Minerals Report - International Seabed Authority

1. Introduction
Hydrothermal Activity at Mid-Ocean Ridges represents one of the
fundamental processes that control the exchange of thermal energy and
materials from the Earth's interior to the oceans. Thus, hydrothermal
interactions profoundly influence the composition of the ocean crust and
seawater. In addition, hydrothermal vent areas support diverse and unique
biological populations by means of microbiological communities which link
the transfer of thermal and chemical energy from the Earth to the production
of organic carbon. It was during an expedition in 1977 to the Galapagos
Spreading Centre that low-temperature (10-30°C) hydrothermal activity was
first discovered (Corliss et al., 1979). That was followed by a further French-
American expedition in 1981 that discovered high-temperature (350°C)
hydrothermal activity for the first time, on the East Pacific Rise (Spiess et al.
1980). Since then, more than 100 different new sites of active hightemperature
hydrothermal venting have been found, around the world’s
oceans - yet more than 50% of the total 60,000km of globe-encircling ridge
crest remains unexplored for hydrothermal activity. This paper summarises
the work currently undertaken by national and international programmes to
continue this exploratory work, to understand the geological processes which
control the distribution of hydrothermal venting throughout the world’s
ocean basins and to determine their role in maintaining the global vent
ecosystem.
2. Background: Hydrothermal Vents, What are they? How do they
work?
The pattern of hydrothermal circulation is one in which seawater
percolates downward through the fractured seafloor towards the base of the
oceanic crust and, in some cases, close to molten magma. In these hot rocks,
the seawater is progressively heated and undergoes chemical reaction with
the surrounding host basalt. As it is heated, the water expands and its
viscosity reduces. If these processes occurred on land, at atmospheric
pressure, catastrophic explosions would occur as temperatures would rise
above 100°C and the water would turn to steam. However, because midocean
ridges typically lie under 2000-4000m of seawater, at pressures 200-400
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