VELOCITY AND TRANSPORT OF THE ANTILLES CURRENT 

 NORTHEAST OF THE BAHAMA ISLANDS 



Merton C. Ingham' 



ABSTRACT 



Meridional geostrophic velocities and volume transports were computed from data collected on six 

 occupations of Standard Section A-7 by U.S. Coast Guard cutters. The section extends offshore from 

 Cape Canaveral, Fla., along lat. 28°35'N for about 520 nautical miles (960 km), but this study involved 

 only that portion seaward of the 800-m isobath (situated at about long. 79° 30'W), a portion which would 

 transect the Antilles Current just before it merges with the Gulf Stream. The velocity sections did not 

 reveal a broad northward flowing Antilles Current in the surface layer as has been shown on many 

 average current charts in the past. Instead, the sections revealed a generally sluggish (<10 cm/s) 

 surface flow, either northward or southward. Imbedded in the low speed surface flow were two bands of 

 higher speed (10-40 cm/s), one northward and the other southward, usually located in the vicinity of the 

 1,000-fathom (1,830-m) isobath. Computed net transport for the sections ranged from 30.4x10* mVs 

 northward to 6.4x10* mVs southward, with an average of 8.6x10* mVs northward, which is con- 

 siderably less than customarily h\-pothesized in the past to provide for the observed downstream 

 increase in Gulf Stream transport between the Straits of Florida and Cape Hatteras, N.C. 



The position of the band of relatively rapid southward flow corresponded approximately with the 

 position suggested by Kort for the southward flowing Antilles-Guiana Countercurrent. A comparison 

 of temperature-salinity properties in the bands showed them to be identical with each other but 

 different from Florida Current water, making it highly unlikely that the bands are manifestations of 

 two continuous currents, the Antilles Current and Antilles-Guiana Countercurrent, from different 

 source areas. The identical temperature-salinity properties of the bands indicate that they are 

 manifestations .of eddies or a countercurrent formed by recurving of an adjacent current; the former 

 alternative appears more likely. 



The importance of the Antilles Current as a means of transporting significant quantities of pelagic 

 ichthyopknkton into the Gulf Stream s.\-Btem is doubtful. The current speeds and transports appear to 

 be substantially less than hypothesized and highly variable. An alternate means of transport of 

 ichthyoplankton in the surface layer which may be in operation is Ekman drift generated by local 

 winds, yielding a flow which may not be reflected in the field of mass and geostrophic computations. 



One of the objectives of the initial ichthyoplankton 

 cruises of the MARMAP (Marine Resources 

 Monitoring Assessment and Prediction) program 

 of the National Marine Fisheries Service was to 

 estimate the transport of eggs and larvae of 

 pelagic fishes into the Gulf Stream system by the 

 Antilles Current. Scientists in the program began 

 gathering information and data from various 

 sources in an attempt to characterize the Antilles 

 Current and other currents in the area of interest, 

 the western North Atlantic and northern Carib- 

 bean Sea. These attempts revealed that the por- 

 tion of the Antilles Current east of the Bahama 

 Islands and northward has been little investigated 

 and is only sketchily described, even though 

 frequently mentioned in general works and shown 

 on charts of "average" or "permanent" surface 

 currents. Descriptions based on ship-drift data 



'Atlantic Environmental Group, National Marine Fisheries 

 Ser\'ice, NOAA, Narragansett, RI 02882. 



(U.S. Naval Oceanographic Office 1965; Boisvert 

 1967) portray the surface current in this region as 

 having a prevailing direction of flow toward the 

 north-northwest with a modal speed of about 0.5 

 knot (25 cm/s), an average speed of about 0.7 knot 

 (35 cm/s), and a directional persistence of 40-55% 

 in most of the area, except immediately north of 

 the Bahama Islands, where a pair of eddies are 

 shown (Figure 1). The strongest currents were 

 found in a narrow band 10-30 nautical miles (18-55 

 km) wide near the Bahama Banks. 



The junction of the Antilles Current with the 

 Gulf Stream generally has been thought to occur 

 over about 8° of latitude south of Cape Hatteras, 

 N.C, (about lat. 28°-36°N) with the current sup- 

 posedly adding about 60 x 10*^ m^/s to the transport 

 of the Gulf Stream, approximately tripling its flow 

 (Stommel 1965). Knauss (1969) concluded from 

 direct and indirect measurements of Gulf Stream 

 transport in the Florida Straits-Cape Hatteras 

 area that there is a gradual, uniform addition of 



Manu>cnpt accepted October 1974. 

 FISHERY BULLETIN: VOL. 73, NO. 3, 1975. 



626 j'i-i^'a^.V 



