'Core on Deck!'
Research vessel is providing a unique look at the Earth's geologic evolution
By Dave Field

The scientific drillship JOIDES Resolution is currently drilling and completing experiments in the Australian region as part of the Ocean Drilling Program (ODP) - operations sponsored by the Joint Oceanographic Institutions for Deep Earth Sampling (JOIDES). The drillship is quite unique and, in recognition of the history of ocean exploration, the latter part of her name 'Resolution' is a tribute to another famous ship, Captain Cook's HMS Resolution.
    The technical aspects of drilling into a target which is several kilometres away from the top drive drilling machine provide quite a challenge, devilishly complicated by elemental forces which attempt to move the ship both horizontally and vertically. The designers of JOIDES Resolution built her to address these problems.
    Since usually the sea is too deep to allow the ship to anchor, a dynamic positioning process is used. The ship locates over the prospective borehole using twelve thrusters which compensate for the forces of ocean currents, waves, and winds. The thrusters are manipulated by a sophisticated computer system which analyses information relating to an acoustic transponder placed on the seafloor after arriving on site. Three sensors on the ship's hull interact with the transponder, providing vectoring information and, in practice, the ship neutralizes the greatest push off position with her two main screws while other thrusters manage the lesser displacing forces. The system allows the ship to maintain a horizontal position to within 2% of the depth of the water in which she is operating. JOIDES Resolution carries 9,000m of drill pipe and can drill in water 6 kilometres deep.
    Wave action creates problems of vertical location, and movement in this plane is accommodated by the largest heave compensator in the world, with a 364,000 kilo capacity. It ensures that drilling will be sustained until the ship is experiencing waves greater than 4 metres.
    JOIDES Resolution has an impressive record. She's taken cores working through as much as 6,200m of water, and can boast a deepest seafloor penetration of 2,200m.
    Different seafloor compositions require different drilling techniques, and these are continuously under development. When considering the variations, bear in mind that the integrity of the core sample is all-important. The structure of soft sediment would be destroyed by a rotating drill, and when penetrating soft substrate a hydraulic piston corer is driven through the drill bit and ahead into the substrate, using water pressure. When drilling is taking place through substrate which is sometimes hard and sometimes soft, an extended core barrel pushes ahead of the drill bit in soft sediment, but retracts inside the drill bit when harder material is encountered.
    It's now possible to drill in bare rock - previously rock drilling was only possible when the rock was covered by 50 to a 100 metres of soft sediment. The reason was that the sediment layer stabilized the drill-string during the first stages. No sediment, no drilling. One of the methods employed uses a cement-filled guide base weighing 18,000 kilos. This guide base is sent to the sea floor to stabilize the drill string. Depending on the specific objective and to save time, specially-designed drilling motors rotate the bit while the main drill-string remains stationary. This reduces vibration and fatigue problems that could wreak havoc when coring in young rock which isn't covered by sediment.
    A third drilling system was evaluated recently. ODP drilled large-diameter casing into hard fractured rock on the sea floor. In the process (described as water hammer drilling), a percussion drill operating in a similar way to a jack hammer, though powered by liquid rather than air, creates a 375 mm borehole. It's followed by a 340 mm casing which is driven into the borehole with the intention of stabilizing the borehole as it's drilled. Trials on JOIDES Resolution were most encouraging and the drilling system will be developed further. This is a good place to mention ODP's style - always pushing the 'envelope'.
    JOIDES Resolution started her life as an oil exploration ship. Christened Sedco/BP, she was modified into her scientific role in 1984 and renamed in 1996. An unusual sight, the ship is 21m wide and 143m long, her drilling rig rising to 61.5m above the waterline. Any discussion of the ship leads towards big numbers. If she's working in 5,500m of water it will take around 12 hours to lower pipe to the sea bed. A pipe section weighs around 874 kilos and is approximately 28m long. The heavy action takes place on the drilling deck, where drill pipe is manoeuvred through a 7m square opening in the ship's hull called the 'moon pool'.
    Any scientist will tell you that its hard, demanding and dirty work collecting samples, and that quality sample collecting is the cornerstone of any investigation. Yet how well you analyse those samples will also make quite a difference. JOIDES Resolution has an astonishing array of laboratories for core analysis. This facility attracts sediment geologists, palaeontologists, geochemists, geophysicists, and petrologists world-wide.
    No less than twelve laboratories spread through seven levels of the ship, and scientific staff run twelve hour shifts continuously as cores are recovered. The routine is that, when a core becomes available (an event heralded by the cry 'Core on deck!'), its length is measured in the core reception area, then it is sectioned for study and storage, the top and bottom of each section is colour-coded, and the core liner is identified with the seafloor location from which it was recovered. Paleontology staff examine fossils from the base of the core to determine the age of the lowest (therefore most likely the oldest) component. A chemist examines for signs of hydrocarbon presence - gas pockets, frothing inside the liner, and bubbles. Drilling into hydrocarbon deposits is potentially dangerous and, if hydrocarbons are detected, the drilling is terminated.
