GULF OF MEXICO 



123 



accurate of the methods now in use. Used in 

 conjunction witli the geomagnetic electrokineto- 

 graph, it probably provides the best complete 

 picture of the current patterns in the open Gulf. 

 Determination of the flow over the broad, shallow 

 continental shelf remains a diflicult problem. 



vSome processes by which the distribution of 

 density is caused to change are evaporation, 

 conduction, and the movement of masses of 

 water by the winds. Since the total transport of 

 water due to the winds in this hemisphere is 

 toward the right of the wind, and since this trans- 

 port consists of waters in the surface layers which 

 are warm and of low density, the low density 

 waters are piled up at the right of the wind flow, 

 which is in the center of anticyclones, regions of 

 good clear weather. The warm waters are 

 removed from the low pressure storm areas at the 

 left by the wind action. These movements are 

 called the wind-driven currents. Their primary 

 effect is to pile up water of small density in areas 

 of anticj'clonic winds and to leave waters of 

 greater density in areas of cyclonic winds. This 

 leads to a secondary effect, namely, the mainte- 

 nance of a different ocean current related to this 

 distribution of density. Since such currents flow 

 nearly perpendicular to a line connecting the 

 regions having the different water densities, the 

 associated currents form a pattern quite similar 

 to the pattern of the winds. This may readily 

 be recognized on charts showing the distribution 

 of ocean currents with prevailing winds super- 

 imposed. 



Investigations of ocean currents in the Gulf 

 of Mexico 



There is probably no part of the oceans of the 

 world of comparable size to the Gulf of Mexico 

 where there is such a wide difference of opinion 

 concerning the specific current regime. This 

 difference is brought out by Sweitzer (1898). He 

 quotes Isaac Vassius who, writing about the year 

 1663, tells how the currents through the Yucatan 

 Channel "turn obliquely" and pass through the 

 Straits of Florida. The issue of the Encyclopedia 

 Britannica available in 1898 states that "a portion 

 of it (the current — DFL) passes directly to the 

 northeast along the shore of Cuba; but by far 

 the larger part sweeps around the Gulf." Sweitzer 

 himself concludes that, at times "the channel of 

 Yucatan pours its waters into the Gulf so that 



they spread out in all directions moving on its 

 center," while at other times the currents flow 

 "in a northeasterly direction around the extreme 

 west coast of Cuba." These last results were 

 based upon studies of the distribution of specific 

 gravity of the surface waters. United States 

 Coast and Geodetic Survey, Lindenkohl (1896), 

 and upon modification of currents by the prevailing 

 winds. 



Sweitzer also reported considerable agitation of 

 the waters covering an area of about 100 square 

 miles occurring off the coast of Texas about 40 

 miles south and 20 miles east of Aransas Pass 

 which could only be accounted for by the meeting 

 of two opposing currents. Other evidence of 

 converging currents has since been found, and this 

 area has become known as the graveyard of ships. 



Measurements made in the years 1885 to 1889 

 by the United States Coast and Geodetic Survey 

 vessel Blake, commanded by Pillsbury (1889), 

 determined the currents in the Straits of Florida. 

 Since the ship was anchored, direct current ob- 

 servations could be compared to computed values, 

 and the comparison provided one of the best 

 examples illustrating the validity of the method 

 for computing relative currents which is now so 

 widely used. 



Agassiz (1888) published temperature and 

 salinity data collected by the Blake in 1878. 

 These data, together with others collected by the 

 Bache, Bigelow (1917), were used by Wvist to 

 compute the transport of the water through the 

 Florida Straits as 26 million m^second. As- 

 sociated with this transport is a water level 

 difference of 19 cm. between the southeastern 

 Gulf and the Atlantic at St. Augustine, Florida, 

 which is discussed by Montgomery (1938). A 

 theory of piling up water in the "Bay of Mexico" 

 was advocated by Benjamin Franklin about 1770. 



In 1922, the Dana made some observations in 

 the Yucatan Channel and in the Florida Straits, 

 as shown in figure 36. These observations, as well 

 as those of the Mabel Taylor in 1932, were sum- 

 marized by Parr (1935) who concluded that 

 "evidence thus obtained from the Gulf itself, 

 although directly opposed to some of his premises, 

 nevertheless serves to confirm the theory already 

 advanced by Nielsen on the basis of observations 

 in the Straits alone, that the so-called Gulf 

 Stream only takes the shortest possible path from 

 its entrance through the Yucatan Channel to its 



