THEORETICAL CONSIDERATIONS 



Based on the liraited number of observations available throiigh this 

 and previous studies in the vicinity of Plantagenet Bank, it is perhaps 

 reasonable to speculate as to possible mechanisms of current flow 

 which may exist in this region. Theoretical considerations of the mod- 

 ifications which should occur to a surface current impinging on the 

 Bank are simplified by regarding the current system as being comprised 

 of two discrete regimes in which quite dissimilar mechanisms are oper- 

 ative. These seemingly obvious categories of flow in the immediate 

 proximity of the Bank are: (l) flow over the Bank and (2) flow around 

 the Bank. 



The first category involves a surface deflection which is analogous 

 to the frictional deflection of currents passing over a submarine ridge 

 (Figure 8). In accordance with theory, a current moving over the up- 

 slope portion of the seamount is deflected toward the right; after 

 passing over the seamount and while over the downslope portion, the 

 current is theoretically deflected toward the left and thus may approxi- 

 mately resume its original direction. Such an influence would imply 

 that impinging currents were in a more easterly direction prior to being 

 deflected than the southeasterly flow observed over the Bank. It is 

 possible that this hypothetical easterly direction is resumed by currents 

 after passing over the Bank. 



The second category involves flow around either side of the sea- 

 mount similar to that experienced around a submerged cylinder (Lamb, 

 19^5) at depths below the upper surface of the Bank (Figiire 9). Super- 

 imposed upon these two mechanisms is an upward component of current flow 

 caused by movement of the impinging current up the leading face of the 

 seamount. Thus it is theorized that lateral spreading should occur in 

 a manner similar to conditions discussed by Neumann (19^0) and Wust (19^0) 

 in the vicinity of Altair Dome near the Azores. The existence of a rather 

 large eddy regime on the lee side of the Bank must also be considered a 

 distinct possibility. 



These concepts have been incorporated into two grossly simplified 

 models (Figures 8 and 9) v;hich serve to illustrate theoretical current 

 patterns which may have existed during the period of observation. 



CONCLUSIONS 



Based on these observations, the following characteristics of the 

 ocean currents over Plantagenet Bank during the period of study (1-15 

 August 1961) are apparent: 



1. Currents were primarily southeasterly with speeds ranging from 

 to 1.4 knots. Average speed was 0.^5 knot. 



2, The current was observed to be relatively constant in both 

 speed and direction at all locations on the Bank except at the extreme 



