Although the divers wear specially made gloves, the cold is felt in the hands.

"Hands are always a problem because it's the part of the body which is most sensitive to cold," Halbach explains.

"We generally stay 30 to 45 minutes in the water. We can stay up to 90 minutes but by that point, your hands are really cold," adds Schwanitz.

Beyond the discomfort, it can also hamper the precision of the work they are sometimes required to do in the depths, adjusting both photographic equipment and fixed underwater instruments for measuring temperature, light and water clarity, as well as gathering samples.

The rest of the body is well protected against the cold with divers wearing Arctic cold-water wetsuits, which are 7-millimetres (0.2 inches) thick.

"We also wear warm undergarments like for skiing," says Bender, who has a doctorate in marine biology from Rostock in Germany. Between their bulky suits and ballast weighing 18 to 20 kilos (up to 44 pounds), the divers are each carrying a weight of around 40 kilos. Aside from the cold, security is another big worry for the trio -- and for their insurers who lay down very specific demands. When one of them enters the water "another is ready to dive in in case of a problem, while the third is in charge of the boat," Schwanitz says.  In 2005, the installation of a decompression chamber -- indispensable in event of an accident -- has made procedures much simpler. Previously, they would check every morning to see if the weather was sufficiently good to allow a plane to come from Longyearbyen, the main town on Spitzberg, in case of an emergency, to fly someone to mainland Norway where the nearest decompression equipment was located -- a journey of some four hours. But in the 10 years since it was installed, the chamber has has only ever been used in practice exercises. "We usually dive to depths of 18-20 metres (up to 65 feet)," explains Schwanitz, patting the side of the cylindrical white chamber. "Most experiments here are done at that depth, so they are safe dives." afp