Chemosynthetic Primary Production at East Pacific Sea Floor Spreading Centers

Abstract

These vents, as commonly termed, were found to be surrounded by dense populations of benthic animals. Especially striking were the tightly packed clusters of mussels, clams (Fig. 2), and vestimentiferan tubeworms of unusual size (Ballard 1977, Corliss et al. 1979, Galapagos Biology Expedition Participants 1979). Early in 1979, more vents were located and visited by Alvin west of the original diving area and also further north along the East Pacific Rise spreading zone near the Mexican coast (see Fig. 1). What is the food supply that sustains these unusually rich communities, which are located at an ocean depth far removed from surface waters of only moderate photosynthetic production? An explanation discussed in a preliminary communication by Lonsdale (1977) proposes thermoconvective currents caused by rising warm water, which may lead to an entrainment of nutrient-rich bottom water. An alternate hypothesis originated from one of the first direct observations from the portholes of Alvin at close range: The most active vents emitted milky bluish water. This indicated the possible presence of suspended particulate or colloidal sulfur as a product of spontaneous oxidation and thereby the potential for bacterial oxidation of reduced sulfur species. The presence of hydrogen sulfide was soon confirmed. Since this process involves the conversion of inorganic into organic carbon, as in photosynthesis, the possibility arose that those unusual deepsea populations might be supported by primary