Conceptual Model

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The waters in the GoM and the NSS are connected.  Relatively cold, low salinity Scotian Shelf Water (SSW) enters the GoM in the surface layers around Cape Sable and meets warmer and more saline slope water (called Warm Slope Water, WSW) that enters at depth through the Northeast Channel. The primary source of SSW is the West Greenland/Labrador Current system, with additional input from the St. Lawrence system (Houghton and Fairbanks, 2001, Fratantoni and Pickart, 2007).  These two waters progressively mix as they move in a general counter-clockwise pattern around the GoM, and then turn clockwise around GB with the major portion of the flow continuing westward into the Mid-Atlantic Bight (Beardsley et al., 1997, Wiebe et al., 2002).  The variation of SSW inflow, influenced by large-scale freshening, may alter water properties and stratification patterns as illustrated in Figure 1.  Enhanced inflow of low salinity SSW at the surface can stabilize the water column in the NSS region, and facilitate earlier spring phytoplankton blooms (SPBs) than that in the GoM region (where thermal stratification induced by heating occurs later in the year), causing an apparent westward propagation of blooms.  On the other hand, enhanced SSW inflow might reduce the overall productivity in the GoM, since decreased surface salinity can impede winter convection and result in a weak exchange between surface and deep waters (Taylor and Mountain, 2008), lowering nutrient concentrations available for phytoplankton growth in surface water during springtime.  As a result, the duration of SPBs may be shortened and the post-bloom productivity decreased.  The influence of freshening is expected to be more prominent in the NSS and the eastern GoM region than that in the western GoM, since the intensity of freshening can be significantly attenuated westward by increased mixing of surface water with high-salinity deep water in the Gulf. 


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Last updated July 10, 2008
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