Western Gulf of Maine Surficial Geology and Sediment Database

New Hampshire and Northern Massachusetts Coast to Jeffreys Ledge

CONTACTS
Larry Ward and Rachel Morrison

DISCLAIMER
All information provided here is for displaying seafloor properties and cannot be used for navigation purposes.

Full Report
Ward, L.G., Morrison, R.C., Bogonko, M., and Johnson, P., 2026, Western Gulf of Maine Surficial Geology: New Hampshire and Northern Massachusetts Coast to Jeffreys Ledge. University of New Hampshire Center for Coastal and Ocean Mapping and Joint Hydrographic Center (CCOM/JHC) Technical Report, 25 Colovos Road, Durham, NH 03824. DOI: ????????

(Access the Interactive Compilation Button)

Overview

The Western Gulf of Maine (WGOM) has been shaped by the interactions of marine processes, riverine sediment input, sea-level fluctuations, and multiple glaciations during the Quaternary period—which dramatically altered the landscape. Consequently, the seafloor is extremely complex with bathymetric highs, muddy basins, sandy shoals, exposed bedrock, cobble boulder complexes, and extensive marine-modified glacial deposits including drumlins, eskers, and deltas (Figure 1).

Over the last decade, the University of New Hampshire (UNH) Center for Coastal and Ocean Mapping (CCOM) conducted numerous studies in the WGOM focused on seafloor characterization, surficial geology mapping, and assessing potential sand and gravel resources. This work led to the development of high-resolution surficial geology maps of the continental shelf off northern Massachusetts, New Hampshire, and southern Maine coasts seaward to Jeffreys Ledge (Figures 2–8; Ward et al., 2026a). The seafloor geoforms (physiographic features) and substrate sediment were classified and mapped based on a modification of the Coastal and Marine Ecological Classification Standard (CMECS) developed by NOAA Integrated Ocean and Coastal Mapping (IOCM) (FCDC, 2012). The CMECS geologic substrate classification was used to describe seafloor geology due to its adaptability to different databases and use across multiple disciplines. CMECS is especially well-suited for developing surficial geology maps in complex environments such as the WGOM.

The surficial geology from Portsmouth Harbor to the Merrimack River was previously mapped by CCOM in 2015 and 2020 (Ward et al., 2016; 2021). The need to update and expand the maps was driven by several factors. First, major changes were made to CMECS in 2023 to improve upon the original (2012) substrate sediment classification scheme and to facilitate greater detail within the class, subclass, and group categories (NOAA OCM, 2026). CCOM participated in the working group tasked with revising these classifications. At the same time, CCOM modified the CMECS geoform classification to better describe physiographic features in paraglacial environments such as the WGOM (Table 2). Secondly, substantial new high-resolution bathymetry and backscatter surveys became available in the Gulf of Maine after 2020 (Ward et al., 2026b), which enhanced the ability to identify small-scale features and distinguish between sediment types. Lastly, expansion of the ground truth database through an extensive field campaign carried out in 2022-2023 by CCOM allowed verification of previously unmapped areas.

The surficial maps increase the coverage by ~85% over previous surveys and extend from approximately Portsmouth Harbor to Cape Ann and seaward to Jeffreys Ledge, covering a total area of ~3,230 km² (Figure 1). Also available here is the extensive database used for the surficial geology mapping which includes sediment grain size, seafloor photographs, and vibracores.

Map Products

Presented here are the WGOM surficial geology maps based on CMECS showing the sediment size classifications and geoforms in varying levels of detail. CMECS is built on a broadening of the Wentworth (1922) and Folk (1954; 1980) grain size schemes. Size classes are grouped into a hierarchy of categories including Substrate Class, Substrate Subclass, Substrate Group, and Substrate Subgroup (Table 1). The broadest level (“class”) has three categories (consolidated mineral seafloor, coarse unconsolidated substrate, and fine unconsolidated substrate) (Figure 2). When other data sources are available such as ground truth samples, high-resolution bathymetry, and backscatter surveys, the mapping resolution and accuracy can be increased. Substrate class can then be further refined to “subclass” (Figure 3), then to substrate “group” (Figure 4), and finally to the highest order mapping at the substrate “subgroup” level with 30 classes (Figure 5). Examples of the difference in detail between the substrate class and subgroup (fewest categories to most categories) are shown in Figure 6.

Experience from CCOM’s earlier surficial geology mapping in the WGOM also showed the need to adapt the CMECS geoform classifications for paraglacial environments. Therefore, presented and used here are modifications of the CMECS geoform definitions and additional new features. The new geoforms and geoform types are presented in Table 2 and Figures 7 and 8.

Detailed descriptions and tables showing all substrate classifications and geoform terminology are available in Ward et al. (2026a) and its appendices.

Bathymetric map of WGOM with outline of surficial geology map area.

Figure 1. Location map showing some of the major geographic features in the Gulf of Maine, and the outline of new surficial geology maps extent (red dashed line). Scale is 1:900,000.

