A new habitat for chemotrophic ecosystems has been found beneath the former extent of the Larsen Ice Shelf in Antarctica. This is the first report of such ecosystems in the Antarctic. (Chemotrophic ecosystems derive their primary metabolic energy from chemical reactions other than those of photosynthetic origin.)An association of microbial mats and cold seep clam communities, is described, that thrived within an 850-m-deep glacial trough some 100 km, or more, from the ice shelf front. However, the continued existence of this unique ecosystem is uncertain, given the increased loading of sediment to the seafloor as a result of the ice shelf's collapse in early 2002. The vent-related ecology could have a methane source, based upon the vent's similarity with other cold seeps located along continental margins.