How deep are the oceans?

Underwater landscape: The combination of advanced sonar and satellite technology can produce high-resolution 3D models of seascapes like this one in the Caribbean. However, for much of the sea fl oor, there is still insuffi cient data. (Source: http://pubs.usgs.gov/of/2004/1400/). The 7th International Geographic Congress, held at Berlin in 1899, gave the start signal for the mapping of the ocean fl oors. It set up a “commission on sub-oceanic nomenclature”, which was also responsible for the publication of a general bathymetric chart. This commission met in Wiesbaden, Germany, in April 1903, and was chaired by Prince Albert I of Monaco (1848–1922), a pioneer of oceanography and an early advocate of environmental protection. The commission initiated the General Bathymetric Chart of the Oceans (GEBCO) series, as proposed in a memorandum by Julien Thoulet (1843– 1936) from the University of Nancy. Since then progress in bathymetry (depth measurement) of the world’s oceans has been slow, due to the technical and administrative challenges involved in exploring the vast seascapes beyond territorial waters and hidden under several kilometres of water. An initial map of 24 sheets, the Carte générale bathymétrique des oceans was printed in Paris in 1905 and was criticised as inadequate. A second commission convened in Monaco in 1910 to raise the standard. The second set of maps was printed from 1912 to 1931 with contour lines representing the terrestrial relief and a revised nomenclature. By then, the introduction of sonar instruments made data collection considerably easier. After the death of Prince Albert in 1922, the project was transferred to the International Hydrographic Bureau, which was renamed the International Hydrographic Organization (IHO) in 1970. Only parts of the next editions were published until 1972, at which point the UNESCO and the Canadian government reorganised the effort and managed to get a global coverage at a scale of 1:10 million, i.e. 1 cm on the map equals 100 km, in 1982. Since then, the GEBCO project went digital, published a centenary edition of the ocean maps, and established itself as the global repository for ocean fl oor mapping. However, maps of the global sea fl oor are in most parts still less detailed than those we have of the surface of Mars. Technical challenges remain, such as mapping at extreme depth or under sea ice, and the demands for better data increase. From 15–17 June, experts will meet at Monaco for a Forum for Future Ocean Floor Mapping, with the brief to agree on a road map for future bathymetry efforts.