Color- coded surficial geology of WGOM continental shelf.

Figure 2. Surficial sediment map of the WGOM continental shelf classified using the CMECS substrate class. Scale is 1:270,000.

Figure 3. Surficial sediment map of the WGOM continental shelf classified using the CMECS substrate subclass. Scale is 1:270,000.

Figure 4. Surficial sediment map of the WGOM continental shelf classified using the CMECS substrate group. Scale is 1:270,000.

Figure 5. Surficial sediment map of the WGOM continental shelf classified using the CMECS substrate subgroup. Scale is 1:270,000.

6 images showing select areas of substrate in GOM

Figure 6. Selected areas showing the CMECS substrate class (least detailed with 3 categories; left) compared to the substrate subgroup (most detailed with 19 categories; right). The top figures are from near the Isles of Shoals, the middle figures are from Portsmouth Harbor, and the bottom figures are from Jeffreys Ledge.

Color-coded map showing geoforms in the WGOM with color key below.

Figure 7. Surficial geology map of the WGOM continental shelf showing major physiographic features based on a modification by CCOM of the CMECS geoform classification for paraglacial environments. Scale is 1:270,000.

Figure 8. Surficial geology map of the WGOM continental shelf showing major physiographic features based on a modification by CCOM of the CMECS geoform type classification for paraglacial environments. Geoform types provide more detail than geoform maps. Scale is 1:270,000.

Table showing Coastal and Marine Ecological Classification Standards

Table 1. Coastal and Marine Ecological Classification Standard (CMECS) updated classification system from 2023 (NOAA OCM, 2026). See Ward et al. (2026a) for complete category descriptions.

Green and White table of CMECS geoform categories as modified by CCOM for use in paraglacial environments.

Table 2. CMECS geoform categories as modified by CCOM for use in paraglacial environments. See Ward et al. (2026a) for complete definitions of categories.

Interactive Database and Sources

The WGOM surficial geology maps were built from the following resources.

High-resolution bathymetry and topography compilations: composed of multibeam echosounder bathymetry (MBES) and bathymetric lidar for the offshore, and high-resolution topographic lidar for the onshore region. Both gridded at 4m (Figure 9). See “Gulf of Maine Bathymetry, Backscatter, and Coastal Topography” for details (Ward et al., 2026b) and associated CCOM webpage: https://www.ccom.unh.edu/gulf-maine-bathymetry-backscatter-coastal-topography
Regional bathymetry compilation: lower resolution bathymetry extracted from the GMRT (Global Multi-Resolution Topography grid: GMRT v4.4.0; Ryan et al., 2009) and compiled with the high-resolution compilation to fill gaps in MBES coverage. Gridded at 16m (Figure 10). See “Gulf of Maine Bathymetry, Backscatter, and Coastal Topography” (source shown above).
MBES backscatter surveys and syntheses: based on 112 individual backscatter surveys (Figure 10) and two previously published mosaics. See “Gulf of Maine Bathymetry, Backscatter, and Coastal Topography” (source shown above).
CCOM Western Gulf of Maine sediment and photograph database: composed of 1,033 bottom sediment grain size samples, 1,290 seafloor photographs, and 23 vibracores (Figure 11). See Ward et al. (2026a) for details on original databases and associated interactive database available on CCOM website: XXXXXXXXXXXXXXXXXXXXXXXXXX??
USGS sediment and photograph databases (see Ward et al., 2026a for original sources).

GOM hi-res bathy and topographic compilation maps

Figure 9. Gulf of Maine high-resolution bathymetry and topography compilation maps (gridding 4m; scale 1:2,200,000). See Ward et al. (2026b) for survey metadata.

Figure 10. Individual MBES backscatter surveys in the GOM shown on top of the regional bathymetry compilation. The surveys were identified during a thorough review of MBES surveys. As is apparent, not all past MBES surveys used for the high-resolution bathymetry compilation had usable backscatter. See Ward et al. (2026b) for footprints and metadata for the backscatter surveys shown here. Map scale is 1:1,600,000.

Bathymetric map of NE coast with dots representing ground truth sites

Figure 11. UNH ground truth station locations. Data includes all sediment data collected between 1971 and 2024 (Ward et al., 2026a). Surface sediment locations are represented by the dark blue dots, seafloor photographs are in light blue, and vibracores are in red. Scale is 1:250,000.

Summary

High-resolution surficial geology mapping in complex paraglacial environments such as the Western Gulf of Maine requires detailed knowledge of seafloor morphology and substrate. To meet this requirement, multibeam echosounder bathymetry (MBES) from the Gulf of Maine and bathymetric lidar datasets from the nearshore were compiled and gridded at 4m; MBES backscatter datasets, where available, were used for identifying textural boundaries between coarse and fine sediments; and extensive ground truth was used to verify surficial geology classifications. The Coastal and Marine Ecological Classification Standard (CMECS) was applied to identify and map seafloor geoforms (physiographic features) and substrate sediment because of its applicability to interdisciplinary studies and adaptability to a range of supporting data quality. Collectively, the database supported the development of high-resolution surficial maps covering ~3,230 km² in the WGOM, revealing extensive bedrock outcrops, marine-modified glacial deposits, cobble boulder complexes, deep muddy shelf basins, sand shoals, and fluvial deposits.

