Geologist Maps Underseas Terrain in Massachusetts
BOSTON — When geologist Page Valentine steams out for a trip off the state’s picturesque coastline, he’s far more interested in what he can’t see. Valentine has been using sophisticated sonar to map 1,400 square miles of ocean floor off the Massachusetts coast for 11 years.
He’s discovered networks of underwater ridges and valleys, the remains of long-forgotten shipwrecks and underwater gouges left by ancient icebergs.
Valentine sees the maps as a basic tool for government regulators who must manage the miles of hidden land. The maps can also point fishermen toward productive areas, direct more efficient placement of underwater cables and give researchers the location of vulnerable or changing ocean habitats.
"These submerged lands off our shores are a huge area about which we know very little. … You need a map," said Valentine, a researcher with the U.S. Geological Survey in Woods Hole.
The project to map the Stellwagen Bank National Marine Sanctuary and the area around it began in 1994, shortly after it was created. The 840 square mile sanctuary is a busy shipping and fishing area about 21 miles east of Boston where marine life and habitats are under federal protection.
The first phase mapped the general topography of the sea floor. The second captured photographic images of the bottom. The third set, to be completed in about 2008, will map plant and animal life and habitats.
The ocean floor is mapped by equipment that sends 60 to 120 sonar beams bouncing off the bottom as a boat sweeps the surface. The sonar can measure the varying depths, as well as how hard the floor is in certain spots, with a weaker signal indicating a softer surface, such as mud.
Researchers are also using a sophisticated camera system which floats centimeters above the seabed, filming and taking pictures to help map the bottom’s biology and geology.
The years of study have uncovered gouges in the floor, kilometers long, left from icebergs that grounded in the shallow waters of Stellwagen Bank 10,000 years ago and melted.
More than 50 shipwrecks have also been found, Valentine said, though identifying specific ships is difficult because the resolution of the mapping isn’t fine enough – the wrecks simply appear as unusual shapes on the bottom.
The maps helped workers take a southern route around a rough-bottomed area off Jeffreys Ledge, just off Cape Ann, and lay a fiber-optic cable connecting Europe to Massachusetts.
The mapping has also better defined the boundaries of underwater ledges, as well as areas of hard and soft bottom, of which fishermen have had general knowledge for centuries. More precise mapping helps fishermen better approach the margins of rough terrain, where fish often congregate, without snagging their gear. Or, it can help them avoid rough areas altogether, said Bob Reid, chief of coastal ecology at the Northeast Fisheries Science Center.
The mapping can give clues about where commercially valuable species can be found. Certain fish, such as yellowtail flounder, find food near sandy-bottomed areas. Cod often prefer hard gravel bottoms. All fish are dependent on the ocean floor, and managers want to determine which areas most need protection.
"Some habitat types are more vulnerable than others and we want to know that," Reid said
Besides scientists, Valentine has given the maps to commercial and recreational fisherman and whale watch operators interested in showing customers the lay of the land they’re floating over. Valentine said the enthusiasm that greets the maps can be explained as excitement over a look at what’s always has been hidden.
"It’s like solving a mystery," he said.
On the Net:
Stellwagen mapping project: http://woodshole.er.usgs.gov/project-pages/stellwagen/index.html