EVOLUTION OF EAST PACIFIC RISE HYDROTHERMAL VENT FLUIDS FOLLOWING A VOLCANIC-ERUPTION

STUDIES of sea-floor hydrothermal vent fluids have shown them to have stable characteristics on a decade timescale(1), with temperatures in the range 350 +/- 30 degrees C (ref. 2) and chemistries(2) that vary f rom vent to vent, which have most recently been interpreted to reflect phase separation within the hydrothermal system(3-7). Here we report measurements of vent fluid temperature and chemistry from 9 degrees 46 .5' N on the East Pacific Rise, which show unprecedented variability o n timescales of only a week. Our measured temperatures range up to 403 degrees C, placing the fluids unequivocally in the vapour field at th e sampling conditions. Consistent with the fluids being in the vapour phase are the lowest chlorinities and silica contents, and highest hyd rogen sulphide contents, yet reported for sea-floor vent fluids, These unusual fluid characteristics are the result of a volcanic eruption h aving occurred at this site, within weeks of when the first measuremen ts were made(8). The hydrothermal system in the immediate post-eruptiv e period is thus characterized by previously unknown temperature and c hemical characteristics, necessitating revisions to models of hydrothe rmal fluxes to the oceans.