HYDROGRA^PHY OF THE MARINE WATERS 21 



must be the agent molding this coastline. Johnson (1919, 1938) discusses cer- 

 tain types of normal wave action and the influence of prominences of the 

 inner shoreline as alternative explanations for this cuspate coast. 



Comparing these factors influencing the coastal currents off North Caro- 

 lina, it is obvious that tidal effects are small and tend to cancel out because 

 of their rotary nature. The non-tidal currents for representative months, as 

 shown in Figure 4, are essentially the over-all resultant of (i) wind currents, 

 (2) whatever Florida Current influence there might be, and (3) a variety of 

 minor influences. The Florida Current influence is more or less direct and 

 strong at the Diamond Shoal station, of course, whereas at Cape Lookout and 

 Frying Pan Shoals it is indirect. That the resultants at the latter stations are 

 compatible with Abbe's (1895) concept (Figure 5) and not with the wind 

 roses of Figure 26 seems to indicate a weak, variable back-eddy circulation 

 repeatedly modified by winds, tides, etc. 



According to Bigelow (1933), and Bigelow and Sears (1935), there is 

 nothing to indicate that waters from the Hatteras region and southward 

 move in appreciable quantities into the coastal waters off the Middle Atlantic 

 States. Whether there are frequent or occasional southward invasions of the 

 latter waters has not received appreciable attention, but I have found nothing 

 in the literature to suggest such a coastal influence from the north. 



Temperatures Offshore 



The Hatteras region has long been referred to as a temperature barrier to 

 the distribution of marine forms; however, as coastal temperature gradients 

 and information on actual distribution are analyzed, it is learned that this 

 region is not only a barrier but is also a wintering area for migratory popula- 

 tions, and even, to some extent, a center of dispersal. The fisheries poten- 

 tialities suggested by these unusual temperature influences merit considerable 

 study, as is suggested, for example, by the large wintering populations that 

 have been discovered in the last two decades by trawlers working off southern 

 Virginia and North Carolina. 



The most complete temperature records for our Atlantic coast are the 

 surface temperatures taken at lightships and at lighthouses on the ocean 

 shore. These were first taken during the years 1881-85 and were analyzed by 

 Rathbun (1887). Later Parr (1933) analyzed records for 1928-30, included 

 selections from Rathbun's publication for comparison, and elaborated exten- 

 sively on the ecological significance of this temperature information. 



Such continued records adequate for a discussion of the coastwise tempera- 

 ture cycle are surface records only; consequently, it is important to consider 

 the depth to which these apply in continental shelf waters. Parr (1933) has 



