Sulfur hazard in the deep.

While boring into the seafloor off the coast of Oregon, marine scientists pulled up a nasty surprise late last year. Several cores of rock collected during the drilling held extremely high concentrations of dangerous hydrogen sulfide gas.

"Ever since the beginning of scientific ocean drilling, which goes back to the 1960s, I don't think anybody's recovered a core that's so rich in hydrogen sulfide as this stuff was," says Timothy J. G. Francis, deputy director of the Ocean Drilling Program (ODP) in College Station, Texas.

When the crew brought the cores up to the ship, the rock gave off potentially lethal doses of gas, forcing the workers to don special breathing equipment, Francis and Robert E. Olivas note in the July 13 Eos. The ODP team encountered the hazardous rocks while drilling into a thick accumulation of sediments in 674 meters of water. The researchers believe the sediments contained hydrogen sulfide in the form of a gas hydrate, an icelike structure kept solid by the tremendous pressures and cold temperatures of the deep ocean.

Although they could not make direct measurements, the ODP scientists believe the water near the seafloor also contained dangerous concentrations of hydrogen sulfide. Francis says the drilling operation itself probably melted some of the gas hydrates, releasing hydrogen sulfide into the water. But if the deep ocean in this region normally holds significant concentrations of this gas, it could damage submersibles or other equipment visiting the site, he says. Because the area has geologic importance, submersibles have explored near there in the past.