migratory commercial and sport fishes due to sea- 

 sonal temperature changes. 



Several thermal transistional zones are appar- 

 ent (fig. 17). The first zone was between Cape 

 Cod and Cape Hatteras. A second zone was be- 

 tween Cape Hatteras and Jacksonville. A third 

 zone, not as well defined, was between 

 Jacksonille and Miami, Florida. 



A graph, (fig. 18), was constructed by plotting 

 the positive and negative monthly temperature 

 change at four selected sampling sections (20, 

 13, 9, 1) from figure 17. This figure shows the 

 seasonal temperature rate of change trends for 

 areas north and south of Cape Hatteras. The 

 trends are predicatable, since these areas have 

 separate water masses. An area which contained 

 two or more water mass boundaries (Cape Cod, 

 Cape Hatteras) has the greatest rate of tempera- 

 ture change (fig. 18). 



This condition would indicate that marine ani- 

 mals in coastal regions bound by two or more 

 water mass systems and of large ATs migrate 

 farther than those in coastal regions bound by only 

 one or two water mass systems but of a small 

 AT. Hence, this would impact more on the fishing 

 industry in the coastal areas north of Cape Hat- 

 teras than areas south of Cape Hatteras during 

 July 1969 through June 1970. i.e.. fish should 

 migrate farther and the climate should be more 

 variable. 



Thermal Front (Cape Hatteras to Miami) 



Aerial temperture observations have been used 

 to track the Gulf Stream's thermal front since 

 1953 (von Arx et al., 1955). The Gulf Stream's 

 thermal front when tracked by ART, can be 

 masked by the overlapping or "shingling" of warm 

 Gulf Stream water over the cooler Slope Water 

 (Bratnick, 1970). Bratnick's study was conducted 

 north of the area covered in this report; however, 

 evidence of some surface shingling did occur on 

 ART surveys east and north of Charleston, South 

 Carolina but became less noticeable as the Gulf 

 Stream approached Cape Hatteras. Oilier areas 



affected by "shingling" were the latitudes south of 

 Palm Beach to Miami, Florida during summer 

 months when solar radiation heated the surface 

 film and masked the already small thermal gra- 

 dient separating the Gulf Stream and warm coas- 

 tal waters to the west. Wind mixing of the two 

 water masses sometimes better defines the exist- 

 ing surface gradient; however, wind in excess of 

 25 knots generates sea spray, which becomes 

 aerated, thus attenuating the ART measurements 

 and masking the thermal front. 



Without the aid of bathythermographs we can 

 only assume that the strong thermal gradient indi- 

 cated by the ART trace was the actual location of 

 the Gulf Stream's thermal front. The actual point 

 on the ART signature chosen as the thermal front 

 crossing is defined as the first temperature value 

 on the warm side of the signature slope and is 

 indicated by the point [A], (fig. 19). Sometimes a 

 visual indication accompanied the temperature 

 change. These visual indications included lines 

 of sargassum sea weed, water color changes, in- 

 creased sea state on the warm side of a thermal 

 front, and occasionally the formation of cumulus 

 clouds on the warm side of the thermal crossing. 

 The variations of the thermal front associated with 

 the Gulf Stream divided into 3 month intervals 

 from July 1969 to June 1970 between Miami, 

 Florida and Cape Hatteras, North Carolina, (fig. 

 20), led to these conclusions. 



• No appaient seasonal pattern existed be- 

 tween the thermal front positions and dis- 

 tance offshore. 



• Yearly lateral (east to west) oscillations 

 along the thermal front were limited in mag- 

 nitude between Miami and Cape Canaveral, 

 Florida (8 to 18 nmi. ); increased from Cape 

 Canaveral, Florida to a maximum variation 

 off Cape Ltjokout. North Carolina (18 to 40 

 nmi.); decreased between Cape Lookout 

 and Cape Hatteras (40 to 12 nmi.); and in- 

 creased again north of (^apc Hatteras. 



• In general, the thermal front paralleled the 

 183 meter isobath. 



