GULF OF MEXICO 



135 



way the seasonal difForences. These curves are 

 presented in fio;ure 43 which gives the date and 

 position of each observation. Typical curves 

 properly selected are believed more representative 

 of conditions than average ones, since certain 

 characteristic features of temperature structure 

 may be lost in the process of averaging. A report 

 by Adams and Sorgnit (1951) gives similar infor- 

 mation for each 1° quadrangle of the Gulf where 

 data were available. It also shows the contours 

 of the bottom of the mixed or isothermal layer in 

 summer and winter insofar as can be determined. 



SALINITY 



Parr (1935) presents a chart of the distribution 

 of average salinities in the upper 50 meters of the 

 Gulf of Mexico. It shows the values to be typ- 

 ically 36.00 parts per thousand over the entire 

 central region. Water from the Mississippi River 

 reaches to depths of 50 meters and extends beyond 

 Mabel Taylor station 1106 (fig. 36), a distance of 

 150 miles, keeping salinities below 36.00 parts per 

 thousand. Near stations 1201 and 1202 the river 

 extends its influence on salinity only about 85 

 miles seaward. 



From the Yucatdn Channel a subsurface in- 

 trusion of water having salinity over 36.50 parts 

 per thousand extends north and bends westward 

 to the central part of the Gulf. From February 

 to April this tongue underwent a marked shift 

 westward in position of some 120 miles according 

 to the Mabel Taylor data. 



Above 50 meters waters of salinity greater than 

 36.25 parts per thousand are found over both the 

 wide Campeche and Florida Banks indicating 

 possible upwelling of the subsurface intrusion. 



Average variation of salinity with depth is 

 shown in table 3. 



TEMPERATURE-SALINITY 

 RELATIONSHIPS 



An average temperature-salinity relationship for 

 the Gulf proper was shown in table 3. A single 

 station tj'pical of what Parr defined as the Gulf 

 Complex is Mabel Taylor station 705 (fig. 36). 

 Another which he calls typical of the Caribbean 

 Complex, divided from the Gulf Complex by a 

 line extending from the northeast corner of Yuca- 

 tan Bank to the southwest corner of the Florida 

 Bank, is station 701 (fig. 36). Data for these sta- 



tions are listed in table 4. The primary difference 

 l)etween these two distributions is that at temper- 

 atures above 18° C. the Gulf Complex station has 

 markedly lower salinities, being below 36.32 parts 

 per thousand, while the Caribbean station has 

 values as high as 36.73 parts per thousand. 



The T-S curves in the Yucatdn Channel do not 

 seem to vary significantly from year to year, but 

 those in the Straits of Florida are not so stable, 

 particularly at temperatures above 20° C. 

 Cruises in different years in the Straits have 

 shown wide variations in the extent of Gulf 

 water found in the upper 200 meters. 



Table 4. — Typical temperature and salinity data 

 [After Parr) 



Parr (1935) believes that since — 



The presence of Gulf waters in the Straits of Florida 

 is ... identified with the location in which a counter- 

 current running in the opposite direction of the Caribbean- 

 Florida Current flow is usually indicated on the hydro- 

 graphic charts. ... it seems reasonable to draw the 

 tentative conclusion "the water masses of the Gulf of 

 Me.xico proper should be considered part of the coastal 

 water system of the North and Central American Atlantic 

 seaboard and not as part of the oceanic- circulation system 

 of the Caribbean and Florida Currents." 



Considerable further evidence is required to 

 fully support this tentative conclusion. 



Below 800-1,200 meters depth observations of 

 the Mabel Taylor showed hydrographic conditions 

 in the Gulf so extremely uniform that it was not 

 considered advisable to attempt to prepare verti- 

 cal profiles for the deep layers. More accurate 

 depth determinations on subsequent investigations 

 may bring out significant variations at these 

 depths. 



