HYDROGRAPHY OF THE MARINE WATERS 23 



discussed this, both theoretically and on the basis of available evidence, and 

 has presented the following conclusions for the lightship and lighthouse 

 records: 



1. During the warm season surface temperatures may be considered 

 directly representative of conditions to a depth of at least 5 fathoms and 

 indirectly indicative of the stage of seasonal development of the entire 

 epithalassa, i.e., within at least the upper 10 fathoms of water. 



2. During the winter, surface temperature conditions generally represent 

 a layer of uniform temperature of about 10-50 fathoms depth. 



The second point is too conservative for the Hatteras region, which will be 

 the center of the present discussion, for here the surface temperatures are 

 indicative of conditions to the bottom. This is shown in Figure 6, a selected 

 illustration that agrees with other available data such as that tabulated by 

 Pearson (1932) and that which has been summarized and made available 

 by the Woods Hole Oceanographic Institution.^ 



Parr (1933) has also discussed his reasons for believing that records from 

 the Diamond Shoal Lightship, directly influenced by the Gulf Stream System, 

 apply to the narrow Cape Hatteras shelf area shoreward of this point. He has 

 written as follows: "... an elevated ridge less than five fathoms deep extends 

 outward nearly two-thirds of the way from Cape Hatteras to Diamond Shoals 

 Lightship, with a complex group of shoals of even less than three fathoms 

 depth reaching to within five miles from the lightship location [Figure 7]. 

 With a topography of this character, particularly in a prominent region such 

 as that of Cape Hatteras, a very high degree of turbulence affecting the 

 distribution and mixing of the water both in its horizontal and vertical aspect 

 is plainly to be expected ... we furthermore see that the approximate inner 

 limit of the Gulf Stream, as determined by the United States Coast and 

 Geodetic Survey, cuts across the outer edge of the shoals less than three 

 fathoms deep off Cape Hatteras, and it therefore seems fairly certain that at 

 least the marginal warm waters of the Gulf Stream will commonly, to a 

 greater or less extent, be drawn into the turbulent mixing over these shoals. 

 While it is probable that the average inshore surface temperatures at Cape 

 Hatteras in mid winter may be somewhat lower than the average surface 

 temperatures at Diamond Shoals Lightship, it is therefore, on the other hand, 

 very improbable that the difference at this point should be nearly as great as 

 in the waters to the southwestward, and it is clear that the inshore belt of 

 lower temperatures, such as they may be, must under any circumstance be 

 greatly restricted in its width in the region of the shoals off Cape Hatteras," 



Figure 8 is a graphic representation of the surface temperature isotherms 



9. Functioning under contract with the Division of Oceanography, Hydrographic Office, 

 U. S. Navy. 



