Hydrothermal activity at Hook Ridge in the Central Bransfield Basin, Antarctica

Hydrothermal activity in the Central Bransfield Basin revealed an active lo w-temperature vent field on top of a submarine volcanic structure. A temper ature anomaly was detected and the sea floor showed various patches of whit e silica (opal-A) precipitate exposures and some yellow-brown Fe-oxyhydroxi de crusts. Enriched dissolved methane concentrations were encountered. Sedi ment was near 24 degrees C just after the grab came on deck. No dense popul ation of chemosynthetically based macrofauna known from other hydrothermal venting areas was present, except for pogonophora. The observations suggest that the sedimented hydrothermal field at Hook Ridge is a low-temperature end-member branch from a deeper hydrothermal source.