Dredging The Deep Blue Sea
By Greg Laslo
On a calm blue-skied Sunday morning in early March, a tiny Spanish brigantine flying full sails sailed alongside the HMS Challenger. She had been passing and repassing the larger ship for several days, no doubt wondering about her odd movements. Why on earth would a 223-foot British corvette shorten sail and stop so often with a fine breeze in her favor and the West Indies still a week ahead?
After a brief mid-Atlantic greeting, the smaller vessel was off. With a touch of regret, the Challenger's crew, some 270 sailors, officers and civilian scientists, watched her disappear. First her green hull tucked below the horizon, then her gleaming white sails. Once again, Challenger was left alone with her solitary mission.
Indeed, 22 times during the crossing the Challenger stopped, and her crew furled her sails, unlocked her propeller, and fired up her steam engine. For hours, her officers took soundings, collected 2-liter samples of water from various depths, and returned a scoop of the ooze at the bottom to the surface to the polished wooden deck. Thirteen times, a 137-pound (62-kg) dredge, measuring 54 inches (137 cm) wide with a 15-inch (38-cm) maw, was lowered, and the 2,300-ton (2,070-metric-ton) ship would drift lazily while the dredge nabbed examples of mysterious ocean creatures. Barely two months at sea, the Challenger had already lost seamen to desertion, partially due to the monotony and hard work of all of this "drudging."
"At first, when the dredge came up, every man and boy who could possibly slip away, crowded round it, to see what had been fished up. Gradually, as the novelty of the thing wore off, the crowd became smaller and smaller, until at last only the scientific staff and perhaps one or two other officers besides the one on duty, awaited the arrival of the net on the dredging bridge; and as the same tedious animals kept appearing from the depths in all parts of the world, the ardour of the scientific staff even abated somewhat," wrote Henry Moseley, one of six scientists on board. "It is possible even for a naturalist to get weary of deep-sea dredging."
Of all the reasons it could be famous, the four-year, 68,890-mile (110,224-km) circumnavigation of the HMS Challenger from 1872 to 1876 is best known for its tedium. While scores of individual discoveries were made, including the identification of more than 4,700 new species, the Challenger sailed with orders to survey the world's oceans systematically and methodically. For the men on board, that meant a long, slow voyage filled with days of abject boredom.
Yet, in their around-the-world odyssey, the six-member scientific staff of the ship, four naturalists, a chemist and an artist, changed the way scientists understood the sea floor, species distribution and ocean currents. And most importantly, they carefully published the results, some of which are still studied today, and for good reason. At the roots of those years of drudgery lie the seeds of something new and big: The science they called oceanography.
Exploring the Deep
Scotsman Charles Wyville Thomson learned early in his academic career that he had a knack for the naturalist's field work. As a University of Edinburgh student in the 1850s, he discovered his passion for botany, geology, zoology and ocean science, particularly dredging the depths of the waters off the coast of the British Isles.
"I had long previously had a profound conviction that the land of promise for the naturalist, the only remaining region where there were endless novelties of extraordinary interest ready to the hand which had the means of gathering them, was the bottom of the deep sea," he wrote.
It was an exciting time in science. Darwin's "Origin of the Species" had recently been published, and his narrative on the voyage of the HMS Beagle inspired a generation of naturalists to dutifully set out and catalog the world's creatures.
By the mid-19th century, the dominant school of thought regarding life in the ocean was promoted by English scientist Edward Forbes, a professor of natural history at the University of Edinburgh. He suggested that life was impossible in the deep depths of the ocean. Below 300 fathoms (1,800 feet), one entered the "azoic" zone, according to Forbes.
"Judging from the scanty data laboriously accumulated with imperfect appliances at that time at their disposal, [scientists] had come to the conclusion that life at the bottom of the sea was confined to a narrow border round the land; that at a depth of 100 fathoms (600 feet) plants almost entirely disappeared and animals were scarce, and represented those animal groups only which are among the most simple in their organization; while at 300 fathoms the sea-bottom became a desolate waste, the physical conditions being such as to preclude the possibility of the existence of living beings," Thomson wrote.
However, by the 1860s, telegraph cables ran across the floor of the Mediterranean and Atlantic. In addition to the development of more accurate sounding and sampling methods used to choose the best location for those submerged cables, work on the telegraph led to the discovery of aquatic animals attached to broken cables pulled from more than 1,000 fathoms (6,000 feet).
How did those animals get there? Did they settle to the ocean floor when the animal died, or were they actual deep-sea creatures that debunked the status quo? Norwegian scientist Michael Sars offered his answer. Sars' son had dredged to below 300 fathoms and found life abundant. The crinoids they found were thought to be extinct, practically living fossils. Intrigued, and himself a student of crinoids, Thomson met with Sars to see them for himself.
