The Gulf of Maine is a "sea within a sea", part of the Atlantic Ocean that stretches from Cape Cod Bay off Massachusetts to the Bay of Fundy between New Brunswick and Nova Scotia. The outer edge of the Gulf is separated from the open ocean by a series of shallow areas known as Banks. Only one deep channel connects the Gulf to the open Atlantic, the Northeast Channel. The cold Labrador current and the warm Gulf Stream current rarely flow into the Gulf; both are blocked by the banks, the current motion in the Gulf's waters, and the Earth's rotation.
George's Bank is the largest and most famous bank. Its average depth is 195 feet, but parts of it are less than 12 feet deep. The George's Bank Region helps to make the Gulf of Maine one of the world's most productive water bodies, supporting a large number of species. A large quantity of living material is present in the Gulf, called Biomass. This biomass mostly in the form of phytoplankton floating in the water, actually gives the Gulf of Maine its characteristic emerald green color. This phytoplankton forms the base of the Gulf's food chain on which hundreds of species of plants and animals rely.
The productivity of the Gulf is enhanced by huge volumes of freshwater that flow into the Gulf from four major rivers (the Kennebec, Androscoggin, Penobscot and St. John), as well as a host of smaller ones ( the Saco, Piscataqua, Merrimac and St. Croix). This inflow of freshwater, which is particularly heavy during the spring when the snow pack melts, dilutes the salinity of the sea water;warms the surface waters; and adds nutrients, minerals, sediments and pollutants to the Gulf.
As the freshwater reaches the Gulf, it is thrown westward by the Earth's rotation. The large volume flowing in to the Gulf causes the surface water to move in a huge counterclockwise spiral. This motion decreases after the heavy spring runoff, but never completely disappears. Tidal currents and gravity currents maintain the circulation, which helps to distribute nutrients. Nutrients are also circulated by upwelling, a process in which colder, denser, more fertile waters from the ocean floor are drawn to the Gulf's surface. Upwelling is fueled by currents, tides, local weather and the topography of the ocean floor.
