Fluid chemistry of the low temperature hyperalkaline hydrothermal system of Prony Bay (New Caledonia)

Researchers have uncovered the unique fluid chemistry of Prony Bay's hyperalkaline hydrothermal system, revealing a distinct low-temperature environment unlike any other known serpentinizing systems. The study identified submarine vents discharging high-pH fluids (up to pH 11) with temperatures reaching 37°C and hydrogen-rich gases (12-30% H₂). Chemical analysis of 45 water samples from six sites showed that these fluids, originating from meteoric sources, mix with seawater, creating sharp gradients in pH, salinity, and dissolved elements. Notably, the system exhibits supersaturation of Mg- and Mg-Ca carbonates at pH ~10, indicating active brucite formation due to reducing conditions. Unlike fully continental or marine systems (e.g., Oman or Lost City), Prony Bay's hyperalkaline discharge is unique, offering insights into serpentinization processes in ultramafic environments.

Monnin, C., Chavagnac, V., Boulart, C., Ménez, B., Gérard, M., Gérard, E., Pisapia, C., Quéméneur, M., Erauso, G., Postec, A., Guentas-Dombrowski, L., Payri, C., & Pelletier, B. (2014). Fluid chemistry of the low temperature hyperalkaline hydrothermal system of Prony Bay (New Caledonia). Biogeosciences, 11(20), 5687–5706. https://doi.org/10.5194/bg-11-5687-2014