Late next summer, when the Arctic pack ice has receded, three icebreakers will head north from Siberia to escort a drilling ship into the treacherous Arctic Ocean. Cutting through ice floes, the convoy will launch one of the most ambitious ocean-drilling projects ever undertaken, in an attempt to find a missing piece of the puzzle of our planet's climatic past.

Tentatively approved last month, the expedition will be one of the first projects of the new Integrated Ocean Drilling Program (IODP) — a scheme that will unite equipment and expertise from the United States, Japan and a consortium of 15 European nations. The programme aims to drill where no ship has drilled before, from the icy North Pole to deep inside a fault line off the coast of Japan, and to study the life forms they find deep beneath the sea floor along the way.

Illustrious career: the research drilling vessel JOIDES Resolution has sailed the world for more than two decades. Credit: ODP

After a decade of planning, the IODP was officially born on 1 October. It replaces the Ocean Drilling Program (ODP), an enterprise of 20 nations that was phased out in September after nearly 20 years of expeditions. The ODP had only a single ship — the US vessel JOIDES Resolution — which sailed the globe, sinking holes into the ocean bottom and retrieving a huge volume of sediment cores (see 'Core values').

Over two decades, the Resolution's bounty has helped to prove that asteroids such as the one that slammed into Mexico 65 million years ago — thought by some researchers to have caused the dinosaurs' demise — can create clouds of dust that settle all around the world. Sediment cores pulled from the Indian coast helped to put a date on when the Himalayas were born, as they revealed a mass of rock that was weathered by rain as the mountains were pushed up. And researchers have gained clues about Earth's ancient climate — the fossils found in layers of mud laid down on the ocean floor over millennia have revealed the temperature of those waters long ago.

But the Resolution couldn't go everywhere, and never mounted a campaign on the North Pole. In 1996, geologist Jan Backman, of Stockholm University in Sweden, and his colleagues took a lone icebreaker — operated independently of the ODP — and tried to drill a deep core on the Lomonosov Ridge, an undersea mountain ridge that meanders across the top of the world. The wind blew ice into the side of the ship, making it difficult even to stay still, and the team only managed to get a few, small cores by dropping a weighted pipe off the back of the ship. “The ice does terrible things up there,” says Backman. “When I came out, I said I would never do that again without the proper vessels.”

Pole position

Now Backman has a second chance, as head of a mission that will return to Lomonosov in August. With US$12 million from the IODP, Backman will this time have at his disposal satellite-borne radar that can see through clouds, real-time weather updates, three ice-breaking escort vessels, and an oil-industry drilling ship, on which the party will steam to a location 130 kilometres south of the North Pole. There Backman hopes to sink three holes into the ridge and retrieve 500 metres of cored sediments, which will give a glimpse of the past 50 million years. The sediments will be examined for minerals that have been transported by ice from nearby land, or fossils of tiny creatures that thrive in specific climates — tell-tale signs of when the pole was free of ice, or completely iced over.

With an onboard geology lab and the ability to drill 7 km beneath the sea floor, the Chikyu aims to find out why Japan is plagued by earthquakes.

If the mission succeeds, it will be a coup for climatologists, for whom the North Pole's ancient climate is still a mystery. But the IODP has other ambitious projects in mind too. Along with its ice-breaking facilities, provided mainly by the European project members, it will also have a Japanese ship designed to drill deep into the Earth — the US$500-million Chikyu. Unlike the Resolution, which was an old oil-exploration vessel converted for use by scientists, the Chikyu has been designed from the keel up specifically for research. The ship has equipment for dating and analysing cores that is more comprehensive than that in most land-based labs, says Millard Coffin, a marine seismologist at the University of Tokyo's Ocean Research Institute and chair of the IODP's Science Planning Committee. Most importantly, the ship has a half-metre-wide pipe that can extend from the ship's bottom to the sea floor in water up to 2,500 metres deep. A 14-centimetre pipe fits inside this 'riser', through which a drill can then bore a further 7 km into the Earth.

This impressive drilling capacity will allow the Chikyu to drill into untouched areas of Earth's interior. So far, everything dug up has been from the upper portion of the crust, a layer of rock that is an average of 75 km thick on land and 10 km thick in the ocean — although this varies from place to place. Geologists are fascinated to find out more about what is happening deeper still, in the zone called the mantle. This region, which extends for 2,800 km beneath the crust, carries heat from Earth's core towards the surface and helps to drive plate tectonics. Although heated to more than 1,000 °C, the rock here is not molten, thanks to high pressures, but moves plastically over long time scales. “This is the Earth's heat engine that makes everything happen at the surface,” says Donna Blackman, a geophysicist at the Scripps Institution of Oceanography in La Jolla, California.

The division between the crust and the mantle has been studied with seismic waves, revealing a marked difference in physical properties between the two layers. But no one is sure whether this is because the rocks have different mineral compositions, or have simply been altered by the pressure, the presence of liquid, or some other factor. Researchers have pulled up samples of mantle rock that have been thrust towards the surface, but no one has managed to study it in its native environment. Retrieving such a sample would fill in a lot of the gaps in our knowledge, helping geologists to understand better how heat flows through the mantle and to interpret the results of seismic tests.

