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Making the deep sea visible

the Challenger Report

Illustration of naturalists conducting research on board

Challenger played an essential physical role in retrieving data and specimens from the world’s oceans, but also as an intellectual space for scientific deliberation, testing and writing, and the process of publication.

Although scientific staff published their preliminary results during the voyage, at the heart of the publishing project was the Challenger Office in Edinburgh which coordinated the movement of specimens, images, and text with collaborators around the globe.

Transferring the scientific work from sea to land, Thomson had the Challenger collection of over 100,000 specimens moved to 32 Queen Street in New Town. In a time when individuals and nations competed for the prestige of scientific discovery and the control of maritime and government resources, Thomson used this space to foster a network of marine zoologists from Europe and America.

It would take the dedicated work of specialists to categorise, select, name, and describe new species and prepare reports for publication. But before specimens could be distributed, the collection had to be catalogued and prepared for travel.

To help with sorting the collection, Thomson called upon his colleagues in the international scientific community who travelled to Edinburgh to observe and discuss what specimens, data, and materials had been discovered.

Plan & elevation of the new town of Edinburgh

Creator Robert Kirkwood
Date 1819
Object reference NLS Signet.s.088
Credit / Usage information Image courtesy of National Library of Scotland (CC-BY-NC-SA Signet)

Many of the leading figures of zoology, comparative anatomy and natural selection became involved with the work of the Challenger collections during this time, including Alexander Agassiz, Ernst Haeckel, Thomas Henry Huxley and Ray Lankester.

Title: Plan & elevation of the new town of Edinburgh
Creator Robert Kirkwood
Date 1819
Object reference NLS Signet.s.088
Credit / Usage information Image courtesy of National Library of Scotland (CC-BY-NC-SA Signet)

Historians and scientists consider the 50 volumes that make up the Report on the Scientific Results of the Voyage of HMS Challenger During the years 1872-76as the intellectual foundation of oceanography. This series included 30,000 pages of letterpress, 3,000 lithographic plates, 200 maps, and numerous woodcuts. Hundreds of people, including sailors, artists, illustrators, printers, editors, naturalists, analysts, chemists, and many more, contributed to and shaped the reports’ construction.

With the publication of the final volume in 1895, the report presented a compendium of what was known of the oceans at the end of the 19th century, contributing to a baseline for how we measure the effects of climate change on our oceans today.

One of the most significant volumes of the series is the Report on the deep-sea deposits based on the specimens collected during the voyage of HMS Challenger in the years 1872 to 1876 which transformed the study and scientific understanding of the geology of the ocean floor. This chart, which appears in the report, was the first to show global distribution of deep-sea sediments.

Chart showing the composition of the ocean floor

Creator John Murray
Date 1891
Place of creation London, England

Collecting and assembling knowledge of the ocean in large, expensive publications was not only a scientific exercise. Knowledge of the ocean was integral to Britain’s maritime trade network and imperial expansion. The results of the scientific project also enabled the movement of navies, people, information, and goods.

Title: Chart showing the composition of the ocean floor
Creator John Murray
Date 1891
Place of creation London, England
Creator Alphonse Francois Renard
Date 1891
Place of creation London, England
Object reference S.B. F. 5083 Cha.
From Report on the deep-sea deposits based on the specimens collected during the voyage of HMS Challenger in the years 1872 to 1876

Understanding and illustrating the ocean floor

While most of the volumes of the Challenger Report were dedicated to marine zoology, reports on the physical and chemical aspects of the ocean added vital strands to the development of ocean science. Over a period of ten years, John Murray and Belgian geologist Alphonse Renard (1842-1903), co-authors of the Report on Deep-Sea Deposits, carried out an extensive analysis of the rocks and sediments that the expedition had dredged and sounded from the ocean floor.

In a radical change to how we study and illustrate the composition of geologic materials, the report introduced for the first time the techniques of microscopic petrography to the study of ocean sediments. This new method of geologic analysis developed in the 1860s and 1870s, in which thin slices of rock were viewed under powerful microscopes, could determine the history and composition of ocean sediments.

Using this technique and others, the Report on Deep-Sea Deposits explained the origin of red clay found at great depths, analysed the composition of manganese nodules, and discovered extra-terrestrial materials in deep-sea sediments.

Click the images below to discover more about these techniques.

  • Shown in polarised light, this chromolithograph shows a magnified specimen of manganese nodules from the South Pacific. During the voyage, the dredge brought up several of these black rocks, ranging in size from small marbles to large potatoes. How nodules formed on the ocean floor was strongly debated.

    Studying some of these nodules under a microscope, Murray noticed small spherules made of iron but could not account for their origin. On the recommendation of his former teacher, Archibald Geikie (1835-1924), then Professor of Geology and Mineralogy at the University, Murray used microscopic petrography to study their structure.

    With this new method, Murray confirmed the presence of ‘cosmic dust’ in ocean sediments: material that had come to the earth as meteorites. This significant finding offered clues to how iron – an essential element to living organisms – became available to animals living in the deep sea.

