Manganese and methane anomalies in the North Fiji Basin

Abstract

In an effort to identify back-arc seafloor hydrothermal activity in the North Fiji Basin (NFB), five hydrocasts were made along the NFB spreading center between 15°S and 17°S during January 1987. Near-bottom anomalies in total dissolvable manganese (TDM) and methane were approximately five times background over the NFB triple junction. At four stations over the northwest portion of the spreading center, a mid-depth TDM anomaly of 2–5.5 nmol kg −1 was observed between 2 and 2.5 km depth; it has no associated anomaly in methane and extends along-axis at least 140 km north of the triple junction. A recently discovered, active ydrothermal system on the NFB triple junction is a likely source for these water column anomalies. A single hydrocast made over a small basin northwest of Viti Levu showed elevated near-bottom methane and TDM (approximately twice and four times background, respectively) of either hydrothermal or sedimentary origin.