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An Underwater View of the Gulf of Maine Sea Floor
Geography of the Maine Coast and Submerged Lands
Sea-floor Relief and Geology
The ocean floor along the Maine coast is as rugged as the shoreline itself. The hills and valleys seen on land are influenced by the bedrock structure underlying the State of Maine. In a similar manner, the sea-floor relief - or bathymetry - mimics the bedrock structure (Figure 2). Relief along the inner continental shelf can easily reach 100 meters (over 300 feet) and often this relief is not far from the shoreline (Figure 3).
The sea-bed geology of Maine's inner continental shelf is primarily a complex mosaic of bedrock exposures (Figure 4) and muddy basins (Figure 5, Figure 6, and Figure 7). Rocky sea floor is dominant in water depths less than 50 meters. Muddy sea floor is dominant below 50 meters. Together, these two geologic categories account for 4/5ths of the sea floor.
Gravel plains and sandy sea floor make up about 1/5th of the ocean floor of state submerged lands. Gravel (including boulders) is a minor bottom type at all depths, but is most common in the 10 to 30 meter (30 to 100 feet) depth range (Figure 8, Figure 9, and Figure 10). Sandy sea floor is rare but present at all depths to 100 meters; sand is only slightly more abundant in water less than 30 meters deep (Figure 11).
The spatial complexity and details of sea floor geology are shown on MGS Open-File maps in the series entitled Surficial Geology of the Maine Inner Continental Shelf. A simplified illustration of the geology of the sea floor in a central location along the Maine coast from Cape Small to Schoodic Point is shown in Figure 12. In this illustration, sandy sea floor is most abundant offshore of the Kennebec River mouth. The outer portions of Penobscot Bay have abundant gravel areas and habitat suitable for juvenile lobsters. This region of Penobscot Bay sustains the most abundant lobster harvests along the Maine coast (Figure 13).
References and Related Web Sites
Barnhardt, W. A., Belknap, D. F., Kelley, A. R., Kelley, J. T., and Dickson, S. M., 1996, Surficial Geology of the Maine Inner Continental Shelf, a series of 7 maps covering coastal Maine, scale 1:100,000: Maine Geological Survey, Augusta, Maine.
Belknap, D. F., Gontz, A. M., Wahle, R., and Hovel, K., 2004, Mapping Lobster Habitat with Sidescan Sonar and ROV - A geologic and benthic oceanographic collaboration: Geological Society of America Abstracts with Programs, Vol. 36, No. 2, p. 137.
Kelley, J. T., 1998, Final Report on Surficial Mapping for the Penobscot Bay Project: National Oceanic and Atmospheric Administration Coastal Services Center.
Kelley, J. T., Barnhardt, W. A., Belknap, D. F., Dickson, S. M. and Kelley, A. R., 1998, The Seafloor Revealed - The Geology of the Northwestern Gulf of Maine Inner Continental Shelf: Maine Geological Survey, Open-File Report 96-6, 55 p.
MGS Field Locality Penobscot Bay 10,000 years ago
Penobscot Bay Marine Resources Collaborative, 1998, The Island Institute, Seafloor Geology report and geographic information system coverage (as in Figure 12).
Taylor, P. H. (editor), 2003, Mapping the Undersea Landscape (455KB pdf): Gulf of Maine Council on the Marine Environment, 4 p.
The Sea Around Us: Maine Coastal Program, State Planning Office
Funding to support some of the field work and mapping of sea-floor habitats in Penobscot Bay was made possible with funding from the National Oceanic and Atmospheric Administration, National Environmental Satellite, Data, and Information Service as part of the Penobscot Bay Marine Resources Collaborative through the Island Institute. Underwater images were taken by the M-Rover operated by Guy Meadows and Hans van Sumeren of the University of Michigan for a joint Maine Geological Survey - University of Maine effort to ground-truth sea-floor mapping with side-scan sonar. Additional funding to map the inner continental shelf was provided by the Department of Interior, Minerals Management Service to the Maine Geological Survey.
Text by Stephen M. Dickson
Originally published on the web as the May 2004 Site of the Month.
Last updated on April 23, 2012
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