A world without ice

The ice was here, the ice was there,
The ice was all around;
It cracked and growled, and roared and howled,
Like noises in a swound!
— Samuel Taylor Coleridge
The Rime of the Ancient Mariner

In late May of 1768, Lieutenant James Cook, a young officer in theRoyal Navy of King George III of England, received an unusual assignmentfrom the British Admiralty. He was to sail to the South Pacific onHMS Endeavour to make astronomical observations of the planet Venusas it passed directly between the Sun and Earth, an orbital event thatwould take place in early June of the following year. Such a passage,known as a transit of Venus, eclipses a very small circular area on theface of the Sun that appears like a shadow moving across the solar disk.This astronomical phenomenon offered a method of estimating the distancebetween the Sun and Earth, by simultaneous observations of themoving dark spot from different points on Earth. Cook was to make his observations on the island of Tahiti in the Pacific Ocean, on the oppositeside of the globe from England. The ostensible motivation for thisundertaking lay in the suggestion that an accurate determination of theEarth- Sun distance was important for reliable navigation at sea.The complexities of the motions of Earth and Venus about the Sunmake transits relatively rare events, coming in pairs separated by eightyears, but with more than a century separating one pair from the next.After the 1761/1769 pair, the next chances to observe a transit would comein 1874/1882 and 2004/2012. Cook had been selected for this scientificundertaking because of his skills in surveying and charting, honed a decadeearlier on the St. Lawrence River, during the Seven Years’ War betweenBritain and France for control of the territory that would become Canada.Endeavour was a small ship, just a little longer than a modern railwaycoach, but home to eighty- five seamen and another dozen officers andaccompanying naturalists, plus their equipment, water, provisions, andgrog. The voyage from England to Tahiti followed a route south throughthe Atlantic, around Cape Horn at the tip of South America, and thencewest into the Pacific to Tahiti. The full journey totaled roughly twelvethousand miles, equivalent to about half the distance around the globe.Under sail it took almost exactly eight months to reach Tahiti, includingprovisioning stops in Madeira and Rio de Janeiro, and some specimencollecting in Tierra del Fuego.

Cook was meticulous about the health of his crew, as the scourge ofscurvy was already well known on long voyages. He knew that diet wasimportant to health, and he carried an ample supply of sauerkraut to wardoff scurvy. The crew, had they known of it, would have lobbied hard forthe anti- scorbutant that Dutch sailors preferred: white wine. It is not clearwhether Cook was aware of the prophylactic powers of wine, but he clearlyknew the perils of having alcohol- incapacitated seamen. Christmas Dayof 1768, celebrated off the coast of Patagonia, was marked not by religiousservices, but by a crew pursuing total inebriation. One of the naturalistsremarked that they were lucky the Christmas winds were light.

Endeavour arrived in Tahiti in mid- April of 1769, in ample time toprepare for the astronomical observations. Cook selected a place to conductthe measurements— on a sandy beach not far from the present- daycity of Papeete. He called the place Point Venus. When I visited Papeetea few years ago I was keen to see this famous scientific spot, but I worriedthat in the more than two centuries since Cook was there, the placemight have lapsed into nothingness. I asked a taxi driver if he had everheard of Point Venus. Yes, he replied, he knew it well. Skeptical that itwould be so easy to find this historic place, I queried him further. Yes,yes, he knew the spot. So I asked him to take me there, and fifteen minuteslater we arrived. It was Point Venus all right— but today well knownas a popular nudist beach! Incidentally, there is also a small monumentto Captain Cook’s 1769 visit.

WHILE THE TRANSIT of Venus was the announced scientificrationale for this voyage, Cook’s sailing orders from the Admiraltyhad another component, designated as secret and not to beopened by Cook until he was at sea. These orders addressed Endeavour’sassignment after the astronomical observations had been completed.They revealed that Cook was to search for Terra Australis Incognita, ahypothetical southern continent that had supposedly been dimly sightedin high southern latitudes by earlier mariners.The notion of a southern continent had been promoted through philosophicaland aesthetic arguments by Aristotle and later Ptolemy twomillennia before the Age of Exploration. They believed that symmetryand balance were inherent characteristics of the natural world, and thatEarth, as a natural object, must surely display these qualities. Such beliefsrequired the existence of landmasses in the Southern Hemisphere to balancethe extensive landmasses of the Northern Hemisphere.Not long after the transit was over— only six hours after it began—Cook took Endeavour southward in search of a southern continent.

