Ninety percent of the world's seafloor consists of normal seafloor or has seamounts similar to the types of crust recently sampled, Johnson says. And most of that even seafloor that's much older, 100 million years or more is similar to the 3.5-million-year-old sites sampled as far as porosity of the rock, the sediment cover and rock temperatures of between 100 and 160 F, he says. The rocks at the sites on the Juan de Fuca plate are at the higher end of the range for 3.5 million-year-old crust because sediments covered them at a very young age.
University of Washington doctoral student Julie Huber and her advisor, John Baross, are working with samples of live microbes from the expedition. Some UW laboratory work shows bacteria extracted from seamount flanks grow best at hot temperatures, 190 F, which is considerably higher than the 68 F fluid they were collected with and the 140 F temperature of the rocks in that area. This means that the fluid and microbes are coming from deeper within the ocean crust, perhaps as deep as half a mile below the seafloor.
Cell counts at most of the sites are higher than cell counts from normal seawater, a strong indication the scientists were sampling a crustal environment and that their samples were not contaminated with bottom seawater.
Another important concern involves possible contamination from the process of drilling. This is a critical question even for a hole drilled by the International Ocean Drilling program in 1997 that has been gushing copious crustal fluids since then. There is a chance that drill hole, sampled for work reported in both the Science and Eos articles, was contaminated during drilling or that mic
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Contact: Sandra Hines
shines@u.washington.edu
206-543-2580
University of Washington
18-Mar-2003