Hydrothermal methane and manganese variation in the plume over the superfast-spreading southern East Pacific Rise

Onboard analyses of dissolved CH, and Mn were conducted on the water column along the southern East Pacific Rise between 13 degrees 50' and 18 degrees 40'S during the 1993 RIDGE FLUX Cruise. Many hydrothermal plumes were identified by chemical anomalies which overlie more than half of the surveyed ridge crest. The CH4/Mn ratio in the plumes shows wide variability ranges from about 0.05 to 3.9 due to wide range of CH4 concentration. The CH4-rich plumes were detected in the region of 16 degrees 00'-18 degrees 40'S where vigorous magmatic budget was confirmed by previous studies. Moreover, the CH4/Mn ratio of the plumes is highly correlated with other volatile/metal parameters such as the S/Fe ratio in plume particulate. These results strongly suggest that volatile input caused by magmatic perturbation to hydrothermal systems is responsible for the CH4/Mn variability in the southern EPR plumes, based on analogy of the case at the EPR 9 degrees 50'N site. The detection of several volatile-rich plumes and the extensive hydrothermal flux of volatile species are attributed to frequent magmatic events in the superfast spreading southern EPR. Copyright (C) 1997 Elsevier Science Ltd.