The maps and the supporting databases should be viewed using the University of New Hampshire Center for Coastal and Ocean Mapping and Joint Hydrographic Center GIS Portal which allows for interactive viewing of the maps and database.

Reference List

FGDC (Federal Geographic Data Committee, Marine and Coastal Spatial Data Subcommittee), 2012, Coastal and Marine Ecological Classification Standard: FGDC-STD-018-2012, Washington, DC, 343 pp. https://www.fgdc.gov/standards/projects/cmecs-folder/CMECS_Version_06-2012_FINAL.pdf

Folk, R.L., 1954, The distinction between grain size and mineral composition in sedimentary-rock nomenclature: The Journal of Geology, vol. 62, number 4, pp. 344-359. https://doi.org/10.1086/626171

Folk, R.L., 1980, Petrology of sedimentary rocks: Hemphill Publishing Company, Austin, TX. 182 pp. Accessed May 2019, available online at https://repositories.lib.utexas.edu/handle/2152/22930

NOAA Office for Coastal Management, 2026, Coastal and Marine Ecological Classification Standard (CMECS) Catalog (Version 1.1.2) [Dataset]. US National Oceanic and Atmospheric Administration (NOAA) Office for Coastal Management (OCM). https://doi.org/10.5281/zenodo.21341526

Ryan, W. B. F., et al. (2009), Global Multi-Resolution Topography synthesis, Geochem. Geophys. Geosyst., 10, Q03014. https://doi.org/10.1029/2008GC002332

Ward, L.G., Vallee-Anziani, M., and McAvoy, Z.S., 2016, New Hampshire and vicinity continental shelf: Morphologic features and surficial sediments: BOEM/New Hampshire Cooperative Agreement (Contract M14ACOOO10) Technical Report, BOEM Marine Minerals Branch, Department of Interior, Bureau of Ocean Energy Management, Marine Minerals Division, 45600 Woodland Road, Sterling, VA, 20166, 24 pp.

Ward, L.G., McAvoy, Z.S., Vallee-Anziani, M., and Morrison, R.C., 2021, Surficial Geology of the Continental Shelf off New Hampshire: Morphologic Features and Surficial Sediment: BOEM/New Hampshire Cooperative Agreement (Contract M14ACOOO10) Technical Report. https://dx.doi.org/10.34051/p/2021.31

Ward, L.G., Morrison, R.C., Bogonko, M., and Johnson, P., 2026a, Western Gulf of Maine Surficial Geology and Sediment Database: Inner Shelf to Jeffreys Ledge. University of New Hampshire Center for Coastal and Ocean Mapping and Joint Hydrographic Center (CCOM/JHC) Technical Report, 25 Colovos Road, Durham, NH 03824.

Ward, L.G., Morrison, R.C., Bogonko, M., and Johnson, P., 2026b, Gulf of Maine Bathymetry, Backscatter, and Coastal Topography. University of New Hampshire Center for Coastal and Ocean Mapping, Technical Report, 25 Colovos Road, Durham, NH 03824, 41 pp.

Wentworth, C., 1922, A scale of grade and class terms for clastic sediments: The Journal of Geology, v. 30, no. 5, pp. 377–392. Accessed May 2019. https://www.jstor.org/stable/30063207

Use of Maps and Database

The information provided here is freely available for use. However, the University of New Hampshire (UNH) Joint Hydrographic Center/Center for Coastal and Ocean Mapping (JHC/CCOM) should be acknowledged for the surficial geology maps and data.

Recommended Web Citation

Ward, L.G., Morrison, R.C., Bogonko, M., and Johnson, P., 2026, Western Gulf of Maine Surficial Geology and Sediment Database: Inner Shelf to Jeffreys Ledge, University of New Hampshire Center for Coastal and Ocean Mapping, Durham. https://www.ccom.unh.edu/western-gulf-maine-surficial-geology-sediment-…

Use the CCOM Bathymetry Downloader Tool available on the UNH/CCOM-JHC GIS Portal to download data layers.

Map Coordinate System, Projection and Datum

Coordinate System: WGS 1984 UTM Zone 19N
Projection: Transverse Mercator
Vertical Datum: MLLW (bathymetry); NAVD88 (topography)

Acknowledgements

The development of the “Western Gulf of Maine Surficial Geology and Sediment Database: Inner Shelf to Jeffreys Ledge” maps, web serving, and report was supported by the University of New Hampshire/National Oceanic and Atmospheric Administration Joint Hydrographic Center Award Number NA20NOS4000196.