FY 1997

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

Ishibashi, J., H. Wakita, K. Okamura, E. Nakayama, R.A. Feely, G.T. Lebon, E.T. Baker, and K. Marumo

Geochim. Cosmochim. Acta, 61(3), 485–500 (1997)

Onboard analyses of dissolved CH and Mn were conducted on the water column along the southern East Pacific Rise between 13°50 and 18°40S 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 CH/Mn ratio in the plumes shows wide variability ranges from about 0.05 to 3.9 due to the wide range of CH concentration. The CH-rich plumes were detected in the region of 16°00-18°40S where a vigorous magmatic budget was confirmed by previous studies. Moreover, the CH/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 CH/Mn variability in the southern EPR plumes, based on the analogy of the case at the EPR 9°50N 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.