SOME ASPECTS OF THE PHYSICAL OCEANOGRAPHY 

 OF THE GULP OF MEXICO 



(Based on data collected on the 

 cruises of the ALASKA) 



By 



Kenneth H. Drummond 

 and 

 George B. Austin, Jr. 



Temperature . A large number of sea 

 surface temperature observations have been 

 collected in the Gulf of Mexico. Probably 

 the sea surface temperature values most 

 referred to in this area are those of 

 Fuglister (1947). These are mean isotherms 

 and show variation from month to month. 

 The main feature of the average winter pat- 

 tern is a gradual decrease from approxi- 

 mately 75° F. (23.9* C.) in the south to 

 65* F. (18.3* C.) in the north for all parts 

 of the Gulf. The gradient is larger in the 

 eastern portion. In the summer the average 

 temperatures approach uniformity at 84* F. 

 (28.9* C.) throughout the region. However, 

 measurements made during the cruises of the 

 ALASKA indicate that considerable deviation 

 from these average isotherms may occur at 

 certain times. For exEimple, in August the 

 mean charts show a temperature of 84* F. 

 (28.9" C.) throughout the Gulf whereas 

 ALASKA data show variations from 85* F. 

 (29.4* C.) to 89* F. (31.7* C. ) for the 

 northejistern portion of the Gulf. 



Temperature-depth sections (surface to 

 1000 meters) for the first three cruises of 

 the ALASKA are presented pictorially in 

 figure 1. Station positions and cruise 

 lines for each of the cruises are incorpo- 

 rated into the illustration to assist in 

 orienting the temperature-depth sections. 

 A scale of depths in 100-meter intervals 

 and a key to the temperature ranges are 

 given in the legend. Temperature-depth sec- 

 tions for the sh2illow continental shelf 

 areas are omitted and the omission is indi- 

 cated by the dashed cruise lines (i.e. 

 western Gulf and northwestern Gulf). 



Histograms showing frequency of the 

 distribution of temperature 2md salinity 

 at various depths greater than 800 meters 

 for cruises 1-lA, 2-2B, and 3-lC are pre- 

 sented in figure 2. 



Salinity . Until a systematic oceano- 

 graphic survey of the Gulf was made by the 



ALASKA even fewer data than those of 

 temperature were available on surface salin- 

 ities. Parr (1935) prepared a chart of the 

 distribution of average salinities for the 

 upper 50 meters. This chart shows a range 

 of 36.00 °/oo to 36.25 °/oo for the Gulf 

 region. More recent data on sea surface 

 salinities obtained on the ALASKA cruises 

 are presented in figures 3 through 8. Data 

 from cruise 8-3C lacked continuity between 

 station lines in both space and time aind 

 were therefore omitted. 



Histograms showing the frequency of 

 the distribution of salinity and temperature 

 at Vcirious depths from 800 meters to 2,000 

 meters are presented in figure 2. 



Depth of Motionless Layers . A study 

 of the depth of the motionless layer in the 

 Gulf of Mexico was mjide by Adams (1954) 

 using the methods of Defant and Hidaka. 

 Data used in this study were obtained on 

 cruises 1-lA, 2-lB and 3-lC of the ALASKA. 

 Excerpts from Mr. Adams' report are as 

 follows : 



"A comparison of the results of the 

 methods is of interest. It will be 

 noted that with Defant 's method (see 

 figure 10), two maxima are obtained, one 

 in the western Gulf and one in the east 

 central Gulf. These maxima also appear 

 in Hidaka' s method but both are of dif- 

 ferent magnitudes. The western Gulf 

 maximum in figure 10 is found to the 

 southeast using Hidaka' s method with the 

 latter being about 300 m. greater than 

 the former. The east central maximum in 

 figure 10 is again displaced to the 

 southeast using Hidaka' s method, but in 

 this case the latter is about 600 m. 

 smellier than the former. Both methods 

 show a variation in depth of the motion- 

 less layer of from 200 to greater than 

 1,000 m. Moreover, the methods show 

 good agreement in the area of Yucatan 

 Channel and fair agreement in the Straits 

 of Florida." 



Currents . The cruises of the research 

 vessel ALASKA provided the first complete 

 coverage of the Gulf of Mexico with informa- 

 tion needed to compute the deep water cur- 

 rents. It was on the basis of these current 

 patterns that sufficient evidence was ac- 

 quired to point out the existence of a 

 large-scale, semi-permanent, anti-cyclonic 

 eddy in the eastern Gulf. 



