sumatra is many thousands of miles wide. It would take a million years’ worth of submarine Indian Ocean earthquakes before this corner of the world would appear to have changed its appearance even minimally.

It is a fortuitous accident of tectonics that the Atlantic is seismically the least vulnerable of the oceans. The Indian Ocean is scarred by subduction zones and faults, and it was no surprise to the geological community that the 2004 tsunami originated there. The Pacific is almost entirely surrounded by volcanoes and is rocked by ceaseless earthquaking from Japan to Alaska, from California to Chile, from Kamchatka to New Zealand. But the Atlantic, by contrast, has as its geological centerpiece only the Mid-Atlantic Ridge, which is certainly opening up and disgorging lava all the while—but does so in a somewhat lethargic, somnolent manner, and by the standards of the neighbor ocean can hardly be called seismically violent. When Anak Krakatoa was born off the coast of Java in 1930 it appeared with terrible violence and drama; when Surtsey was born off the coast of Iceland thirty-three years afterward it proved spectacular to see but was more a boisterous oozing than a calamitous detonation.

That is not to say there has been an absence of memorable activity in the Atlantic. Much has happened, and the recent occurrences faithfully and fully recorded, more so than elsewhere because sophisticated, organized, scientifically curious, and technologically able man has been living on the shores of the Atlantic for very much longer than around the other oceans.
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There are many early records of violent seismic activity in the eastern Atlantic between Portugal and the Azores, for instance, beginning with a record of flooding in the Tagus in the winter of 1531, and huge waves in the sea nearby that wrecked scores of ill-prepared fishing boats and sailing vessels. Then there was the enormous earthquake that all but destroyed Lisbon on November 1, 1755: it is said to have sent massive sea waves to Madeira and Agadir, as one might expect, but also to have caused destruction as far away as Martinique, in the Caribbean.

The question of whether destructive tsunamis are likely to travel across the Atlantic has prompted some recent concern, ever since the Indian Ocean wave of 2004, which spread rapidly and killed many, from Bengal to Sri Lanka and beyond. The records show few credible accounts of long-distance tsunamis being generated in the Atlantic—the Lisbon event is probably the only one. The Grand Banks earthquake of November 1929, triggered by a magnitude 7.2 earthquake south of Newfoundland, has been studied in great detail—great waves of sand and water, known as turbidity currents, swept down the undersea canyons and severed many of the submarine telegraph cables, the precise thirteen-hour sequence of their failures being recorded by the sudden loss of signal—but it seems not to have created much seismic excitement beyond the St. Lawrence Estuary. Similarly, the immense explosion in Halifax harbor in December 1917, mentioned in chapter 4, did transmit a number of rolling tsunamis—but they lasted only a few minutes and never made it into the open ocean.

A three-hundred-mile long sand deposit running along the east coast of Scotland, between Dunbar and Inverness, is thought to have resulted from a famous submarine landslide off the Norwegian coast eight thousand years ago. And all sorts of mayhem is thought to have been caused on the far side of the ocean when Lake Agassiz collapsed, but no physical tsunami evidence for it has yet been uncovered, even though researchers are hoping to find fossil sandbars on the west coast of the Labrador Sea. Until then the rather tenuous suggestion, already noted, that Black Sea farming patterns changed as a result of the meter-high rise in sea level remains the sole suggestion of transoceanic impact of the great Agassiz flood.

The concern over the possibility that destructive superwaves might be able to cross the Atlantic has come about in part because of what happened in the Indian Ocean in 2004; but in rather larger part it has also spiked because of an item of wild speculation that appeared in the press in 2000—and which held that New York City was at risk of inundation because of an impending landslide on the island of La Palma, in the Canary Islands. News stories in some of the more excitable press—and a lengthy feature film shown by the BBC—had it that a block of basalt the size of the Isle of Man was about to fall off the western side of the Cumbre Vieja volcano, and that the American president should take immediate note lest they be caught unprepared for the devastating effects of a wave that would race westward across the ocean at five hundred miles an hour and, when it struck, would drown major American cities beneath a wall of water scores of feet high.