In the Chikyu, Japan has created a ship that can pierce the ocean's relatively thin crust and dig into the mantle — although it won't be easy. To reach the mantle in relatively shallow waters of 2,500 metres, the vessel will have to drill into an ocean spreading ridge — a place that sits high in the water and where the crust is thin enough for a 7-km drill bit to get through it. But these spreading zones are incredibly hot — up to 1,200 °C at depth. No one has yet designed a drill to deal with these temperatures, so it is hard to know how easy it will be to extract cores of solid rock from this section of the mantle.

Although the Chikyu was designed with the aim of obtaining mantle rocks in mind, that feat is still a long way off — researchers don't expect it to happen for at least ten years. But Japan has a more pressing motive to drill deep into Earth — to learn more about earthquakes. Japan sits on four shifting tectonic plates and experiences hundreds of earthquakes a year. The fault line southeast of Japan, where the western edge of the Pacific Ocean slides beneath the Eurasian plate, experiences a major earthquake nearly every 180 years, and is one of the most active sites in the world.

Finding fault

One of the Chikyu's first missions will almost certainly be to drill straight into the heart of such a fault — a spot between 10 and 30 km down called the seismogenic zone, where the stress builds up between plates before they slip, causing an earthquake. “The material down there determines how the plates slide, but the truth of the matter is that no one knows exactly what it is,” says Kiyoshi Suyehiro, a geophysicist and executive director of the Japan Marine Science and Technology Center in Yokosuka. The Chikyu will be able to pull up material from a depth of 7 km — close enough to approximate the zone's geochemistry, says Jim Mori, a seismologist at Kyoto University. This should give a picture of the fault's mineral composition, along with factors such as grain size and water content, and will inform models of how the plates slide against each other. “Until now, earthquake models have always had to use a somewhat arbitrary constant for the friction that affects plate movement,” says Suyehiro.

The Chikyu has been built, but it will take some time for it to be fully fitted for work, and it is not scheduled to embark on its first scientific mission until October 2006. In the meantime, IODP researchers have some exciting plans for the Resolution too.

One focus for both the Resolution and the Chikyu will be to investigate the incredibly rich diversity of bacteria and other creatures that live up to 1 km below the sea floor — a biological treasure trove uncovered by ODP missions over the past four years. The IODP will enlist more microbiologists to study these life forms, some of which are thought to have lived for 200 million years in environments of extreme pressure and temperature, without sunlight or oxygen. Examination of these bacteria will fill evolutionary gaps in the bacterial family tree, says microbial ecologist Kenji Kato of Shizuoka University in Japan.

The researchers will be keen to learn more about how these bacteria interact with the rock around them. “We are going to examine some riddles about how microorganic life cycles affect geochemical processes and vice versa,” explains Kato, the sole biologist on the IODP's Science Planning Committee. One such riddle is the question of whether and how bacteria are responsible for the production of methane gas that occurs under the sea floor and feeds the formation of hydrates — icy blocks that hold molecules of methane in cages of water. Some researchers claim that large pockets of this greenhouse gas have erupted in the past, triggering climate change and even sinking ships. Much of the methane is thought to be produced in the breakdown of organic matter by bacteria, but no one really knows what bacteria are responsible, where they live, or how fast they produce the gas.

To answer these questions, researchers will have to drill into these methane hydrate layers, potentially releasing the explosive pockets of gas trapped beneath. Drilling ships have to be extremely careful around such pockets, as methane bubbles can burst explosively through the drill pipe, causing massive damage to both the pipe and the ship. But the Chikyu's design should be equal to the task — a 'blow-out protector' installed at the base of the riser pipe on the sea floor can seal both the riser and drill pipes when an area of high pressure is encountered. Drilling into these pockets will be interesting not only to researchers, but also to companies interested in mining the natural gas as a potential fuel.

Together, the IODP's ships and expertise combine to make a very ambitious programme. But some problems remain to be solved if the plan is to bear fruit. The IODP already faces a budget crunch. US researchers had hoped to begin development next year on a new ship to replace the Resolution, but that project has been shelved for the time being, and the Resolution may simply be overhauled instead.

Unequal arrangement

Meanwhile, the European consortium has pledged less money than was originally hoped for by the United States and Japan, making Europe, for now, a less-than-equal partner in the project. This means that there will only be enough money for one or two European projects a year — Coffin and other IODP members had originally hoped for as many as eight. Those projects are meant to provide equipment on lease for specific missions — such as ships that can handle Arctic conditions or drill in shallow coastal waters.

Funding issues could also pose problems in Japan, which had hoped that Europe would help to fund missions involving the Chikyu. Japanese scientists do not yet have enough money for equipment that will slot into the holes drilled at the fault line, for example, which would monitor the chemical, physical and biological properties of the sediments during a quake. And prospects are not bright for Japan's hopes of extending the Chikyu's drilling capacity so that it can reach the sea floor in waters 4,000 m deep — the average depth of the ocean. If this feat can be achieved — something that the oil-drilling community has never managed with a riser apparatus — the Chikyu will be able to drill into the mantle in deeper waters where the rock is much cooler, making samples easier to obtain.

But whatever obstacles they face, researchers are steaming ahead with the plan. At the very least, they can keep up the ODP's old reputation for collecting vast amounts of samples and data. Hopefully they will extend the programme's reputation for astounding discoveries too.