Northern Coastal Shelf

Overview
Ranging from Cape Ann in the western Gulf of Maine to the Bay of Fundy in the east, the Northern Coastal Shelf encompasses a heterogeneous variety of habitat types and bathymetry. The coast is incised with a great variety of embayments and estuaries; intertidal areas are characterized by sand beaches, mudflats, saltmarshes and rocky shores. Like other shallow areas of the Gulf, where tidal action provides a steady supply of nutrients to well lit surface waters, the Northern Coastal Shelf is highly productive. Once supporting fisheries for groundfish, lobster, herring, and other species, the Northern Coastal Shelf is now dominated by lobster fishing. Coastal development has resulted in habitat destruction and pollution.1

Surface area
5,699 mi2

Depth
Intertidal zone to ~100 m

Bathymetry including key features
The bathymetry of the nearshore reflects in many cases the topography of the adjacent shoreline: bedrock peninsulas extend underwater as bedrock features, sandy beaches are matched underwater by gently sloping areas, waters offshore of cliffs reach steep depths quickly, and marshes and mud flats are mirrored by subtidal deposits of fine sediments.2

Jeffrey’s Ledge is a glacial deposit that forms a curving shoal 33 miles long at the western terminus of the Northern Coastal Shelf. From 40-70 m deep, the topography of Jeffrey’s Ledge creates an upwelling zone that attracts a wide variety of marine life.3,4

Substrate
Substrate in this area of the Gulf of Maine is extremely heterogeneous; it includes bedrock, sand, gravel, silt and mud, and an almost infinite range of combinations, occurring at a variety of scales. Sixty meters marks the point of lowest sea level since the last ice age. The passage of sea level through this depth range removed many of the unconsolidated sediments; as a result, bedrock predominates in much of the shallow waters of the Northern Coastal Shelf.5

Relationship to large-scale circulatory patterns of the Gulf of Maine
The oceanography of the Northern Coastal Shelf is dominated by coastal currents that flow southwesterly along the coast. These currents are a component of the counterclockwise gyre that dominates gulf-scale circulation.6,7

Information on average (seasonal/annual) oceanographic conditions
The spring freshet strengthens the coastal current in April through June and results in a decrease in salinity. The eastern portion of this current is relatively fast moving and somewhat colder than the western portion of the current. Where the two meet, at the mouth of Penobscot Bay, the faster moving eastern current is, to a large degree, deflected offshore. The portion of the current that is not deflected flows through to the west. The amount of flow through varies from year to year. The western coastal current reverses for a brief period every spring, sometimes weakly and directed offshore, sometimes strongly and in a northeasterly direction.8,9

Due to the shallow nature of the coastal shelf, the water column in this area is well mixed by tidal action. The coastal shelf is separated from the stratified interior of the Gulf by a tidal front.10

Presence of GoMOOS buoy
Five GoMOOS buoys are deployed along the Northern Coastal Shelf. They include buoys B, C, E, F, and I.

1 Woodward, 2004
2 Dorsey and Pederson, 1998
3 Whale Center of New England, Undated
4 Blue Ocean Society for Marine Conservation, Undated
5 Dorsey and Pederson, 1998
6 Pettigrew, et al., In Press
7 Xue, et al. 2000
8 Pettigrew, et al., In Press
9 Xue, et al., 2000
10 Xue, et al., 2000