    The next step is a trip to the Physical Properties Laboratory where density, strength and thermal conductivity are measured. Paleomagnetics comes next and the core gives up its information on the earth's magnetic field changes. At this stage its time to split the core lengthways, and immediately one half is archived. From then on samples of the other half are removed and sent to the appropriate laboratories depending on the ODP sampling plan. The opportunities for leading-edge science on JOIDES Resolution are incredible. There are thin section, X-ray, chemistry, paleontology, and microscopy facilities. There's a science lounge, computer user room and computer centre. An electronics shop and photography lab. At another level on the ship there's refrigerated core storage and the 'second look lab'.
    The underway geophysics lab is under the helipad at the stern of the ship, and it delivers information on ship's position, water depth, and magnetic data associated with subocean floor geology. As this wealth of information is gleaned it is stored in the ship's computer network and becomes available to scientists working anywhere on the ship.
    The very wide spread of skills required and the 24-hour operations routine means the ship must carry around 25 scientists, 30 engineers and technicians, with 47 crew members and a catering staff of 14 cooks and stewards to keep up with the workload. The calibre of the people, their enthusiasm and the quality of the ship's laboratories has allowed the Ocean Drilling Program to markedly advance our knowledge of the Earth in many areas:
    Cores taken by the ship clearly show that variation in the Earth's tilt and orbit, with other astronomical changes, have modified ecosystems, rainfall levels and ocean currents.
    Geologists at one time believed that the Earth entered the Ice Age simply as a consequence of the continued extension of the Polar Front. Now, there's an entirely new view of how we entered the Ice Age. Cores taken from the Norwegian Sea indicate that, some 2.8 to 2.9 million years ago, the Norwegian current rapidly cooled, while similar work in Baffin Bay showed cooling around 2.5 million years ago. These findings where supported by investigations on sediment samples collected off the West African coast. The West African work pointed to a dramatic increase in coastal upwelling between 2.5 and 3 million years ago. Coupled with older information from Antarctica, these indications of virtually simultaneous changes will significantly enhance our understanding of the processes which will lead into the next glacial period.
    Theories of inundation are also being confirmed or modified. Cores collected in coral atolls and continental margins illustrate a long history of sea-level change by providing a record of sedimentation deposition over time. For example, periods of low sea level correspond to times of slow carbonate deposition in the basins surrounding the Bahama Banks. When the banks were flooded during high sea levels, high carbonate sedimentation occurred. At coastal sites where material carried in coastal runoff is the major material contributing to sedimentation, a converse carbonate deposition process takes place. The possibility of sea-level change is of increasing concern as it becomes more evident that even a small change in sea level is likely to have a profound effect.
    There are also studies on active hydrothermal systems which may translate into more effective land-based mineral exploration. The ship has drilled seafloor through which superheated water loaded with dissolved minerals is rising. When the hot water meets the extremely cold oceanic seawater, the minerals precipitate, often resulting in elaborate mineral arrangements rearing many metres up from the seafloor.
    During Leg 179 (each of the ship's two-month expeditions is called a 'Leg'), which ran from April 21st until June 7th, a borehole was drilled in the Indian Ocean and fitted with casing and a reentry cone. The ship will revisit the borehole, and a Geophysical Ocean Bottom Observatory (GOBO) will be installed, extending the Earth's seismologic network. As evidenced by the recent tragedy in Papua New Guinea when thousands of people were lost due to a tsunami, volcanic and earthquake investigations are most important. The earth's oceans have to date received only cursory observation, unlike most continents where there's adequate earthquake monitoring equipment.
    ODP's Leg 180 began when the drillship departed Australia on June 13th to drill in the sea off Papua New Guinea for two months. In that area active faults are rifting the eastern side of Papua New Guinea apart and causing sea floor spreading - a new ocean is forming.
    The Ocean Drilling Program has resulted in JOIDES Resolution taking cores in every sea on the earth, and cores from the ship's expeditions are stored at four repositories around the world. Truly an international operation, while over 60% of ODP's cost (US$48 million each year) is provided by the United States, funds also come from other countries, and there are twenty-one other partner nations.

About the Author:
Dave Field is a freelance writer stationed in Australia where he covers a range of scientific and human interest topics. He may be reached at (08) 8945-0243.

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