Temperature variation is pri- 

 marily controlled by depth and cir- 

 culation. In the nearshore shallow 

 waters adjacent to the islands, a 

 diurnal pattern follows daily 

 changes in air temperature. Along 

 the shelf break a seasonal pattern 

 characteristic of the Florida Cur- 

 rent is prevalent. Shinn (1966) 

 reports that both mean monthly and 

 annual temperature ranges along a 

 transect from Key Largo Dry Rocks to 

 Key Largo increase moving shoreward. 

 Temperatures during the 1961-1962 

 monitoring program range from 20° to 

 30.5° (68° to 87°F) at the outer 

 shelf margin; 17.2° to 32.8°C (63° 

 to 91°F) at an inner shelf margin 

 patch reef; and 13.2° to 33.8°C (56° 

 to 93°F) at a Key Largo nearshore 

 area. Jones (1963) observes as much 

 as a 6°C (11°F) daily variation over 

 a patch reef in the upper Keys. In 

 shallower waters the diurnal re- 

 sponse increases, resulting in rapid 

 temperature changes as great as 8°C 

 (14°F), dropping as low as 10°C 

 (50°F) during the passage of synop- 

 tic cold air masses (Zischke 1973, 

 Multer 1977, Little and Milano 1980, 

 Zieman 1982). 



Salinity variation, like tem- 

 perature, is controlled by depth and 

 circulation which affect the volume 

 of water and the surface area. In 

 shallow areas, temperature is af- 

 fected as the volume is reduced 

 thereby providing a smaller mass to 

 heat. With an increase in the sur- 

 face area to volume ratio, heating 

 and cooling are facilitated. With 

 salinity, the reduced volume and 

 increased surface area to volume 

 ratios produce an analagous result. 

 The smaller the volume of water, the 

 greater the influence of rainfall on 

 decreasing the salinity, and the 

 greater the influence of evaporation 

 on the increasing salinity. A 



greater surface area promotes rapid 

 mixing of precipitation, while at 



the same time promoting evaporation; 

 temperature increases and increased 

 wind/surface contact tends to re- 

 place "wet" air with "dry" air. The 

 salinity increases gradually from 

 reef to shore, as illustrated in 

 Figure 43 and, like temperature, 

 salinity exhibits a pulse over the 

 inner reefs shoal fringe where cii — 

 culation is restricted and shallow 

 depths exist (Enos 1977). Chew 

 (1954) observed salinity in the fore 

 reef area ranging from 36%-37% and 

 in the back reef or inner shelf from 

 33%-37%. Additional salinity data 



from the Keys nearshore environment 

 falls within a range similar to 

 Chew's (1954) back reef data, aver- 

 aging from 33.8% to 40.4% (Springer 

 and McErlean 1962, Little and Milano 

 1980). 



Within the channels and passes 

 of the lower Keys, and the sounds, 

 lagoons, bights, coves, and salt 

 ponds on the islands themselves, 

 depth and circulation are further 

 reduced with concurrent increases in 

 salinity and temperature variation 

 (Bock 1967, Howard and Faulk 1968, 

 Howard et al. 1970). Annual temper- 

 ature and salinity ranges appear to 

 be inversely proportional to depth 

 within Pine Channel (lower Keys). 

 At a depth of 15 cm (6 in) the mean 

 monthly salinity range was 12 ppt 

 for a 12 month monitoring program. 

 At 90 cm (35 in) the mean monthly 

 range decreased to around 9.8 ppt. 

 At depths from 1.35 to 1.95 m (4.4 

 to 6.4 ft) the range of mean monthly 

 values decreased to 6.0 ppt. Vari- 

 ation at each site was related to 

 local rainfall, evaporation, and 

 in shallow depths, to tides (Bock 

 1967). 



Turbidity is controlled by 

 depth, sediment type, vegetative 

 cover, bottom geography, and circu- 

 lation. In general, turbidity along 

 transects from reef to nearshore 



102 



