USA (North-East) - Environment

The four NEUS regions: Gulf of Maine (GOM), Georges Bank (GB), Southern New England (SNE), and the Mid-Atlantic Bight (MAB) are connected and are in many respects over-lapping, but have distinct enough physio-chemical, geological, bathymetric and biological properties to merit their differentiation as separate sub-regions.
In general terms, the circulation in this ecosystem is predominantly from northeast to southwest. Water enters the Gulf of Maine from the Scotian Shelf and from the Northeast Channel. This flow travels counterclockwise around the Gulf. Some exits through the Great South Channel, while the remainder flows eastward along the northern flank of Georges Bank. This eastward flow contributes to the anti-cyclonic circulation on Georges Bank, with some of this flow recirculating at the Great South Channel, while some continues southwestward along the remainder of the northeast U.S. shelf. Tidal-scale forcing is also an important component of the physical dynamics, with the shallower portions of Georges Bank remaining well mixed even during periods of stratification over the deeper portions of Georges Bank and the Gulf of Maine. Flows onto and alongshore the Mid Atlantic Bight (the region south of Gulf of Maine and Georges Bank) have had some drastic effects on water mass properties, as has the changing influence of Labrador slope and Scotian Shelf waters into the Gulf of Maine (Mountain, pers. comm.; Drinkwater and Mountain, 1997). From a basin-scale oceanographic point of view, the Gulf Stream separates from the shelf edge at Cape Hatteras, contributing to two very different water masses north and south of the Cape, notably on and off the continental shelf. At the northern extreme, the Gulf of St. Lawrence provides another oceanographic boundary as the cold, relatively fresh water from the St Lawrence River effectively blocks movement onto the Newfoundland shelf. Both Sherman (2003) and Longhurst (1998) make similar distinctions in their definitions of large marine ecosystems using these oceanographic features in delineating Atlantic ecosystems. For more details about physical oceanographic factors, see Mountain (1989), Taylor and Bascunan (2001), and Brodziak and Link (2002).
Cold, fresher, Labrador slope waters enter the Gulf of Maine via the Northeast Channel, forming a counterclockwise gyre in that region. Georges Bank is shallower, bounded on the north by the afore-mentioned circulation pattern in the Gulf of Maine, and bounded on the south by warmer, more saline slope waters. Many of the same features as on Georges Bank extend westward into Southern New England waters, which are slightly deeper, have finer sediments (owing to reduced tidal mixing), and have a predominantly southwestern water flow pattern on the shelf. The Mid-Atlantic waters overlay a narrower continental shelf, are more heavily influenced by long-shore north-south circulations, and contain more sub-tropical biota than the other three sub-regions. Combined these circulation patterns serve to make the NEUS region highly productive.