Global hydrothermal primary production rate estimated from the southern East Pacific Rise

It had been speculated that photosynthetic primary production in the surface ocean regulates microbial production in deeper seawater layers through rapid transportation in biogenic products via dense, heavy faecal pellets excreted by zooplankton. Recent findings, however, on numerous microbial populations in deep-sea hydrothermal environments (i.e. Karl et al., 1980; Winn et al., 1986; Maruyama et al., 1993) are changing conventional concepts on the deep-sea microbial world. This is because volatile and reduced compounds derived from axial magma or the earth's mantle as dissolved in the hydrothermal system, such as methane, hydrogen, hydrogen sulphide, manganese and iron, stimulate the chemosynthetic growth of microorganisms even at deep-sea levels. To date, however, little is known about the microbial chemosynthetic primary production rate in global hydrothermal environments, in contrast to the large number of reports on photosynthetic primary production rate in the euphotic marine surface. Huge amounts of volatile and reduced compounds discharged from worldwide hydrothermal activity appear to transfer substantial amounts of biogenic material from ocean-bottom marine environments. Higher biological production and biogeochemical processes in the area of global oceanic ridges presumably are greatly stimulated or modified by this upward flux of biogenic materials, including living microbes. Thus, top priority should be given to study on hydrothermal primary production rate in deep-see ecology. At prsent, however, we face difficulties in the estimation of the global hydrothermal primary production rate by such a direct method as measuring the in situ carbon assimilation rate common in euphotic surface marine research, because of the wide variety of energy sources and habitats of microorganisms in such extreme deep-sea environments.