Frvi.n-^ Pan Shoals Lightship 



Surface temperatures tended to lag below the mean for the 

 period of record (I9l4?-19%) during the first half of the year except 

 for mid-February, The latter two -thirds of November tended well be- 

 low the mean and the latter two- thirds of December tended well above. 



Minimum temperatures of less than 59 F were observed in 

 January, Maximum at the surface, reater than 8l°F was reached in 

 late August and early September, at the bottom, 81 F at the same time. 

 The thermocline did not become ^as well developed at this location as 

 it did north of Cape Hatteras, The maxim.um gradient, surface to bot- 

 tom (70 feet) was never more than 9°F. The thermocline commenced de- 

 velopment in late April, yet during the first-third of June the water 

 column was again virtually isothenual. Ihe strong theiroocline dijring 

 the latter part of July was apparently due to a transgression of colder 

 water from offshore. 



The surface and bottom salinities seldom differed by more 

 than l°/oo and remained very close to 36°/oo except during November 

 when the salinity of the whole water column dropped to about 3U°/oo, 

 This was coupled with a depression in the temperature of the- whole 

 water column, followed by a return to higher salinity and teiT^jerature 

 in December, It aopears that two unusual phenomena were involved here 

 at nearly the same time. First there was a transgression of less sa- 

 line water followed by colder than normal weather causing a depression 

 in water temperatures. The extremely warm air te^-nperatures enjoyed by 

 the south eastern seaboard were reflected in the rise in water tempera- 

 ture in December. 



It is difficult to believe that the depression in salinity 

 throughout the whole water column was due to the off-shore movement of 

 coastal water, as a relatively shallow volume of such water when mixed 

 with a deeper, larger volume in th^ proportions available would not pro- 

 duce such a marked salinity deprersion. In consideration of the wind 

 systems prevalent at the time, we suspect this to be a parcel of coastal 

 water from north of Cape Hatteras carried southwesterly by a long period 

 of predominantly northerly and northeasterly winds. IVie speed of move- 

 ment of this parcel from Hatteras to the Lightship may have been on the 

 order of .7 - 8 miles per day. Tliis phenomenon has previously been postu- 

 lated by Bumpus and Pierce (1955, pp. 95 and 96). 



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