An extensive v~deoscopic study of a h~gh-temperature sulfide structure on the Juan d e Fuca Rldge (northeast Pacific) examined temporal variation in vent community distnbution and l~n k s between faunal and environmental changes V~d e o imagery was acquired d u l~n g a total of 5 manned submersible and ROV (remotely-operated vehicle) dive programs between 1991 a n d 1995 The structure was systemat~cally mapped for each year of the study and a serles of analytical tools was developed to quantify changes in biological and geological features and observable flow patterns Results shoiv ( l ) heterogeneous faunal distnbution, characterized by decimeter-scale patchiness and general absence of vertical gladients, (2) apparent links between commun~ty d~stnbution, and environmental features such as fluid flow patterns, substratum and temperature/chemicdl conditions, (3) a significant influence of perturbations on community dynamics, (4) dbsence of d~r e c t~o n a l biological succession at the time scale examlned (years) Overall, these observations strongly suggest that many hydrothermal community changes are initiated by gradual and ablupt flow mod~fications Results are compiled in a dynamic succession model for sulfide edifices where community transitions are dnven by flow vanatlons, and by biolog~cal processes operating at sub-annual t~m e scales CVe conclude by stressing the need for extended momtonng of short-term dynamics in order to understand the relationslup between hydrothermal communities and their environment
Three-quarters of the Earth's volcanic activity is submarine, located mostly along the mid-ocean ridges, with the remainder along intraoceanic arcs and hotspots at depths varying from greater than 4,000 m to near the sea surface. Most observations and sampling of submarine eruptions have been indirect, made from surface vessels or made after the fact. We describe here direct observations and sampling of an eruption at a submarine arc volcano named NW Rota-1, located 60 km northwest of the island of Rota (Commonwealth of the Northern Mariana Islands). We observed a pulsating plume permeated with droplets of molten sulphur disgorging volcanic ash and lapilli from a 15-m diameter pit in March 2004 and again in October 2005 near the summit of the volcano at a water depth of 555 m (depth in 2004). A turbid layer found on the flanks of the volcano (in 2004) at depths from 700 m to more than 1,400 m was probably formed by mass-wasting events related to the eruption. Long-term eruptive activity has produced an unusual chemical environment and a very unstable benthic habitat exploited by only a few mobile decapod species. Such conditions are perhaps distinctive of active arc and hotspot volcanoes.
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