SALINITY OF OCEAN-WATER AT FOWEY ROCKS, FLORIDA. 313 



If this explanation is correct the normal content of chloride of sea-water 

 off Fowey Rocks is more nearly represented by the average of the deter- 

 minations that do not fall abnormally below a certain minimum. To obtain 

 this normal content the two very high estimates and the 57 estimates that 

 fall below 19.72 have been omitted; the average of the remaining 329 esti- 

 mates is 19.93 grams per kilogram of chloride. This corresponds to a salinity 



y.Ov 



of 36.00 grams per kilogram and a specific gravity (-5) of 1.02894. The 



average content of chloride of sea-water in the Gulf of Mexico, according to 

 the average of 52 determinations on consecutive daily samples collected in 

 June 191 3, from Southwest Channel, Tortugas, is 19.93. x Consequently 

 it may be concluded that the normal salinity of the Gulf Stream off Fowey 

 Rocks is like that of the Gulf of Mexico, but that it is decreased at times 

 by rains and by discharge of fresh water from Miami River and underground 

 aquifers along the coast. 



COMPARISON WITH SALINITY AT OTHER PLACES. 



The accompanying table giving the chloride content and salinity of 

 sea-water at other places on or near the coast of Florida, furnishes data 

 for comparison with the concentration at Fowey Rocks. The range in 

 concentration of samples collected June 23, 1913, from various places in 

 and outside Biscayne Bay shows the effect of fresh water from Miami 

 River and other less abundant sources. The salinities of the samples taken 

 outside the reefs on that date agree closely with each other and with the 

 salinity of gulf water at Tortugas (36.01). The water in the south part 

 of the bay is somewhat more concentrated, three samples having salinities 

 of 36.73, 36.64, and 36.64, respectively. This evidence that the water in 

 this part of the bay is concentrated by evaporation during its retention in 

 the shallows serves further to indicate that circulation there is not very 

 rapid and that the greater bulk of the water inside the keys is not thoroughly 

 mixed or shifted by the tides. The inside samples only as far south as Old 

 Man Beacon give evidence of dilution by fresh water; therefore it may be 

 concluded that, at the time these samples were collected, the effect of Miami 

 River on the water of the bay did not extend south of Soldier Key nor out- 

 side the keys. Yet the longer series later examined at Fowey Rocks shows 

 that the diluting effect is at times apparent as far out as the lighthouse. 

 The sample taken off the mouth of Miami River, June 23, 1913, has a salinity 

 obviously higher than the pure water of the river alone may be expected to 

 have and represents admixture with bay-water. Similar diluting effect is 

 shown by the two samples collected September 6, 1914, at different distances 

 from the mouth of Miami River, after a rainfall of i\ inches in 2 hours. 



The average chloride content of 22 samples of sea-water collected on 

 a voyage from Cape of Good Hope to England and analyzed by C. J. S. 



■See table, p. 302. 



