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), doi: 10.1016/S0016-7037(96)00304-3, 485–500 (1997)

Onboard analyses of dissolved CH₄ and Mn were conducted on the water column along the southern East Pacific Rise between 13°50′ and 18°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 the wide range of CH₄ concentration. The CH₄-rich plumes were detected in the region of 16°00′-18°40′S where a 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 the analogy of the case at the EPR 9°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.