The Challenger expedition of 1872–1876 was a scientific programme that made many discoveries to lay the foundation of oceanography. The expedition was named after the naval vessel that undertook the trip, HMS Challenger.
The expedition, initiated by William Benjamin Carpenter, was placed under the scientific supervision of Sir Charles Wyville Thomson—of the University of Edinburgh and Merchiston Castle School—assisted by five other scientists, including Sir John Murray, a secretary-artist and a photographer. The Royal Society of London obtained the use of Challenger from the Royal Navy and in 1872 modified the ship for scientific tasks at Sheerness, equipping it with separate laboratories for natural history and chemistry. The expedition, led by Captain George Nares, sailed from Portsmouth, England, on 21 December 1872. Other naval officers included Commander John Maclear.
Under the scientific supervision of Thomson himself, the ship travelled approximately 68,890 nautical miles (79,280 miles; 127,580 kilometres) surveying and exploring. The result was the Report of the Scientific Results of the Exploring Voyage of H.M.S. Challenger during the years 1873–76 which, among many other discoveries, catalogued over 4,000 previously unknown species. John Murray, who supervised the publication, described the report as "the greatest advance in the knowledge of our planet since the celebrated discoveries of the fifteenth and sixteenth centuries". Challenger sailed close to Antarctica, but not within sight of it. However, it was the first scientific expedition to take pictures of icebergs.
The expedition, which circumnavigated the Earth, collected data by lowering sounding lines to the bottom of the ocean floor to measure its depth and collect sediment samples, by collecting marine organisms by means of dredges lowered to the ocean floor and trawls lowered into the water at different depths, by measuring temperature at various depths and by collecting samples of seawater at standard depths for chemical analysis. They collected plankton samples and recorded the speed and direction of ocean surface currents. Samples were preserved in brine or alcohol, or dried, then brought to Europe and distributed to various experts to analyse.
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Preparations
To enable it to probe the depths, 15 of Challenger's 17 guns were removed and its spars reduced to make more space available. Laboratories, extra cabins and a special dredging platform were installed. Challenger used mainly sail power during the expedition; the steam engine was used only for dragging the dredge, station-keeping while taking soundings, and entering and leaving ports. It was loaded with specimen jars, filled with alcohol for preservation of samples, microscopes and chemical apparatus, trawls and dredges, thermometers, barometers, water sampling bottles, sounding leads, devices to collect sediment from the sea bed and great lengths of rope with which to suspend the equipment into the ocean depths.
Because of the novelty of the expedition, some of the equipment was invented or specially modified for the occasion. It carried 181 miles (291 km) of Italian hemp rope for sounding.
Expedition
On its landmark journey circumnavigating the globe, 492 deep sea soundings, 133 bottom dredges, 151 open water trawls and 263 serial water temperature observations were taken. About 4,700 new species of marine life were discovered.
The scientific work was conducted by Wyville Thomson, John Murray, John Young Buchanan, Henry Nottidge Moseley and Rudolf von Willemoes-Suhm. Frank Evers Bed was appointed prosector. The official expedition artist was John James Wild. As well as Nares and Maclear, others that were part of the naval crew included Pelham Aldrich, George Granville Campbell and Andrew Francis Balfour (one of the sons of Scottish botanist John Hutton Balfour). Also among the officers was Thomas Henry Tizard, who had carried out important hydrographic observations on previous voyages. Though he was not among the civilian scientific staff, Tizard would later help write the official account of the expedition, and also become a Fellow of the Royal Society.
The original ship's complement included 21 officers and around 216 crew members. By the end of the voyage, this had been reduced to 144 due to deaths, desertions, personnel being left ashore due to illness, and planned departures.
Challenger reached Hong Kong in December 1874, at which point Nares and Aldrich left the ship to take part in the British Arctic Expedition. The new captain was Frank Tourle Thomson. The second-in-command, and the most senior officer present throughout the entire expedition, was Commander John Maclear. Willemoes-Suhm died and was buried at sea on the voyage to Tahiti. Lords Campbell and Balfour left the ship in Valparaíso, Chile, after being promoted.
The first leg of the expedition took the ship from Portsmouth (December 1872) south to Lisbon (January 1873) and then on to Gibraltar. The next stops were Madeira and the Canary Islands (both February 1873). The period from February to July 1873 was spent crossing the Atlantic westwards from the Canary Islands to the Virgin Islands, then heading north to the North Atlantic archipelago and Imperial fortress colony of Bermuda (home base of the North America and West Indies Station), east to the Azores, back to Madeira, and then south to the Cape Verde Islands. During this period, there was a detour in April and May 1873, sailing from Bermuda north to Halifax and back, crossing the Gulf Stream twice with the reverse journey crossing further to the east.
