America. From this union the cur- 

 rent flows west-northwest parallel- 

 ing the north coast of South America 

 towards Central America. As it ap- 

 proaches the Central American coast 

 it turns northward passing into the 

 Yucatan Straits and is renamed, 

 appropriately, the Yucatan Current. 

 The Yucatan Current's life is rela- 

 tively shortlived; as it moves north 

 and northeast it develops into two 

 distinct branches. One flows to the 

 north into the Gulf of Mexico; the 

 other flows directly towards the 

 Florida Straits. The former branch 

 of the Yucatan Current, called the 

 Gulf Loop Current, flows in a clock- 

 wise direction in the gulf, return- 

 ing to join the other branch of the 

 Yucatan Current in the Florida 

 Straits. The merger of these two 

 branch currents give rise to the 

 Florida Current which flows in an 

 east-northeast direction along the 

 eastern side of the Florida Keys 

 outer shelf and then north along the 

 Atlantic coastline. Within the 



Florida Current the two branches of 

 the Yucatan Current retain their 

 distinctiveness, segregated by dif- 

 ferences in salinity and temperature 

 (Wennekins 1959). The Gulf Loop Cur- 

 rent forms the western core which 

 lies closest to the Florida Keys and 

 exhibits a greater temperature and 

 salinity variability than the east- 

 ern core (Wennekins 1959). 



The extent of the Gulf Loop 

 Current's penetration into the Gulf 

 of Mexico is extremely variable from 

 year to year and seasonally. Its 

 northward intrusion into the gulf 

 extends, at times, as far as the 

 Mississippi Delta, and, at other 

 times, is restricted to an area 

 south of 24°N latitude, parallel to 

 the Florida Keys (Leipper 1970). 

 Longitudinally the Loop Current and 

 its spinoff eddies may extend east- 

 ward over Florida's western shelf, 

 and westward as far as the Texas 

 coastline. This current usually 



transports more than 25 million 

 m^/sec of water at speeds from 50 

 to 200 cm/sec (2 to 7 ft/sec) large- 

 ly contained in a band 90 to 150 km 

 (56 to 93 mi) wide (NOAA 1973). 



Maul (1977) provides one of the 

 most complete descriptions of the 

 Gulf Loop Current available to date. 

 He examines previous theories de- 

 scribing the current's movements in 

 light of an additional 14 month 

 survey of the 22°C (72° F) isotherm 

 at 100 m (328 ft) depth conducted 

 during a period from August 1972 to 

 September 1973. Figure 41 illustra- 

 tes the 22°C (72°F) isotherm path- 

 lines at 100 m (328 ft) monitored 

 during this 1972-73 period. This 

 figure portrays the geographic rela- 

 tionship between the Florida Keys 

 and the Gulf Loop Current's pathway. 

 At times, as previously stated, the 

 current impinges into an area over 

 the Florida shelf. For example, 



during August 1972 the current was 

 located tangentially to the Florida 

 Platform near the Dry Tortugas. 

 From September 27-28, 1972, the cur- 

 rent flowed dirctly toward the west 

 Florida shelf and, according to Maul 

 (1977), "there was evidence of Loop 

 Current water on the shelf, and the 

 22°C (72°F) isotherm apparently went 

 aground well north of the Dry Tortu- 

 gas. By early November, the current 

 has reformed to its southernmost 

 extent, and evidence of Florida Bay 

 wter flowing south through the Keys 

 was noted in both the ship track and 

 a LANDSAT image". Maul (1977) 

 reviewed previous 22°C (72°C) iso- 

 therm pathlines presented by Leipper 

 (1970), Whitaker (1971), Robinson 

 (1973), and his own work to illus- 

 trate the temporal and spatial vari- 

 ability of the Gulf Loop Current's 

 flow from year to year. 



Based on this variability. 

 Maul (1977) questions the validity 

 of the annual cycle and fixed sea- 

 sonal aspects of the Loop Current as 



93 