Sailing south in the peak of the Southern Hemisphere winter quicklyled to cold encounters with widespread sea ice, and it did not take longfor Cook to realize that it was not the right season for a course into highlatitudes. In September he headed west and encountered today’s NewZealand. He proceeded to circumnavigate and chart the coastlines ofboth the North and South Islands, demonstrating that they were not alarge southern continent, as had been surmised by earlier explorers. Thereturn to England was by way of Australia, where Endeavour narrowlyavoided disaster on the Great Barrier Reef, then onward to the EastIndies, where several crew contracted malaria, and around Africa to theAtlantic, before heading north on the last long leg home. In the Atlantiche encountered some American whalers, and stopped to get news of thelast three years— he learned that Europe was, for a change, at peace.Cook arrived in England in the summer of 1771, with no sighting ofTerra Australis Incognita to report.

The return of Endeavour was celebrated and acclaimed widely, butthe focus was not on Cook, the modest master of the vessel. In thelimelight was the young patrician naturalist Joseph Banks, well versed inmanipulating the press to his advantage. Within just a few weeks, Bankshad worked up a frenzy of public adulation in the press that culminatedin his announcement that there would soon be a second voyage of explorationand scientific discovery, under his leadership. Incidentally, Bankswould insist that Cook undertake the maritime duties, and there waslittle Cook could do to decline. Within a month of his returning homeafter an absence of three years, Cook was already planning the next sailing.His wife, Elizabeth, was not too pleased.

In 1772, by then promoted to captain, the rank by which he is bestremembered, Cook sailed again for the Southern Ocean aboard a newship, HMS Resolution, once again in search of Terra Australis Incognita.On this voyage he headed toward the Pacific by turning east aroundAfrica into the Indian Ocean, and pushing to ever higher southern latitudesas ice conditions would permit. In 1773 he crossed the Antarctic Circle1 three times, at longitudes 40º east, 140º west, and 105º west;each time he encountered impenetrable ice, and came away withoutsighting a southern continent.

His eastward course across the South Pacific, never far from the ice,brought him to the southern tip of South America just as 1774 ended.Early in the new year, he sailed eastward into the South Atlantic, anddiscovered South Georgia Island, a banana- shaped glacier- striped islandthat, at first sighting, he thought might be the long- sought southern continent.But when the distal tip of the banana came into view, he knew itwas just an island. He named it Isle of Georgia, in honor of King GeorgeIII. Continuing eastward, Cook reached the cape of southern Africa,intersecting his path around Africa three years earlier. He had now circumnavigatedthe globe in the southern high latitudes, seldom very farfrom the edge of the ice. Cook noted in his journal2:

I had now made the circuit of the Southern Ocean in a high latitudeand traversed in such manner as to leave not the least room for thepossibility of there being a continent, unless near the pole and out ofreach of navigation. . . . The greatest part of this Southern Continent(supposing there is one) must lie within the Polar Circle where the seais so pestered with ice that the land is thereby inaccessible. . . . I can bebold to say that no man will ever venture farther than I have done, andthat the lands which may lie to the south will never be explored. Thickfogs, snowstorms, intense cold and every other thing that can rendernavigation dangerous one has to encounter, and these difficulties are greatly heightened by the inexpressible horrid aspect of . . . a countrydoomed by nature never once to feel the warmth of the sun’s rays, butto lie for ever buried under everlasting snow and ice.

Cook had clearly disproved the hemispheric “balance” of landmassespostulated by Aristotle, but he demonstrated symmetry of a different type,symmetry not of land but of ice. He had shown that there was a dauntingice barrier in the high latitudes of the Southern Hemisphere, similar to thatencountered in the Arctic. His predictions about the inaccessibility of thepolar latitudes in the South, however, did not stand. In the early nineteenthcentury several sailing ships did indeed sight the Antarctic continent.In 1838, just a little more than a half century after the founding of thenation, the United States sent an expedition to the South Pacific and Antarctic,formally called the United States Exploring Expedition of 1838–43,but colloquially known as the “U.S. Ex Ex.” The expedition was commandedby Lieutenant Charles Wilkes, a naval officer, but was well staffed with scientists,the best known of which was the noted biologist and geologist JamesDwight Dana. In early 1840 the expedition reached the icy barrier along thecoast of Antarctica just at the Antarctic Circle, two thousand miles south ofAustralia. Wilkes traced the coastline for more than fifteen hundred miles,equivalent to the distance from Boston to Miami. Proof that this extensiveterrain was indeed a continent would come later, but clearly the U.S. Ex Exhad encountered a big and continuous landmass.