"Doubts began to be entertained whether the bottom of the sea was in truth the desert which we had hitherto supposed it to be, or whether it might not prove a new zoological region open to investigation and discovery, and peopled by peculiar faunae suited to its most peculiar conditions," he wrote.
He suggested to his friend and collaborator William Carpenter that they undertake some deep-sea work of their own, and Carpenter, the registrar for London University and vice president of the Royal Society, suggested Thomson put his ideas to paper. He, in turn, would present the idea to the society in hopes of attracting government funding for such a venture. In May 1868, Thomson and Carpenter set sail from Oban aboard the HMS Lightning, on course to make a curious discovery.
"A universal and constant temperature of [40 degrees] below a certain depth and varying according to latitude, was at the time accepted and taught by nearly all of the leading authorities of physical geology," Thomson wrote. Why then, did he record several temperatures in the low 30s below 500 fathoms (3,000 feet)? Why did there appear to be "different" water down deep?
Carpenter proposed a theory that opposing currents between the Shetland and Faroe islands were responsible for the differing water temperatures, one carrying warm water northward, the other carrying cold water away from the Arctic. He wanted to return to that area for more detailed measurements, and again the Royal Society delivered. The following summer, Thomson was aboard the HMS Porcupine, dredging the ocean to 2,435 fathoms (14,610 feet) off the shore of Ireland and testing thermometers modified to withstand the intense pressures of the deep.
With two successful voyages under his belt, Thomson accepted a fellowship in the Royal Society and a prestigious professorship in natural history at the University of Edinburgh. But by the summer of 1871, the United States, Germany and Sweden were publicly planning survey voyages that threatened to trump the work of the Royal Society's scientists. Once again, Carpenter proposed the society sponsor an expedition, this time, a circumnavigation of the globe, and it agreed. Carpenter suggested Thomson was the man to lead the expedition.
For the circumnavigation, the Admiralty provided Thomson with the Challenger, a three-masted wooden sailing ship under the command of Capt. George Nares. While the ship would navigate between sampling stations under sail power, she would use her auxiliary 1,200-horsepower steam engine during dredging. Sixteen of the warship's 18 guns were removed to make room for tons of scientific apparatus while miles of dredging and sounding gear occupied nearly her entire foredeck.
According to the society, the mission would have several objectives, including determining the depth of the ocean and collecting bottom samples at regularly placed stations along her route. The crew would collect water, temperature data, and fauna at the bottom, on the surface, and from intermediate depths to answer questions about ocean currents, worldwide distribution of microscopic plankton, and life in the deep reaches of the oceans.
To review those results, a biological laboratory consumed much of the main deck along her port side. There, Moseley, John Murray, and Rudolph von Willemoes-Suhm would dissect, classify and preserve creatures pulled from the depths, as well as those collected on land during time in port. Preserved samples would be stored in her powder locker while at sea, and when land was made, those specimens would be shipped back to the Natural History Museum in London. A chemistry lab for John Young Buchanon occupied her starboard side. Buchanon would measure the gravity and chemical composition of sea water collected at various depths to determine ocean circulation patterns. All told, her scientific quarters left nothing to be wished for, Thomson wrote.
On December 21, 1872, the Challenger and her intrepid crew of scientists cast off from Portsmouth. Immediately, they hit foul North Atlantic winter weather. Within the month, though, the ship had visited Lisbon, Portugal, and was making her way south, following the southern coast of Europe.
Her shakedown attempts at dredging and sounding had mixed results. The sounding line broke three times, and the dredge rope once. This was shaping up to be a tiresome voyage with a monumental task. Finally, between Gibraltar and Madeira, they were successful, at 2,125 fathoms (12,750 feet), the scientists recovered "many interesting animal forms, several of them new to science, and others of extreme rarity and beauty," wrote Thomson in a letter to the scientific journal Nature. One of those was a phosphorescent polyp on a long stem, an octocoral they named Umbellula thomsoni.
Challenger spent the spring and summer in the Caribbean, off the coast of Nova Scotia exploring the Gulf Stream, and crisscrossing the Atlantic. A survey station occurred every two or three days, more often in the Gulf Stream, and when instruments were deployed, progress came to a halt.
"The vastness of the depth of the ocean was constantly brought home to us on board the Challenger by the tedious length of time required for operations of sounding and dredging in it," wrote Moseley.
Managing the collection of ocean species was the duty of Murray, the voyage's junior naturalist. His chief tool for collecting from the deep was a regular beam trawl, the sort typically used by fishermen. It consisted of a 15-foot piece of wood attached to one side of the opening to a 30-foot- (9-m-) long net bag. The other half of the bag's mouth was weighted to stay open as it drifted along the bottom.
