Although the current does not usual- 

 ly enter the shelf, a strong north- 

 erly current is noticeable immedi- 

 ately seaward of the shelf break 

 from Key Largo northward (Enos 

 1977). Surface velocities in the 

 Florida Straits average about 150 

 cm/sec (5 ft/sec) (Brooks and Niiler 

 1975, Enos 1977, Jaap 1982). Thorp 

 (1935) and Vaughan (1935) postulate 

 that a countercurrent exists shore- 

 ward of the Florida Current over the 

 shallow shelf. Although reference 

 elsewhere in the literature has also 

 been made to this countercurrent 

 (Davis 1940, 1942, Ginsburg 1956, 

 NOAA 1973), Enos (1977) points to a 

 lack of adequate documentation to 

 justify this suppositon. He does 

 concede however, that a slight west- 

 ward component exists in addition to 

 the dominant tidal and wind-driven 

 currents. As discussed previously 

 (wind-driven currents), Enos (1977) 

 has observed strong northeasterly 

 currents near Molasses Reef for 

 several days seemingly independent 

 of tidal action and approximately 

 45° from the downwind direction of 

 the Seabreeze. He concludes that 

 the current was either the result of 

 "channelized" wind-driven currents 

 or a spin-off eddy of the Florida 

 Current blown over the Florida 

 Shelf. Lee (1975) observe these 

 spin-off eddies in the waters adja- 

 cent to Miami. These eddies vary 

 seasonally and monthly in their 

 speed and direction (e.g., the July 

 mean speed was 20 cm/sec or 39 

 ft/min; March and April means were 

 7 cm/sec or 14 ft/min). Enos (1977) 

 suggests that long term southwestern 

 "countercurrents" may also be an 

 artifact of altered nearshore tide 

 phase changes formed from the north- 

 east to southwest or from Miami to 

 Key West (discussed in greater 

 detail in the section on tides). 

 Finally Brooks and Niiler (1975), in 

 studying the Florida Current off Key 

 West during the early summer of 



1972, observe a counterflow travel- 

 ing at less than 25 cm/sec along the 

 northern edge of the Florida Straits 

 whereas the Florida Current was 

 observed to be traveling in the 

 opposite direction (to the ENE) at 

 less than or equal to 145 cm/sec 

 (49 ft/min). Although described as 

 a countercurrent extending from the 

 shore out 7 km (4 mi), the nearshore 

 data are based on only one station 

 located 25 km (16 mi) seaward of Key 

 West. 



Freshwater 



Freshwater reaches the Florida 

 Keys in one of two major ways: (1) 

 indirectly through fluctuating 



freshwater discharges from drainage 

 basins bordering the eastern Gulf of 

 Mexico; and (2) directly through 

 rainfall. Seasonal inflow from the 

 drainage basins reduce the salinity 

 of the Gulf Loop Current and Florida 

 Bay, in turn affecting the waters of 

 the middle and lower Keys (Wennekins 

 1959, Marszalek et al. 1977). Mars- 

 zalek et al. (1977) relate the more 

 restricted coral growth on the 

 distal islands (Dry Tortugas and 

 Marquesas Keys) and lower Keys to 

 the greater variability of salinity 

 and temperature of the Gulf Loop 

 Current. In contrast, these authors 

 point to the more luxurient coral 

 growth in the upper Keys reef tract 

 as a result of the more stable Flor- 

 ida Current salinity and temperature 

 regime which affects that area's 

 reef water. 



Rainfall in the Florida keys, 

 as previously discussed in the Cli- 

 mate section, is the lowest reported 

 for Florida averaging from 89 to 114 

 cm (35 to 45 in) annually and with 

 80% to 90% falling from May to Octo- 

 ber (Hanson 1980). Most of this 

 rainfall, because of the slight 

 geographic relief and the pervious 

 nature of the Key Largo and Miami 

 oolite rock formations, infiltrates 



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