Figure 41. Pathlines of the 22° 



isotherm at 100 meters 

 depth in the Gulf of 

 Mexico from August 



1972 to September 



1973 (adapted from 

 Maui 1977). 



previously proposed (Leipper 1970). 

 Maul (1977) instead suggests a pos- 

 sible relationship between the cycle 

 of Gulf Loop Current penetration 

 into the gulf, and cycles of: (1) 

 surface drift velocity of the Flori- 

 da Current; and (2) direct transport 

 of the Florida Current. He also 

 notes an inverse relationship be- 

 tween the penetration of the current 

 into the Gulf of Mexico and the 

 distance the current was found (22°C 

 or 72°F isotherm at 100 m or 328 ft) 

 from the Cosgrove Lighthouse located 

 between the Dry Tortugas and Key 

 West. 



The Gulf Loop Current's effect 

 on the nearshore waters of the Flor- 

 ida Keys is masked in many cases by 

 tide and wind driven currents. Chew 

 (1961) describes several cyclonic 

 currents along the western coast of 

 Florida powered by the kinetic ener- 

 gy from the adjacent Loop Current. 



These counterclockwise moving cur- 

 rents exist primarily north of Cape 

 Romano but at times entrain Florida 

 Bay waters, carrying it to the 

 north: alternatively they may also 

 "leak" waters along the western edge 

 of Florida Bay and through the Keys 

 to the Florida Straits. Florida 



Bay, for the most part, remains in a 

 current shadow with the surface 

 ocean currents of the Gulf of Mexico 

 apparently having little effect on 

 even the westernmost part of Florida 

 Bay (Turney and Perkins 1972). The 

 waters north of the lower Keys and 

 west of Florida Bay at times are 

 moved in a west-southwesterly direc- 

 tion pulled possibly by a venturi 

 action of the Gulf Loop Current's 

 south and southeasterly flow through 

 the distal island groups (Koczy 

 et al. 1960, Rehrer et al. 1967, 

 Murphy et al. 1975, Maul 1977). 



An interesting study following 

 the "red tide" as a natural tracer 

 of current patterns off south Flor- 

 ida is reported by Murphy et al. 

 (1975). The occurrence of Gymnodi- 

 nium breve and its associated fish 

 kills were traced from Sanibel Is- 

 land on the west coast to West Palm 

 Beach on the Florida east coast. 

 The red tide's movement from off 

 Sanibel Island to the Tortugas fish- 

 ing grounds suggested the involve- 

 ment of the Gulf Loop Current which 

 had been identified flowing south- 

 southwest over the southwest Florida 

 shelf (Maul 1977). 



The axis of the Florida Current 

 is still another factor in local 

 hydrology. Within the Straits of 

 Florida, the current's axis closes 

 in on the Florida coastline as it 

 progresses to the northeast. Off 

 the Dry Tortugas the current lies 

 124 km (77 mi) to the south. As it 

 approaches the waters adjacent to 

 the upper Keys, the current is 

 within 30 km (19 mi) of the islands. 



94 



