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Chapter 4 - Physical Oceanographyshelf. This current switches betweentwo modes of circulationthat are related to its positionrelative to the Continental Slope(Townsend et al. 2006). Whenthe Gulf Stream is positionedfarther offshore, it has more activemeanders that can split fromthe current as warm water eddies,known as warm core rings orfilaments, which are transportedonto the shelf (Townsend et al.2006). The Labrador Currentoriginates in the Arctic, where itis fed by Greenland ice melt andcontinental fresh water sources,giving it a cold, low salinity signature(Townsend et al. 2006). Itdiverges around the Grand Banks,and part of it becomes Labradorslope water that flows into theGulf of Maine and furthersouth to the Mid-Atlantic Bight(Longhurst 2007).Figure 4-1. Currents in the Northwest Atlantic region (reprinted with permission fromTownsend et al. 2006).Circulation PatternsLarge-scale currents transport larvae of numerous oceanicspecies and determine habitat connectivity at abroad scale (Shanks 1995). The broad, non-tidal circulationof the western Atlantic (Figure 4-1; Townsend etal. 2006) is dominated by two major current systems,the Gulf Stream and the Labrador Current. The GulfStream, characterized by relatively warm temperaturesand high salinities, flows northward past Cape Hatterasand turns to the east below the southern New EnglandThe Gulf of Maine is isolatedfrom the broader scale NorthAtlantic circulation by Brownsand Georges Banks (Townsendet al. 2006). Water enters theGulf of Maine primarily throughthe Northeast Channel that dividesthe two banks, and averagecirculation is counter-clockwisearound the Gulf (Townsend et al. 2006). The inner shelfregion of southern New England from Buzzards Bay toLong Island Sound is also semi-isolated by the presenceof land. Long Island Sound has an estuarine circulationpattern due to freshwater input (Townsend et al. 2006).Circulation on the inner shelf of the Mid-Atlantic Bightis also influenced by low density water from Delaware andChesapeake bays (Townsend et al. 2006). At the southernend of the region, very little water is exchanged past Cape4-Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report