N SUMMARY OF RESULTS 



Oil Spill Fates Model 



The oil spill fates model was used to simulate the 12 monthly spill cases 

 noted in table 1. Figures 3 and 4 show the trajectories of the surface slick 

 and subsurface hydrocarbon concentrations with time, noted in 5 day increments 

 from the start of the spill event, for the May and December spills respectively. 

 The other 10 monthly cases are documented in Spaulding, Saila et al . (1982). 

 The centers of mass of the surface slick and the 50 part per billion (ppb) 

 subsurface oil concentration contour are used to define the trajectories. An 

 outline of the coast and the 100 m and 1,000 m bathymetric contour lines have 

 been included to assist the reader in orienting the spill location to both land 

 and important shelf and basin bathymetry. Noted at the bottom of each figure 

 is detailed information on key spill parameters. 



An analysis of the 12 simulations shows differences in the response of the 

 surface and subsurface oil to the combined effects of the wind-induced and long- 

 term residual flow patterns drawn from a summary of drifter studies (Bumpus and 

 Lauzier, 1965). The surface spillets readily respond to wind forcing, while 

 the subsurface oil is more markedly influenced by the long-term advective field. 

 In overview, the subsurface oil trajectories are toward the southwest and west 

 in the fall and winter months, and become strongly influenced by the Georges 

 Bank gyre in the spring and summer. The trajectories of the surface spillets 

 are more convoluted than the subsurface trajectories because of their strong 

 response to the passage of weather events. Generally, surface spillets on 

 Georges Bank are transported to the southwest or southeast during the fall and 

 winter and toward the northeast from spring through early summer, following 

 the seasonal mean wind conditions. Stronger winter winds carry the surface oil 

 away from the spill site more rapidly than do the lower velocity late spring 

 and summer winds. 



It is interesting to note that when the wind speeds become more moderate, 

 such as in August, the surface spillet trajectories are affected by the transient 

 wind and residual flow in about equal magnitude. This observation suggests that 

 knowledge of the offshore residual current patterns is critical in determining 

 the trajectory of spilled oil in moderate weather, and indicates the need for 

 a proper hydrodynamic modeling effort to produce improved impact estimates. 



Table 2 presents the final mass balance in percent for each monthly spill 

 simulation, with the environment partitioned into atmosphere, sea surface, and 

 subsurface (water column) components. The first two columns show the mass and 

 volume of oil spilled. The last column, labeled "outside domain", indicates that 

 this percentage of the oil has left the study area by exiting through one of the 

 model boundaries. 



A review of the monthly oil spill final mass balances shows that 36.5 

 +0.5 percent is evaporated, 6+3 percent is in the water column and the 

 remaining 57+3 percent of the spilled oil is found on the sea surface. Based 

 on previous studies of mass balance for other oil spills (Spaulding, Saila, et 

 al . 1981) it is clear that the major structure of the final mass balance 

 relationships is determined by the oil type, with environmental factors such 

 as wind and temperature exhibiting only secondary roles. 



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