Monitoring at MacMillan Wharf, Provincetown, MA

Monitoring at MacMillan Wharf, Provincetown, MA
Marine Invasive Species (MIS) Monitoring at MacMillan Wharf, Provincetown, MA.

Friday, August 31, 2012

The Gulf of Maine

Created by the Glaciers - Regulated by its Currents

The Gulf of Maine is a large body of water in the Northwest Atlantic Ocean between Cape Cod, Massachusetts, and Cape Sable, Nova Scotia.  Cape Cod Bay, Massachusetts Bay, and the Bay of Fundy are all included within the Gulf.  The underwater features of the seabed were sculptured during the last ice ages 25,000 years ago when  sea levels were lower.  Glaciers scoured the earth and deposited rocks and rubble creating the current Northeast American landmass and several underwater banks (Georges, Browns, Jeffreys, and Stellwagen).  The Gulf is a semi-enclosed sea bounded to the south by Georges Bank and to the east by Browns Bank.  The coastline north of Boston is predominantly rocky due to the effects of glaciation, which stripped sedimentary soil away.  Georges and Browns Banks separate the Gulf from the warmer waters of the Gulf Stream.   Gulf of Maine waters are more strongly influenced by the Nova Scotia and Labrador Currents, making the Gulf waters significantly colder and more nutrient-rich than those found to the south.
Bottom Topography of the Gulf of Maine 
Bottom Topography of the Gulf of Maine.  The outer banks enclose several basins and shallow banks that were formed during the advance and retreat of the glaciers.  The Stellwagen Bank is probably an underwater extension of Cape Cod, is the site of the Stellwagen Bank National Marine Sanctuary, and is famous for whale watching.
Temperatures in the West Atlantic showing effect of the Gulf Stream
 The Gulf Stream brings warm water from the Caribbean north (red) along the Florida Coast and moves off the coast at Cape Hatteras.   In the summer, eddies and meanders from the Gulf Stream bring warm waters to the mid-Atlantic States and Long Island.  The Labrador Current brings cold water south from Nova Scotia to the Gulf of Maine.  Massachusetts and Cape Cod Bays form a transitional region between colder waters to the north and warmer waters from the Gulf Stream.

Sea Surface Temperatures Along the North American Coast 
Winter and Summer sea surface temperatures along the mid-Atlantic coast and in the Gulf of Maine.  In the winter, the Labrador Current pushes the warm waters from the Gulf Stream south and away from the Northeast coast.  In the summer, warm waters move north towards the Mid-Atlantic States, but the Gulf of Maine remains cooler due to water flowing south from Nova Scotia into the Gulf.
Currents in the Gulf of Maine
Within the Gulf, circulation is strongly influenced by the Nova Scotia Current which brings nutrient-rich waters through the Northeast Channel. This current helps drive the primarily counterclockwise circulation of the Gulf which brings cooler water from Maine to Massachusetts. The main currents circulate around the basins, allowing shallow waters along the coast and in Cape Cod Bay to warm up during the summer.  The currents are also influenced by fluctuations in river outflow, often enhanced during spring runoff, and by huge tides (over 10 feet in Provincetown).  Tidal variation increases in a northeast direction along the coastsline reaching a maximum in the Bay of Fundy with variations over 50 feet.
 Representative Salinity Levels in Massachusetts and Cape Cod Bays
Salinity in the Gulf of Maine.  Five-day averaged surface salinity (color) and currents (cm s−1) (arrows) during spring blood periods in 1998 and 2000.  Units given in parts per thousand.  Fresh water from rivers on the northeast MA coastline north of Cape Ann (upper dark blue area) and in Boston Harbor (lower dark blue area) reduce salinity levels at the source and locations south of the rivers (because of water currents in the Gulf of Maine, see above).  The outer Cape, including Provincetown, are less affected by rivers because the watershed is limited and large tidal variations recirculate sea water in the marinas.
River Systems in Boston Harbor and Coastline North of Cape Ann 
Left, North of Cape Ann, the Merrimack River empties directly on the Coast.  The Parker and  Ipswich Rivers empty into Plum Island Sound whereas the Essex River drains into Essex Bay. 
Right, in Boston Harbor, the Charles and Mystic Rivers empty into the north harbor, the Neponset River joins the mid-harbor at Quincy, and in the south harbor, the Weymouth Fore and Back Rivers empty into Hingham Harbor.