Recent underwater explorations have revealed unique hot spots of biogeochemical activity at several submerged groundwater vents in Lake Huron, the third largest of the Laurentian Great Lakes. Fueled by venting groundwater containing high sulfate and low dissolved oxygen, these underwater ecosystems are characterized by sharp physical and chemical gradients and spectacularly colorful benthic mats that overlie carbon-rich sediments. Here, typical lake inhabitants such as fish and phytoplankton are replaced by communities dominated by microorganisms: bacteria and archaea that perform unique ecosystem functions. Shallow, sunlit sinkholes are dominated by photosynthetic microorganisms and processes, while food webs in deep aphotic sinkholes are supported primarily by chemosynthesis.
