Prony Bay

Monnin et al. (2014): "terrestrial hyperalkaline springs of the Prony bay (southern lagoon, New Caledonia) have been known since the XIXth century, but a recent high resolution bathymetric survey of the seafloor has revealed the existence of numerous submarine structures similar to the well-known Aiguille de Prony, which are also the location of high pH fluid discharge into the lagoon", "Before the cruises on the R/V Alis in 2005... the only known submarine edifice was the pinnacle located in the middle of the Prony bay (“Aiguille de Prony”, Site ST07).", "The temperature difference between the venting fluids and the lagoon waters is not very large (about at most 15 C)."; Quéméneur et al. (2014): " shallow submarine hydrothermal field of the Prony Bay (New Caledonia) discharges hydrogen- and methane-rich fluids with low salinity, temperature (< 40 C) and high pH (11) produced by the serpentinization reactions of the ultramafic basement into the lagoon seawater. They are responsible for the formation of carbonate chimneys", "To our knowledge, the Prony Hydrothermal Field (PHF) is the only example of a shallow ultramafic-hosted submarine hydrothermal systems so far (at water depth < 50 mbsl).", "the highly alkaline PHF fluids have a low salinity inherited from their meteoric origin"; "...like the Lost City, the water that bubbles out of the Prony vents has an extremely basic, or alkaline, pH of around 11. Temperatures reach up to 40 C in some places, and fluids are highly enriched in dissolved hydrogen (H2) and methane (CH4). Calcium dissolved in the fluids reacts with bicarbonate in seawater, which leads to the formation of tall, monolithic calcite chimneys", "the main Prony chimney, called “the Needle of Prony” or “l’Aiguille” in French, nearly breaches the water surface"; there are also intertidal sites on Prony Bay; "The top of the Needle has no active venting, so the divers swam down the side of the chimney to a depth of about 12 meters (39 feet), where they began to see white-tipped, cone-like structures out of which hydrothermal fluids flow. The water coming out of the vents is fresh, not salty, causing it to shimmer when it mixes with the surrounding seawater... This freshwater distinguishes the Prony hydrothermal field from other sites such as Lost City, which are fed with saltwater."