Challenger Expedition (1872–1876)

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.

Scientific objectives

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.

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.