68 Hydrography of the Stream 



THE FLORIDA CURRENT 



Most of the water in the Florida Current comes through the Yucatan 

 Channel from the Caribbean Sea, rather than from the Gulf of Mexico 

 (Iselin, 1936). The water is forced through the long channel between the 

 Florida peninsula on one side and the islands of Cuba and the Bahamas 

 on the other by a head of water of about 19 cm., as inferred from a leveling 

 survey across Florida. The Straits between Key West and Havana are 

 140 km. wdde, and their greatest depth is 1500 m. This channel becomes 

 narrower and shallower dowTistream, takes an abrupt 90° turn to the left, 

 and reaches a minimum cross section off Miami, where the width is 80 km. 

 and the greatest depth is 800 m. The stream then flows north along the 

 continental shelf to about 33° N. latitude, where it leaves the shelf and 

 flows into deep water south of Cape Hatteras. From Cape Canaveral 

 north, the Florida Current increases in mass transport. This is particularly 

 obvious at the place where it leaves the continental shelf and begins to 

 carry water at temperatures lower than 8° C. along mth it. There is also 

 supposed to be an increase of volume transport by confluence Mith the 

 Antilles Current immediately north of the Bahamas (IseHn, 1936), but 

 evidence concerning the transport of the Antilles Current is conflicting. 



The mass transport of the Florida Current is estimated to be about 

 26 X 10®m.^/sec. The computed values vary considerably, as is shown by 

 computations (Montgomery, 19416) made from four Atlantis sections 

 across the Straits at Havana: March 4, 1934; February 19-20, 1935; 

 April 12-13, 1935; and March 24-25, 1938. The transports computed are 

 26-0, 30-3, 29-0, and 260 x 10® m.^/sec, respectively. There are numerous 

 sources of error in such computations : first, the level of vanishing hori- 

 zontal pressure gradient must be assumed; secondly, the geostrophic 

 equiHbrium may not hold strictly ; thirdly, there are gaps between the end 

 stations and the shore where transport must be estimated; and, fourthly, 

 tidal effects on the density field may upset the computation. Woodcock 

 (see Parr, 19376) made a series of anchor stations across the Straits at 

 Miami which show marked semidiurnal variation in the density structure. 

 Parr (19376) has described a highly speculative process of cross-stream flow 

 based on Rossby's (19366) wake-stream analogy. It seems to me that the 

 tidal influence on the density structure in the Straits of Florida might be 

 of the nature of an internal seiche. The dimensions of the channel at 

 Miami and the density* structure appear to favor a resonance in a cross- 

 stream semidiurnal internal seiche. 



Since the tides in the Gulf of Mexico are very small, one would suppose 

 that there is a tendency for a semidiurnal progressive tidal wave to move 

 upstream from Miami. A study of the tidal constants at various points 



