(1) west-southwest toward the lower 

 Keys and distal island groups (Koczy 

 et al. I960, Rehrer et al. 1967); 

 and (2) south-southwest supplement- 

 ing the ebb flow and carrying sedi- 

 ments through the passes over the 

 middle Keys reef tract and into the 

 Straits of Florida (Turney and Per- 

 kins 1972, Marszalek et al. 1977). 

 Farther removed from the turbid 

 Florida Bay waters, the lower Keys 

 and distal islands receive waters 

 from the nearshore Florida shelf. 

 These waters are of variable tem- 

 perature and salinity and tend to 

 supplement the south and southwest- 

 erly flow of the Gulf Loop Current's 

 eastern edge (Jones et al. 1973, 

 Marszalek et al. 1977). In addition 

 to the winter's prevailing winds 

 there are sustained strong winds 

 from the southwest and northwest 

 associated with passage of cold 

 fronts (Multer 1977). The most 



obvious effect of these winds is to 

 pile up Florida Bay waters on the 

 northwest side of the upper Keys. 

 This tends to assist the tidal 

 movement of bay and gulf waters 

 through the middle and upper Keys 

 and into the straits of Florida 

 (Ginsburg 1956, Chesher 1974, 

 Marszalek et al. 1977). 



The previous description of 

 wind-driven currents in the Florida 

 Keys summarizes the dominant or 

 prevailing conditions. However, 



temporal variations of wind patterns 

 often cause currents to behave in 

 stark contrast to the norm, as il- 

 lustrated in Figure 40. Here the 

 effect of west winds on the water 

 level changes in Florida Bay can be 

 observed as a year round phenomenon 

 not restricted to winter months 

 (Ginsburg 1964). Although hurri- 

 canes are relatively rare, the 

 intensity and duration produce the 

 most severe wind currents observed 

 in the Keys (Ball et al. 1967, Per- 

 kins and Enos 1968). The currents 



that result from the passage of a 

 hurricane depend on the trajectory 

 and point of landfall. Ball et al. 

 (1967) provide an excellent descrip- 

 tion of the "Great" Hurricane Don- 

 na's passage over the middle and 

 upper Keys as well as the ensuing 

 geomorphic changes resulting from 

 currents, tides, and the storm 

 surge. Because of the cyclonic 



(counter clockwise) movement of 

 winds about the hurricane's eye, the 

 storm's passage may entail hurri- 

 cane-force winds from totally oppo- 

 site directions within the course 

 of a few hours (Gentry 1974). In 

 Donna's case this resulted in the 

 "draining" and "flooding" of Florida 

 Bay within a 24 hour period (Ball 

 et al. 1967). 



WATER LEVEL CHANGES IN FLORIDA BAY AT TAVERNIER 



u s 



- STRONG WEST WINDS 



J *J^ 



1958 



Figure 40. Water level fluctua- 

 tions in Florida Bay 

 at Tavernier (adapted 

 from Ginsburg 1964). 



Oceanic Currents 



Two oceanic currents affect the 

 Florida Keys hydrology; these are: 

 (1) the Gulf Loop Current, north and 

 west of the islands; and (2) the 

 Florida Current, south and east of 

 the Florida Keys. The precursor of 

 both Florida currents, the Caribbean 

 Current, is initially formed by the 

 union of the Guana and Equatorial 

 Currents to the northeast of South 



92 