"It used to take us all day to dredge or trawl in any considerable depth, and the net usually was got in only at nightfall, which was a serious inconvenience, since we could not then, in the absence of daylight, make with success the necessary examinations of the structure of perishable animals," Moseley wrote.
Between Brazil and Tristan da Cunha, those necessary examinations included yet more new species of fish pulled from 1,900 fathoms (11,400 feet). The long, thin fish, named Ipnops murrayi, had a paddle-shaped snout and a protruding lower jaw, but most surprising to Murray were the eyes.
"Externally they appear as a continuous flat cornea-like organ, longitudinally divided into two halves, which covers the whole of the upper surface of the snout and partly overlies the bone," Murray wrote. "The function of the organ is difficult to determine. It seems at present probable that it is an organ of modified vision."
A few months later, in late December 1873, the naturalists had one of their most rewarding days of the voyage. Dredging near Marion Island in the southern Indian Ocean, "between one and two hundred animals, belonging to nearly all the marine groups, were taken at each of the hauls, and with a few exceptions they belonged to genera and species discovered for the first time by the expedition," Murray wrote. Seven new genera, including some 35 new species, were found at 1,375 fathoms (8,250 feet), and 29 new species from nine new genera were collected from 1,600 fathoms (9,600 feet).
While the scientific staff managed the dredging, the ship's officers tended to the equally time-consuming task of taking soundings, temperature measurements and water samples. A drop to 2,500 fathoms (15,000 feet) would take the sounding weight more than 30 minutes, and winding that line back in with the 18-horsepower donkey engine would take much longer. Meanwhile, the ship rolled about, held steady in one spot by the coal-fired steam engine.
Curiously, as the Challenger crossed the Atlantic toward Brazil, the officers noticed a distinctive change in sea water temperature between two sets of stations. On the first part of the crossing, deep-sea temperatures were 36 degrees Fahrenheit (2 degrees Celsius), while on the latter part, past St. Paul's Rocks, temperatures at the same depths were 2 degrees F colder. For the time being, Nares could only speculate what this dramatic difference meant. It could be ocean circulation, as Carpenter said, or it could be something else that was keeping the water from mixing, say, the effect of a ridge of undersea mountains running between Africa and South America. Nares offered the latter in his report to the Navy's hydrographer, though he could not explain why the difference disappeared farther south, as they again crossed to South Africa.
For three months, the Challenger dredged and measured across the southern Indian Ocean, until reaching Australia for a two-month respite. Soon enough, she departed to explore the Pacific, where she'd spend most of the next year.
By March 1875, the Challenger found herself between New Guinea and Japan near the Admiralty Islands. Two dredges off the southernmost tip of Mindanao produced an exceptional haul, 22 species of teleostean fish (fish with ossified skeletons) and more than 150 mostly new species of invertebrates, including crinoids. The scientists apparently took great pleasure in giving the new creatures such names as Metacrinus moseleyi, Metacrinus murrayi, and Myzostoma wyville-thomsoni.
Two weeks later, on March 23, the ship's officers sunk a sounding lead into the abyss between the Caroline Islands and the Marianas. The lead went down slowly, and they were sure that the sounding of 4,475 fathoms (26,850 feet) was incorrect. On a second try, they added more weight, but the lead took nearly as long to reach bottom. Two thermometers were sent to collect temperatures, but both broke from the pressure, as if to underscore what the officers were looking down into.
Unwittingly, they had found the "Challenger Deep," a section of the Marianas Trench, the deepest portion of the Pacific to be discovered at the time, and very close to where the present-day record depth of about seven miles was recorded. Here the bottom ooze was reddish-brown with tiny, silica-rich skeletons of radiolarians and speckled with pumice from Pacific volcanoes, instead of the calcium-rich pale gray ooze found elsewhere around the world.
She had nearly half an ocean to cross to reach the Straits of Magellan to complete the around-the-world voyage and return to England. Through the fall and winter, she sailed through the Sandwich Islands (now known as Hawaii), Tahiti, Chile, and around the tip of South America to the Falklands. On April 3, 1876, she set sail from Ascension Island toward home, with one final discovery to make. While crossing from South America to Cape Verde, her crew sounded an unusually shallow bottom in the middle of the Atlantic Ocean. Remembering the variation in temperature observed three years earlier, they deduced that they had found the predicted ridge.
"From the temperature and from the nature of the animals procured by the dredge, there could be little doubt that we had slipped off the ridge on its western side, and that the sounding was in the southern section of the western trough of the Atlantic," Thomson wrote.
Soundings confirmed that the next day. "ItÉappears, both from this and from the remarkable change in bottom temperature, that we had crossed the ridge, and that our soundings on [April 7, 1876] was in the eastern basin of the Atlantic, where all experience led us to expect a considerably higher temperature than in the southwestern." That evening, they crossed the equator for the sixth and final time.
