Anchialine blue holes found in the interior of the Bahama Islands have distinct fresh and salt water layers, with vertical mixing, and dysoxic to anoxic conditions below the halocline. Scientific cave diving exploration and microbiological investigations of Cherokee Road Extension Blue Hole on Abaco Island have provided detailed information about the water chemistry of the vertically stratified water column. Hydrologic parameters measured suggest that circulation of seawater is occurring deep within the platform. Dense microbial assemblages which occurred as mats on the cave walls below the halocline were investigated through construction of 16S rRNA clone libraries, finding representatives across several bacterial lineages including Chlorobium and OP8. In many blue holes, microbial metabolism of organic matter in the presence of seawater sulfate leads to anoxic and sulfidic conditions at or below halocline. Sunlight penetrating this sulfidic layer allows for in situ primary production to be dominated by bacterial anoxygenic phototrophs. Although water column chemistry and molecular genetic diversity of microbial mats in Cherokee Road Extension Blue Hole were investigated in this study, the full scope of the biogeochemistry of inland blue holes throughout the Bahamas Archipelago is complex and poorly understood. However, these microbial communities are clearly influenced by several factors including solar insolation, terrestrial and marine inputs of oxygen, carbon, and nutrients, water residence times, depth to the halo/chemocline, and cave passage geometry. The biogeochemistry of inland blue holes throughout the Bahamas is so distinctive which makes Abaco Island and the rest of the archipelago valuable as natural experiments, repositories of microbial diversity, and analogs for stratified and sulfidic oceans present early in Earth's history.
