Water column pH and Al anomalies observed in the Manus Basin by Gamo et al. (Deep-Sea Research I, 40, 1993, 2335-2349) ∼200 m above their suspected source led them to suggest a high temperature (200-300°C), low pH hydrothermal fluid. However, the pH anomalies were more likely to have been caused by CO 2 /H 2 S-rich fluids. In addition, solubility constraints suggest that the source of the observed Al anomalies at this site is not high temperature (200-300°C), low pH hydrothermal fluids. Instead, the data seem to suggest the issuance of fluids by some non-steady state volcanic/hydrothermal process.