Scientific objectives
The Royal Society stated the voyage's scientific goals were:
To investigate the physical conditions of the deep sea in the great ocean basins—as far as the neighborhood of the Great Southern Ice Barrier—in regard to depth, temperature, circulation, specific gravity and penetration of light.
To determine the chemical composition of seawater at various depths from the surface to the bottom, the organic matter in solution and the particles in suspension.
To ascertain the physical and chemical character of deep-sea deposits and the sources of these deposits.
To investigate the distribution of organic life at different depths and on the deep seafloor.
One of the goals of the physical measurements for HMS Challenger was to be able to verify the hypothesis put forward by Carpenter on the link between temperature mapping and global ocean circulation in order to provide some answers on the phenomena involved in the major oceanic mixing. This study is a continuation of the preliminary exploratory missions of HMS Lightning and HMS Porcupine. These results are important for Carpenter because his explanation differed from that of another renowned oceanographer at the time, the American Matthew Fontaine Maury. All these results of physical measurements were synthesized by John James Wild (i.e. the expedition's secretary-artist) in his doctoral thesis at the University of Zurich.
A second important issue concerning the collection of different kinds of physical data on the ocean floor was the laying of submarine telegraph cables. Many transoceanic cables were being laid in the 1860s and 1870s and their efficient laying and operation were matters of great strategic and commercial importance.
At each of the 360 stations the crew measured the bottom depth and temperature at different depths, observed weather and surface ocean conditions, and collected seafloor, water and biota samples. Challenger's crew used methods that were developed in prior small-scale expeditions to make observations. To measure depth, they would lower a line with a weight attached to it until it reached the sea floor. The line was marked in 25-fathom (150 ft; 46 m) intervals with flags denoting depth. Because of this, the depth measurements from Challenger were, at best, accurate to the nearest 25-fathom (150 ft; 46 m) demarcation. The sinker often had a small container attached to it that would allow for the collection of bottom sediment samples.
Challenger Deep
On 23 March 1875, at sample station number 225 located in the southwest Pacific Ocean between Guam and Palau, the crew recorded a sounding of 4,475 fathoms (26,850 ft; 8,184 m), which was confirmed by a second sounding. As shown by later expeditions using modern equipment, this area represents the southern end of the Mariana Trench and is one of the deepest known places on the ocean floor.
Modern soundings to 6,012 fathoms (36,070 ft; 10,994 m) have since been found near the site of Challenger's original sounding. Challenger's discovery of this depth was a key finding of the expedition in broadening oceanographic knowledge about the ocean's depth and extent; the depression, the Challenger Deep, now bears the name of the vessel and its successor, HMS Challenger II, which in 1951 identified a depth of 5,944 fathoms nearby. Thomas Gaskell, the Chief Scientist on HMS Challenger II, observed that the later measurementwas not more than 50 miles from the spot where the nineteenth-century Challenger found her deepest depth [...] and it may be thought fitting that a ship with the name Challenger should put the seal on the work of that great pioneering expedition of oceanography.The expedition also verified the existence of the Mid-Atlantic Ridge extending from the southern hemisphere to the northern one.
Legacy
Findings from the Challenger expedition continued to be published until 1895, 19 years after the completion of its journey, by the Challenger Office, Edinburgh, established for that purpose. The report contained 50 volumes and was over 29,500 pages in length. Specimens brought back by Challenger were distributed to the world's foremost experts for examination, which greatly increased the expenses and time required to finalize the report. The report and specimens were displayed at the British Natural History Museum from January to July, 2023. Some specimens, many of which were the first discovered of their kind, are still examined by scientists today.
A large number of scientists worked on categorizing the material brought back from the expedition including the paleontologist Gabriel Warton Lee. George Albert Boulenger, herpetologist at the Natural History Museum, named a species of lizard, Saproscincus challengeri, after Challenger.
Before the Challenger expedition, oceanography had been mainly speculative. As the first true oceanographic cruise, the Challenger expedition laid the groundwork for an entire academic and research discipline. "Challenger" was applied to such varied phenomena as the Challenger Society for Marine Science, the oceanographic and marine geological survey ship Glomar Challenger and the Space Shuttle Challenger.