"The objectives of the expedition have been fully and faithfully carried out," Thomson wrote. The expedition was nearly, finally, over.
The Challenger landed in Sheerness on May 24, 1876, Queen Victoria's 51st birthday. Now, the freshly knighted Sir Wyville Thomson could begin work on the second half of the project: The biological and chemical collection had to be studied and the results published. This would end up being as monumental a task as the expedition itself.
"After the contents of the ship had been finally cleared out at Sheerness, we found, on mustering our stores, that they consisted of 563 cases, containing 2,270 large glass jars with specimens in spirit of wine, 1,749 small stoppered bottles, 1,860 glass tubes, and 176 tin cases, all with specimens in spirit; 180 tin cases with dried specimens; and 22 casks with specimens in brine," wrote Thomson.
In addition to the treasure trove of samples, Challenger accomplished her objectives handily, including establishing three major findings. From sampling bottom compositions, the scientists determined that the tiny single-celled organisms foraminifera (heterotrophs that grow calcium-rich skeletons), radiolarians (heterotrophs that grow silicon skeletons), and diatoms (autotrophs that grow silicon skeletons) are distributed around the world in the top-most layers to the ocean, sinking to the bottom when they die to create the respective oozes. They found evidence of ample life on the ocean floor. While they determined low biodiversity in the ooze, better dredging techniques in the 20th century would demonstrate the oceans' floors have a large number of different species also. And they charted the deep basins of the ocean, almost exclusively by temperature. Many decades later, the ridges that isolate those basins were discovered with more sophisticated technologies.
Back at the University of Edinburgh, Thomson divided up specimens and dispatched them to the best scientists of the day, more than 100 in Germany, France, Belgium, Scandinavia, the United States and the United Kingdom. Thomson estimated the ensuing report would include 14 volumes. By 1895, almost 20 years after the Challenger expedition, when the final two volumes were published, the official report was more than 29,552 pages, 50 volumes "each as large as a family bible." More than 18,600 of those pages were devoted to descriptions of the creatures collected.
Unfortunately, Thomson never saw the completed report. He died in 1882, apparently worn down by the stress of battling the British bureaucracy over the politics of the report. Murray stepped in to see the project to completion, and in this golden age of science, he reaped most of the fruits of scientific success that Thomson planted. He published and spoke widely about the expedition and the new science it created.
Smarting from the £200,000 cost (well over £10,000,000 [U.S.$15.6 million] today) for the voyage and publication of the report, the British government didn't launch a major oceanographic expedition for another 50 years. However, the United States, Germany, France, Monaco, Italy, Sweden, and Norway all funded expeditions to follow in the Challenger's wake and build on her successes.
The HMS Challenger struck out on its own to methodically measure the ocean and its inhabitants. Yet for each question she answered, others were raised. To the generations of scientists who followed Thomson, Murray and Moseley, her greatest achievement may be that she showed us how to answer them.
The Voyage of the HMS Challenger: Why You Haven't Heard of It , And Why You Should
While covering the maiden flight of the space shuttle Challenger in 1983, a British journalist reported that the craft was named after a historic U.S. research ship from the 1870s. "I was incensed," says Anthony Rice, marine biologist and author of "Voyages of Discovery: Three Centuries of Natural History Exploration."
But if its team of scientists created the science of oceanography, why isn't the British vessel HMS Challenger better known?
"Possibly because ocean science is not considered as sexy as other fields of human endeavor; possibly because none of the Challenger scientists was a Bob Ballard; and possibly because there was no obvious single objective like the South Pole, mountain top, or Titanic for the public to identify with," Rice says.
While Darwin's "Voyage of the Beagle" was a best-selling popular travel book in England, the "Challenger Report" was a sternly scientific publication that fulfilled a scientific mission. "The way to look at the voyage is its mind-numbingly boring acquisition of data," Rice says. "That's how a science is born."
That's why, even if general audiences aren't familiar with the expedition, the 50-volume report is still suggested reading among oceanography students.
"Understanding the ocean on a large scale is how it's being studied now," says Jeff Levinton, a professor of marine biology at the State University of New York at Stony Brook and author of "Marine Biology: Function, Biodiversity, and Ecology." "The essence of open-ocean science is collaboration among disciplines."
"The zoological results in many ways are as relevant today as they were then, they are brilliant, absolutely perfect," Rice says. The physical results, on the other hand, aren't quite as precise.
"As techniques improved, their results became less and less valuable, until today it has no value at all, other than as a curiosity," Rice says. With thermometers that were accurate only to one-tenth of a degree, that's at least an order of magnitude less accurate than modern thermometers.
Nonetheless, the Challenger data may serve one final role, as a baseline for comparison against possible ocean temperature rise from global climate change. If that's the case, the Challenger will have given us one more in a long list of contributions to remember her by.