Grand Valley State Scientists and Sanctuary Maritime Archaeologists Collaborate for June 2007 Sinkhole Project

Date: June 11-14, 2007
Entry by: Tane Casserley, Maritime Archaeologist, Maritime Heritage Program NMSP

Several sinkholes have been discovered within the Thunder Bay National Marine Sanctuary. These sinkholes are collapsed formations in the limestone rock that lay at depths that range from 21-92m on the lake bottom. Thunder Bay's underwater sinkholes were exposed during the last ice age when the waters of Lake Huron were more than 100m below the present level. Because of this, the sinkholes could contain human cultural remains, potentially well preserved in the lake's protective environment. Despite their significance, little is known regarding their hydrology, biology, and geochemistry of the sinkholes in the Great Lakes.

Ongoing research by Grand Valley State University's Dr. Bopi Biddanda and Scott Kendall, and University of Wisconsin's Dr. Steve Nold has discovered that the Thunder Bay sinkhole ecosystems are biogeochemical hotspots of microbial and geochemical activity. To collect water samples and deploy instruments measuring salinity and conductivity archaeologists Tane Casserley (MHP), Russ Green (TBNMS), and Joe Hoyt (ECU) aided the researchers by becoming their eyes and hands on the lake bottom. Used to working in fragile environments and conducting delicate work, archaeologists have a unique skill set that can be of immense value to multi-disciplinary science missions. Working in 21m of water the archaeologists worked over 4 days with a typical water temperature of 34F.

Diving in this unique ecosystem the divers had to use extreme care not to disturb the diverse varieties of anaerobic bacteria that abound in this oxygen poor environment. By exhibiting excellent buoyancy control learned after years of diving on fragile shipwrecks, they were able to accomplish complex tasks all the while hovering inches above the delicate bacteria mat below them. The assignment was made even more complex by a water density change approximately 2m above the bottom which can be seen as a haze layer or lens above the bottom. It was a new experience for the archaeologists and there are already plans for next year's sinkhole project for the two sciences to collaborate together again.