the volume of MIW diminishes as it mixes with waters above and below it, 

 especially as it leaves the Gulf of Maine via the Northeast Channel and the 

 Great South Channel. 



Bigelow (1933) labeled a cool, low-saline water mass found in the lower layer 

 at the shelf edge of the Mid-Atlantic Bight as the "cold pool." He identified 

 it as remnant winter water. More recent observations (e.g., Beardsley et al. 

 1976) have shown the cold pool to be moving to the southwest along bathymetric 

 contours. Such a movement implies an upstream source and various 

 possibilities have been suggested, among them the Gulf of Maine. Thus, MIW 

 potentially may be a source for the subthermocline waters of the Mid-Atlantic 

 Bight. The band of cooler water covers a large portion of the benthic regime. 

 The exposure is roughly proportional to the vertical thickness of MIW, which 

 may vary from zero to >50 m of any cross section. The geographic distribution 

 of certain demersal fish stocks is influenced by annual trends in temperature 

 (see chapter 11, "Fishes"). Colton (1972) has given evidence that detectable 

 southward shifts occurred for the distribution of American plaice and 

 butterfish associated with the cooling trend between 1952 and 1967. The 37 to 

 45 °F (3 to 7 °C) thermal bank of MIW coincides with the optimal spawning 

 temperatures for stocks such as plaice and haddock; and since this range 

 differs by several degrees from that of MSW, or even MBW, local variations in 

 MIW availability could represent significant differences in thermal regulation 

 of the duration of spawning populations. Similar relationships with other 

 fish and shellfish have not been investigated but undoubtedly occur. Lack of 

 nearshore hydrographic data prevents analysis of the role of MIW in coastal 

 marine waters. For the same reason the nearshore seasonal distribution of MIW 

 cannot be determined. 



MIW has the potential to provide nutrients to the coastal zone. This is 

 covered in "Nutrients," in chapter 5. This interaction is one of the major 

 physical forcing functions in coastal Maine. 



Tides. Tide, or the periodic rise and fall of the ocean, and 

 accompanying tidal currents are caused by the gravitational effect of the moon 

 and sun on the ocean. Observed tides are primarily the response to the 

 greater attractive force of the moon. Tides vary in height during the month. 

 Tidal terms are defined in table 4-3 and illustrated in figure 4-7. Tidal 

 level and range are important in determining the location, quantity, and type 

 of flora and fauna inhabiting the intertidal zone (see "Intertidal Subsystem," 

 below) . Tidal level is also important in predicting dispersal of pollutants 

 (e.g., oil) in the intertidal zone. For example, an oil spill could impact 

 higher tidal levels and a greater area during a spring tide than during a neap 

 tide. 



Because of the configuration of the Bay of Fundy, the tide in the Gulf of 

 Maine and the Bay of Fundy assumes some characteristics of a standing wave. 

 Two important consequences of this phenomenon are that the time at which the 

 tide "turns" is nearly simultaneous along the outer coast and the range of the 

 tide increases from west to east as the Bay of Fundy is approached. At 

 Portland the mean tidal range is 9.0 feet (2.7 m) , while at Eastport the mean 

 tidal range is 18.2 feet (5.5 m) . More intertidal area is available for 

 colonization by organisms in areas of large tidal range. 



4-18 



