GPS Location : N45° 11.898' W83° 19.668'
Depth: 75 Feet
Description: Underwater explorations have revealed unique hotspots of biogeochemical activity at several submerged groundwater vents in Lake Huron, one of which is the Middle Island Sinkhole. Since groundwater emerging from these sinkholes contains high sulfate and low dissolved oxygen, they have created a unique habitat lacking the usual fish and metazoan communities found in Lake Huron. Instead, sinkholes are dominated by single-celled microorganisms such as Bacteria and Archaea.
In shallow, sunlit sinkholes (less than 100 feet deep), spectacular purple mats are created by photosynthetic cyanobacteria. In addition to substantial production by the photosynthetic mats at the surface of the sediments, sinkholes act as carbon sinks, effectively trapping falling phytoplankton production in organic-rich sediments underneath the cyanobacterial mats. NOAA and its partners have carefully studied the Middle Island Sinkhole and they are learning much about microbial diversity and activity in these unique habitats.
Only experienced divers should attempt this dive!