Geoscience Reference
In-Depth Information
Yachts rest at anchor at Marblehead, Massachusetts, while cormorants enjoy a pierside perch.
Although apparently open to the sea, the Gulf of Maine is a marginal sea unto itself, largely cut off from the
Northwest Atlantic by two fish-rich banks, Georges, which extends like a giant thumb off the outstretched arm
of Cape Cod, and Browns, which lies off the southwestern tip of Nova Scotia. In essence, these banks are great
sand dunes that were formed as outwash from the retreating glaciers, and today they rise from the ocean bot-
tom to within a few tens of meters of the wave tops.
Two currents dominate the water circulation within this marginal sea: a counterclockwise gyre in the Gulf
and an adjacent clockwise gyre on Georges Bank. The Nova Scotia Current, which is a cold offshoot of the
Labrador Current, enters the Gulf of Maine through the Northeast Channel and is promptly deflected to the
north, into the Bay of Fundy, by the Earth's rotation (the Coriolis effect). It then describes a counterclockwise
gyre, skirting, in turn, the coastlines of New Brunswick, Maine, New Hampshire, and Massachusetts, before
the upturned arm of Cape Cod redirects its slow journey, which takes about three months to complete. At its
southern boundary, the current encounters the northern edge of Georges Bank. Some of the water skirts the
bank and continues on its counterclockwise journey, while the rest flows around the northeast peak, helping to
create the second gyre, which circles the bank in a clockwise direction. Water that does not complete the cir-
cuit of the bank spills into the North Atlantic through the Northeast Channel, or it may be lost through the
Great South Channel, near Nantucket Shoals, before flowing southward to the Mid-Atlantic.
This is a simplified picture of a very complex circulatory pattern that expresses itself in marked variations in
temperature, salinity, and nutrient content of the water, depending on the season, location, and water depth.
Critically, these currents, or gyres, together with tidal action, combine to produce conditions that are conducive
to life in the sea.
