HIGH RESOLUTION MAPPING OF MORPHOLOGIC FEATURES AND SEAFLOOR SEDIMENTS OF THE NEW HAMPSHIRE AND VICINITY CONTINENTAL SHELF, WESTERN GULF OF MAINE

The Western Gulf of Maine (WGOM) seafloor is extremely complex with extensive bedrock outcrops, marine modified glacial deposits, marine formed shoals, and muddy offshore basins. Many of the depositional features found on the shelf are dominated by remnant glacial features (e.g., drumlins, eskers, moraines) that were significantly modified by marine processes as sea-level fluctuated following deglaciation. The glacial deposits were eroded, leaving very coarse lag deposits, while supplying sand and fine gravel to develop wave formed features (shoals). A number of the nearshore glacial and other physiographic features found on the shelf continue onshore. As a result, the New Hampshire continental shelf’s morphologic features and sediment are highly diverse and vary significantly over short distances.

Over the last decade, the geology (primarily morphology, depositional systems, and controlling processes) of the New Hampshire and vicinity continental shelf has been extensively studied based on archived databases (subbottom seismics, vibracores and surficial sediments), as well as more recently available high resolution multibeam echosounder (MBES) bathymetry and backscatter. In addition, field campaigns were conducted in 2016-2017 to obtain additional ground truth (bottom sediment samples and videography). From this database, high resolution seafloor maps were developed using various seafloor classifications, but primarily the Coastal and Marine Ecological Classification Standard (CMECS). Although much of the mapping effort ultimately relies on human interpretation or expert opinion, new approaches using acoustics are being evaluated such as BRESS (Bathymetry- and Reflectivity-Based Estimator for Seafloor Segmentation: see Masetti et al. 2018). The overall mapping effort is focusing on morphologic features (geoforms), classification of the grain size of surficial sediment, and description of selected sand and gravel deposits. The new surficial geology maps represent a major advance in our efforts to understand and characterize the New Hampshire and vicinity continental shelf.

Masetti, G., L.A. Mayer and L.G. Ward. 2018. A bathymetry- and reflectivity-based approach for seafloor segmentation. Geosciences:8,14. doi:10.3390/geosciences8010014.