Ocean Drilling Program

Ocean Drilling Program The Ocean Drilling Program (ODP) is an international partnership of scientists and research institutions organized to explore the structure and history of the Earth beneath the ocean basins. Its infrastructure cost of some $45 million per annum is funded by the US National Science Foundation together with contributions from 20 non-US partner countries. The scientific operations are carried out from Texas A&M University in the USA. The overall planning and programme advice is provided by the Joint Oceanographic Institutions for Deep Earth Sampling (JOIDES), an international group of institutes and universities. The JOIDES structure incorporates a series of managerial, scientific, and technical panels staffed by representatives of the contributing countries. The legacy of ODP includes hundreds of kilometres of drill core, the JANUS database containing many gigabytes of electronically stored shipboard measurements, and thousands of scientific and technical articles in its own volumes (Proceedings of the Ocean Drilling Program) and in the outside literature. The unused core is currently stored in purpose-built repositories in the US and Germany.

ODP is the latest of several international scientific ocean drilling projects. Their inspiration was the Mohole Project of the early 1960s. This was an ambitious but unfulfilled plan to drill through the oceanic crust of the Eastern Pacific to reach the crust-mantle boundary (the Moho) at one of its most accessible points. It led to the Deep Sea Drilling Project (DSDP), which began in 1968 as a US initiative aimed at the global reconnaissance of the ocean basins. DSDP ran its own drilling ship, the Glomar Challenger, which was purpose-built for the scientific drilling of the deep ocean floor. In 1974, DSDP became an internationally funded programme for what is known as its International Phase of Ocean Drilling (IPOD). DSDP ended in 1983, when the Glomar Challenger reached the end of her capabilities. ODP was set up in 1985 with its new ship, the JOIDES Resolution.

The JOIDES Resolution is a commercial drilling vessel 143 m long, which has been extensively modernized and adapted for scientific drilling. It can drill in water depths in excess of 8000 m and carries over 9000 m of drill pipe on board. It has twelve computer-operated thrusters which enable the ship to maintain position to within 1 m even in heavy seas. A 400-ton heave compensator keeps the drill string stable relative to the sea floor. The feature that sets it apart from commercial drilling vessels is its seven-storey stack of laboratories where scientists can process and analyse each 9.5 m (maximum) length of core and interpret measurements made in situ within the hole. The laboratories contain space for studies of sedimentology, palaeontology, petrology, geochemistry, palaeomagnetism, and physical properties and contain equipment that includes X-ray diffraction, X-ray fluorescence, and a cryogenic magnetometer.

Ocean drilling is organized into ‘Legs’, each of which usually lasts about two-months and comprises a single scientific project. By the time ODP ends in 2003, DSDP and ODP will together have completed more than 200 Legs of drilling. The deepest hole at the time of writing, in Eastern Pacific oceanic crust, exceeds 2 km.

The science carried out by ODP is currently driven by its Long Range Plan entitled Understanding our Dynamic Earth through Ocean Drilling. This plan defines two major scientific themes: dynamics of the Earth's environment and dynamics of the Earth's interior. Within each theme are a series of specific sub-themes within which ocean drilling can make a major contribution. For the dynamics of the Earth's environment, these include: understanding the Earth's changing climate; causes and effects of sea-level change; and sediments, fluids, and bacteria as agents of change. For the dynamics of the Earth's interior, the sub-themes include: transfer of heat and materials to and from the Earth's interior; and investigating deformation of the lithosphere and earthquake processes.

Studies of ODP core have shown that bacteria may live in deep-sea sediments at least a kilometre below the sea floor. The Long Range Plan includes a pilot programme to explore this deep biosphere in more detail. It also includes the developments in drilling and logging technologies and in down-hole experimentation that are needed to achieve its scientific objectives. Some of these developments may lead to the longer-term goals of deep penetration of the ocean crust and continental margins and the creation of sea-floor observatories.

The scientific achievements of the Ocean Drilling Program are too many to list here. They have led to the continuing refinement of our understanding of global tectonics, mantle dynamics, global element fluxes, ocean history, glacial history, sea-level change, climate change, global hazards, and the Earth's resources. Examples of more recent ‘high-profile’ ODP Legs include: Leg 164, which drilled a deposit of gas hydrate, a potential new fossil fuel resource; Legs 165 and 171B, which drilled the K–T (Cretaceous—Tertiary) boundary, with its evidence for the global consequences of a large meteorite impact; Legs 158 and 169, which drilled actively forming massive sulphide deposits and provided new insights into the process of ore genesis; and Leg 169S, which drilled finely laminated sediments containing the best record so far of past global climate changes.

The scope for scientific discovery by ocean drilling has evolved with time. The greatest achievement of DSDP was probably the ‘ground-truthing’ of the plate-tectonic hypothesis by providing key information on the age of the ocean basins and the processes that take place at plate boundaries. By contrast, the greatest achievement of ODP so far is probably the development of an astronomically tuned geological timescale, which now provides the most reliable absolute method of dating yet available for the Neogene (23.3–1.64 Ma). This has been achieved by matching the cyclic variations in physical and chemical properties down ODP core to the quasi-cyclic variations in Earth—Sun orbital geometry known as Milankovich cycles. This timescale has formed the foundation of many other achievements of ODP, such as the construction of ultra-high-resolution climate records from the Earth's past.

Julian A. Pearce

Bibliography

25 Years of Ocean Drilling. Oceanus 36, 1993. Woods Hole Oceanographic Institution, Wood's Hole, Mass.