THE SEVENTH CONTINENT

The symmetry of ice in both the northern and southern high latitudessometimes conveys a false impression that Earth’s polar regions arereally quite similar. The presence of ice, however, actually masks morefundamental differences between the north and south polar regions.The Arctic and Antarctic have been described as being “poles apart,” of course geographically, but also in many other characteristics. The SouthPole lies well within the continent of Antarctica, some 850 miles inlandfrom, and 10,000 feet above, the nearest coastline. The North Pole, bycontrast, is located in the Arctic Ocean, with the seafloor 14,000 feetbelow and the closest coast some 450 miles away. Both poles are set inice, but the thickness of the ice is very different. Beneath the South Polelies more than 10,000 feet of ice, whereas the North Pole sits on a thin10- to 20- foot sheet of frozen ocean water, give or take a few feet. Theice in both settings is on the move, but at very different speeds— at theSouth Pole the ice slips slowly over the pole at a glacial pace of about 30to 40 feet per year, whereas the sea ice of the Arctic is swept along bywind and currents at an average speed of about 3 to 4 miles per day.

Size- wise, Antarctica is a typical continent— smaller than Asia,Africa, North America, and South America, but larger than Europe andAustralia. And it shares many geological characteristics with the othercontinents. The large- scale architecture of all continents is similar tothat of icebergs— continents are composed of rocks, such as granite,that are less dense than the rocks that make up the floors of the surroundingocean basins. Just as ice floats in water, with some ice abovebut most below the water’s surface, continental rocks “float” in rocksof greater density, and stand a bit higher than the rocks in which theyare immersed. The average elevation of the continental surface is somethree miles above the ocean floor, but the low- density rocks of the continentsextend more than twenty miles into the Earth, a continental “root”not unlike the submerged portion of an iceberg in the ocean.

As in the other continents, the Antarctic rocks show the telltale characteristicsof a long and complex geologic history— a wide range of ages,from ancient Precambrian crystalline rocks to very young unconsolidatedglacial deposits. The rock types include the common rock categories—igneous, sedimentary, and metamorphic— and in typical proportions.The Antarctic continent has mountain ranges such as the Antarctic Peninsula,which is really just an extension of the Andes of South America, and the Transantarctic Mountains, which snake across the continentfrom the Weddell Sea to the Ross Sea. Antarctica almost certainly has itsshare of mineral deposits, although none is exploitable, at least for now,because of the extreme environment. Antarctica is, however, unique inone important characteristic— its location astride the South Pole. Virtuallyall of Antarctica lies within the Antarctic Circle, and more than threequarters of its area lies at latitudes greater than 70º south.

How and when did Antarctica come to the South Pole? One mightbe tempted to ask, “Hasn’t it always been there?” but there is ample geologicevidence to indicate that it has not. Sedimentary rocks of Mesozoicage along the Antarctic Peninsula show beautiful fossilized tropicalferns, and Paleozoic- age coal seams in the Transantarctic Mountainsreveal well- preserved low- latitude vegetation. No, Antarctica was notalways at the South Pole— it came there from somewhere else, and fairlyrecently, geologically speaking.

At the beginning of the Jurassic period, some two hundred millionyears ago, the terrain that was to become Antarctica was part of asuper- continental assemblage called Gondwanaland, an enormous landmassthat also comprised the eventual continents of South America,Africa, and Australia, as well as smaller fragments including Madagascar,New Zealand, and India. Gondwanaland itself had been assembledonly one hundred million years earlier, during the closing stages of thePaleozoic era. Following its assembly from predecessor continental terrainsfrom around the globe, this composite landmass received depositsof a unique and remarkably widespread sequence of rock formations,and saw the evolution of a cosmopolitan fauna and flora. Geologists andpaleontologists eventually recognized this rock sequence with its containedfossils as the Gondwanaland signature— the key to recognizingthe full extent of Gondwanaland.

About 170 million years ago, the forces of plate tectonics began todismember Gondwanaland and disperse the pieces. Just as sea ice glidesslowly over the surface of the high- latitude oceans, so also do large segments of Earth’s roc...