    Title: Plate XVIII of cosmic spherules in deep sea deposits
    Creator John Murray
    Creator Alphonse Francois Renard
    Creator Eyre & Spottiswoode (printer)
    Date 1891
    Place of creation London, England
    Object reference S.B. F. 5083 Cha.
    From Report on the deep-sea deposits based on the specimens collected during the voyage of HMS Challenger in the years 1872 to 1876

  • Microscopic petrography was a highly specialised field, and in the early 1870s it was not commonly practised in Britain. The study of geology was transformed in 1873 when the German physicist Ernst Abbe (1840-1905) discovered the optical formula necessary for a lens to produce a sharp image free from distortion. Using powerful microscopes, geologists in Germany, France and Belgium viewed thin sections of rocks illuminated by polarized light. As if by magic, the internal crystalline structure of igneous rocks became visible as never before.

    The new way of seeing and understanding the composition of rocks was soon accompanied by new ways of designing and printing scientific images. This type of study and illustration was beyond Murray’s expertise. It was during this great change in geology that Renard, then Professor at the Jesuit College in Louvain, visited the Challenger Office in Edinburgh in 1877. Unlike Murray, Renard was one of the few experts of the new technique.

    Intrigued by the possibility of applying microscopic petrography to better understand ocean processes and geologic formations, a type of study that had not yet been attempted, Renard accepted a formal invitation from Thomson to apply his analytical and illustrative techniques to the study of Challenger deep-sea deposits.

    Title: Plate XVII of manganese nodules in deep sea deposits
    Creator John Murray
    Creator Alphonse Francois Renard
    Creator Eyre & Spottiswoode (printer)
    Date 1891
    Place of creation London, England
    Object reference S.B. F. 5083 Cha.
    From Report on the deep-sea deposits based on the specimens collected during the voyage of HMS Challenger in the years 1872 to 1876

  • Producing illustrations for the Report on Deep-Sea Deposits involved many people and could not all be done in Edinburgh. Through Murray and Renard’s network, microscopic petrographers, lithographers, and specialist printers in Brussels, Vienna, and Edinburgh were enlisted to produce the report’s images. This chromolithograph plate of cosmic spherules in deep-sea deposits was printed at the Austrian Imperial and State Printing House, Vienna.

    Chromolithography was an expensive and exacting method of printing that required specialist equipment and highly skilled workers. Dr J. Heitzmann, who is credited on this plate, worked with petrographers in Vienna, where he mapped and etched these detailed images of specimens onto stones. The stone plates were then sent to the Viennese Imperial and State Printing House.

    To make the report’s richly illustrated images, the lithographer drew onto the surface of a stone plate using oil, fat, or wax and then treated it with a mixture of acid and gum arabic to raise the image from the stone. Each stone was used to print a single colour. The printer moistened these plates with water, applied an oil-based ink with a roller, and then pressed the plate onto a sheet of thick paper.

    The application of ten separate plates was not unusual for a multi-coloured image like this one. To avoid a blurred image, each of the plates had to be exactly aligned to reference points placed on the paper. As a result of this meticulous work, this plate carries subtle graduations in tone.

    Each of the 29 plates manufactured for the Report on Deep-Sea Deposits followed a similar process in Brussels, Vienna, or Edinburgh.

    Title: Plate XXIII of deep sea deposits
    Creator John Murray
    Creator Alphonse Francois Renard
    Creator Dr J. Heitzmann (lithographer)
    Place of creation Vienna, Austria
    Creator Eyre & Spottiswoode (printer)
    Date 1891
    Place of creation London, England
    Object reference S.B. F. 5083 Cha.
    From Report on the deep-sea deposits based on the specimens collected during the voyage of HMS Challenger in the years 1872 to 1876

In the Report on Deep-Sea Deposits Murray and Renard also added new features to existing illustration techniques. Putting thin sections of deep-sea deposits under the microscope revealed the shells of a range of foraminifera, single-celled organisms about the size of a grain of sand. This printed tissue overlay outlined and labelled different species, helping readers to better identify these small fossils in the rock.

Challenger collected foraminifera both as live specimens from tow nets and as fossils found in deep-sea dredgings. These tiny organisms are integral to balancing the carbon cycle, building their shells from calcium carbonate. When they die, they sink, bringing carbon down to the ocean floor which helps neutralize acidity.

Foraminifera are sentinels of climate change. Comparing specimens collected in the 21st century to those collected by Challenger, reveals they have significantly thinner shells. Increased carbon in the atmosphere has increased ocean acidity, conditions which make it difficult for shell building. With thinner shells less carbon is locked in the oceans when they die and sink to the floor. This negative feedback loop leaves more carbon in the air, which, in turn, increases ocean acidity.

Plate XII of foraminifera with a printed tissue overlay

Creator John Murray
Date 1891

Title: Plate XII of foraminifera with a printed tissue overlay
Creator John Murray
Date 1891
Creator Alphonse Francois Renard
Creator Eyre & Spottiswoode (printer)
Place of creation London, England
Object reference S.B. F. 5083 Cha.
From Report on the deep-sea deposits based on the specimens collected during the voyage of HMS Challenger in the years 1872 to 1876