The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration’s National Marine Sanctuary Program, conducts seabed mapping and related research in the Stellwagen Bank National Marine Sanctuary region, an area of approximately 3,700 square kilometers (km2) that is subdivided into 18 quadrangles. The region lies offshore of Boston, Massachusetts, extending from Cape Cod in the south to the southern part of Jeffreys Ledge in the north (see location map below). 

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New online maps (see maps, below) portray the physical characteristics of the seabed in quadrangle 6 (211 km2) at a scale of 1:25,000. The mapped region ranges in depth from 30 to 185 meters and includes the shallow eastern flank of Stellwagen Bank and a group of small banks and valleys of glacial origin that lie in deeper waters to the east. Interpretations of seabed substrates, topographic features, and geologic processes are based on: a) multibeam sonar bathymetric and backscatter imagery that show topography and the relative reflectivity (representing hardness and softness) of substrates; and b) sediment grain-size analyses and video and photographic imagery that provide data used to interpret the features and patterns observed in the sonar imagery. In all, data from 420 stations were analyzed, including sediment samples from 325 locations. The geology-based maps show the distribution of 10 substrate types. A geologic substrate is characterized not just by sediment grain-size composition (mud, sand, gravel), but also by surficial features (for example, ripples), sediment layering (for example, finer sediment partly covering coarser sediment), sediment movement, and water depth range. The methodology employed to delineate substrates is explained in the accompanying report. 

Three maps in this series focus on regional physical characteristics of the seabed such as topography (Map A), ruggedness (Map B), and backscatter. Four interpretive maps show the distribution of: geologic substrates, which range from boulder ridges to mobile, rippled, coarse-grained sand to immobile, muddy, fine-grained sand; substrate mobility; substrates dominated by fine- or coarse-grained sand; and substrate mud content. 

The purpose of the map series is to provide a range of information about the distribution of physical attributes of the seabed at a scale of 1:25,000 (1 cm on the map represents 250 m on the seabed) that is justified by the density of data. High-resolution information will serve as a foundation for study of sediment transport and the ecology of vertebrate and invertebrate species that use these substrates as habitat, and for planning and managing development of this offshore region. 

The maps were conceived and compiled by Page Valentine, Leslie Gallea, and VeeAnn Cross, all of the USGS Woods Hole Coastal and Marine Science Center, Woods Hole, Massachusetts. 

View all of the maps here: Seabed maps of Stellwagen Bank

The full citation for the map series is: 

Valentine, P.C. and Gallea, L.B., 2015, Seabed maps showing topography, ruggedness, backscatter intensity, sediment mobility, and the distribution of geologic substrates in quadrangle 6 of the Stellwagen Bank National Marine Sanctuary region offshore of Boston, Massachusetts: U.S. Geological Survey Scientific Investigations Map 3341, 10 sheets, scale 1:25,000, and 21-p. pamphlet, http://dx.doi.org/10.3133/sim3341