-Comparison of the direction and speed of ballasted (B) 

 and unballasted (U) bottles recovered within 15 days 

 after release in the Gulf of Mexico. 



Type 



Number 



Direction (True) 



Bottle Recovered Range 



Average 



Speed (km/day) 

 Range Averag 



230°-276° 

 007°-016° 

 347°-007° 

 244°-359° 



204°-215° 

 204°-205° 



331°-339° 

 292°-307° 

 292°-317° 



180*-195° 

 195°-009° 



336°-354° 

 341°-012° 



276° 

 268° 

 013° 

 357° 

 263° 

 244° 

 207° 

 204° 

 339° 

 334° 

 302° 

 305° 

 298° 

 298° 

 187° 

 334° 

 291° 

 291° 

 346° 

 360° 



1.9.-4.6 

 3.7-18.5 

 3.7-15.7 

 0.9-3.9 



17.0-21.1 



18.3-19.1 



5.9-6.3 



2.6-6.3 



2.4-4.8 



2.9-9.3 



6.3-8.3 



5.6-6.5 



5.6-26.8 



25.9-38.9 



5.9-38.9 



4.4-7.9 



8.3-14.6 



4.6 



4.1 



9.3 



11.7 



1.7 



1.1 



19.8 



18.7 



6.1 



3.7 



4.3 



5.0 



6.3 



7.0 



6.1 



10.7 



32.4 



20.0 



6.7 



9.8 



Resultant wind vectors for the cruise periods revealed 

 differences between areas in the northwestern Gulf as 

 well as differences between months. In January 1963, 

 winds at New Orleans were generally northerly or off- 

 shore, those at Galveston northeasterly or alongshore, 

 and those at Brownsville southeasterly or onshore. This 

 circulation pattern of winds may account for the absence 

 of recoveries of bottles released east of Galveston. 



In February 1962 and 1963 winds were generally 

 similar over the entire study area, i.e., east to southeast 

 flowing west alongshore at New Orleans and Galveston 

 and onshore at Brownsville. Strongest winds occurred at 

 Brownsville in both years and probably accounted for the 

 reduced rate of alongshore flow of surface waters 

 observed in that area. 



March-May. — Drift bottle movements indicated a 

 transitional period for surface currents in the study area 

 during both years with several distinct features (Figs. 3, 

 4). First, the flow of surface waters off Louisiana was 

 predominately to the west in March of both years, but as 

 time progressed, the flow direction generally shifted to 

 the north and became onshore in May. This onshore 

 component was more pronounced in May 1962 than in 

 May 1963 when some east to west movement was still ap- 

 parent. Apparent monthly differences in the timing of 

 the breakdown of the dominant east to west movement 

 between years may be accounted for by the difference in 

 cruise dates between years or may reflect real yearly dif- 



ferences. Associated with this dominant flow off Loui- 

 siana was a generally weak northward onshore movement 

 of nearshore waters just west of the Mississippi River. 



The second prominent feature during this period was 

 the movement of waters off the south Texas coast. 

 Recoveries during both years indicated an area of con- 

 vergence of currents. Furthermore, as the season pro- 

 gressed, this arc of convergence moved northward up the 

 Texas coast until the flow of surface waters became 

 almost directly onshore. In May 1963, however, this pat- 

 tern can only be inferred due to the paucity of drift bottle 

 releases off the south Texas coast. 



The third distinct feature of the circulation pattern 

 was the indication of the presence of an oceanic surface 

 current that existed in waters beyond the continental 

 shelf. This was particularly apparent in March of both 

 years and April 1962 when several bottles deposited on 

 the edge of the shelf apparently moved against (straight 

 line trajectory) prevailing shelf currents. From this set of 

 data, it appeared that in the surface waters three current 

 systems may have been present in the study area: a near- 

 shore countercurrent, a shelf current, and an oceanic cur- 

 rent. 



Current velocities varied depending on location with- 

 in the study area. Speeds of the dominant east to west 

 drift off Louisiana ranged between 7 and 14 km/day 

 whereas the weak onshore current just west of the Missis- 

 sippi River ranged from 1 to 3 km/day. Within the area of 

 convergence off Texas, speeds ranged from 3 to 17 km/ 



