The icy waters of Ikka Fiord hold the secret to an elusive mineral. Paul Seaman dives in
There is a legend in Greenland that tells how the Inuit people drove invaders out on to the thin ice of a frozen fiord. The ice gave way, they all plunged through, and perished in the icy water. Today, if you look down through the sheltered waters of Ikka Fiord, you seem to see their petrified remains standing motionless on the bottom: the warriors and their families; mothers, children, all.

This summer, six young British divers went to this obscure fiord to look for an enigmatic mineral that has kept its secrets for more than three decades. For the "figures" at the bottom of Ikka Fiord represent one of geology's rarest treasures. The underwater columns, first identified in 1963 by the Danish geologist Hans Pauly while on a picnic with officers in the Royal Danish Navy, are made of ikaite, an unusual, high-pressure form of chalk or limestone known as calcium carbonate hexahydrate (CaCO3.6H2O).

Ikaite is normally formed at enormous pressures, 3,000 times that of normal atmospheric pressure. It is a metastable mineral with the remarkable property that, at temperatures a few degrees above 0C, it melts away like ice. This characteristic means that the mineral, which may well be very common in the sediments of the deep ocean floor, has seldom been seen by geologists. By the time drill-cores taken from the sediments are winched back on to surface ships the ikaite will have vanished, leaving behind, like the smile of the Cheshire Cat, a "pseudomorph" that is just the impression of the mineral within the core.

Only about five other findings of ikaite have been reported from around the world, including two from deep-sea cores recovered from the abyssal plains. One finding by the research ship Glomar Challenger nearly caused a scientific and diplomatic incident, when British scientists suspected their Japanese colleagues of unscrupulously taking their rock specimens. In fact, thematerial that had mysteriously disappeared from a bench in their laboratory was ikaite, which had spontaneously and naturally vanished.

Ikaite will form only under specific chemical and temperature conditions at surface pressures. Consequently, if there are signs that it had once formed in a unit of sedimentary rock, it acts as a reliable indicator of conditions under which that rock was laid. Ikaite is similar to the gas hydrates found in great abundance on the seabed and which represent a potentially vast energy reserve. Studies of ikaite may cast light on these gas hydrates.

As a doctoral student at Imperial College, London, I wanted to know more about this mineral, so I and five friends found ourselves last summer diving in Ikka Fiord, where ikaite forms over springs issuing from the seabed under modest pressures, specific chemistry and a very bracing temperature of 2-3C.

A fortunate contact put us in touch with a zoological expedition from the Museum of Copenhagen that was also interested in Ikka Fiord from a marine biological and phycological point of view. On hearing about the importance of ikaite and our plans, they decided to extend their expedition to include geologists from the University of Copenhagen, principally the geochemist Dr Bjorn Buchardt. We worked in consultation with the Danes but not alongside them. This was mainly a practical arrangement as, surprisingly for such a sparsely populated site, camping space in the fiord was very limited if we were not to damage the thick growth of arctic willow that lines the shores.

With a clear list of scientific objectives and the promise of learning something new and potentially useful, we were surprised that our project attracted little interest - and even less capital.In the end, the expedition was funded largely by loans from parents and bank managers.

Capitalising on long hours of sub-arctic daylight, our team trawled back and forth in an inflatable dinghy, logging depths and columns using a sonar linked to global positioning satellites to pinpoint the positions. In this way we conducted a topographic and hydrographic survey of the seabed. A laptop computer allowed us quickly to compile and print the first map of the columns of Ikka Fiord in the field. We collected specimens of the rock and made a film record.

Bringing the specimens back to the UK wasan ordeal in itself. They had to be kept chilled, which meant begging fridge space from youth hostels and airports; in Copenhagen, they spent several nights in the veterinary morgue, with dead dogs and cats for company. The maps revealed that the bottom of Ikka Fiord sprouts columns for most of its length, although they take a variety of sizes and forms. In all we estimatethere must be a total of some 2,500 columns greater than 1m in height.

It is difficult to find a parallel to swimming among the columns of Ikka Fiord. The biggest, rising 15m to 20m from the bottom, are like giant, sugary stalagmites, whose tips frequently terminate in clasping hand-like forms that seem to be desperately reaching for air. Their flanks are adorned with marine life. Every dive was full of discovery, the columns distorted into many beautiful and grotesque shapes, like the spires and gargoyles of some overdone Gothic cathedral. At times the scenes were so captivating that I marvelled too long, ignoring the throbbing of my numb sinuses and fingers; this would lead to several minutes of agony after surfacing.

The warriors of Ikka Fiord, condemned to their lonely frigid existence, are refusing to surrender their secrets without a fight. What is no longer a secret is their existence. The Greenland government is being encouraged to protect and preserve this unique, fragile and beautiful site, which is part of a national park. This year was seen very much as a reconnaissance, raising more questions than it answered. Several members of the team are planning to return next summer with a second Danish expedition, intent on wooing the full story from these stony sentinels.