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First dives made at 7 South site

(click on the text below each image for an enlargement)


Greg O'Mullan





by Bob Vrijenhoek, chief scientist

We had three successful dives to 2750 meters at the 7 South locality. These are the first dives to this part of the East Pacific Rise, part of the mid-ocean ridge system that circles the globe for 40,000 miles much like the seams on a baseball.

The organisms living in these environments can experience extreme temperatures and chemicals that would be highly toxic to humans. Temperatures in excess of 400 Celsius have been recorded along this oceanic ridge system.

The high temperatures are the result of ocean water seeping through cracks in the lava and being heated by the magma chamber below. The superheated water leeches metals and minerals from the rock and is emitted in hot springs, geysers and gentle seeps. The organisms pictured here were taken from a seep in which temperatures only reached 4 Celsius.

The vent ecosystem depends on bacteria that can use hydrogen sulfide (H2S), the gas that causes the smell of rotten eggs. H2S is an energy-rich compound associated with volcanism and would be highly toxic to us in these concentrations. The bacteria use the energy from H2S to turn carbon dioxide and water into sugars, very much like plants use the energy from sunlight to make sugars from carbon dioxide and water.

The bacteria are eaten by grazing or filter-feeding animals, such as the limpets. Other kinds of bacteria are symbionts that live in the tissues of tubeworms and mussels. These bacteria provide nutrients to their worm and mussel hosts. The tubeworms have no mouths or guts, so they depend completely on their bacteria for nutrition. When the sulfide springs die, the bacteria die and so do the worms and mussels.

Local extinction events appear to be common along this part of the mid-ocean ridge system. We visited several sites where all the tubeworms were dead and only empty tubes remained. These organisms must have good abilities to grow fast and produce offspring that can disperse and colonize new springs as they form on the ocean floor. We are using genetic technology to try to estimate the dispersal abilities of these organisms.

Samples of tubeworms, limpets and mussels were collected for subsequent genetic analyses. One goal of these studies is to see how these organisms relate to similar organisms found north of the equator on the East Pacific Rise. We still have 27 days and 20 dives to go on this cruise and we will be sampling many more organisms and visiting sites that no one has ever before seen.

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