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 from 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 on timescales of only a week. Our measured temperatures range up to 403 degrees C, placing the fluids unequivocally in the vapour field at the sampling conditions. Consistent with the fluids being in the vapour phase are the lowest chlorinities and silica contents, and highest hydrogen sulphide contents, yet reported for sea-floor vent fluids, These unusual fluid characteristics are the result of a volcanic eruption having occurred at this site, within weeks of when the first measurements were made(8). The hydrothermal system in the immediate post-eruptive period is thus characterized by previously unknown temperature and chemical characteristics, necessitating revisions to models of hydrothermal fluxes to the oceans.