STA 5B 3 



20-75°C. 



TEM PE RATURE 



Figure 17. — Temperature profile and temperature-depth curves for the first(B) triplet of hydrocasts at front 5(22 April 

 1961). c = cool side; m = middle; w = warm side; • = Nansen bottle depths in profile. 



change, we get a density range from 12 to 114 

 cl.ton-l/lO miles between 15° and 20° C. and 

 from 14 to 135 cl. ton" V 10 miles between 

 20° and 25° C, The front at Cape San Lucas 

 had a density difference across it at the sur- 

 face ranging from 88, on the BT pass, down 

 to 14 cl.ton"!/ 10 miles on the E series hydro- 

 casts (see text table on p. 25, and figs. 21, 

 22, and 25), well within the range suggested 

 by Uda's figures. The fronts studied by Crom- 

 well and Reid, and by Knauss, apparently had 

 greater density differences across them at 

 any given depth. 



In the B series (fig. 23) the density dif- 

 ferences across the front are much more 

 pronounced at som^ depths than at others, 

 but in any case are small below 50 m. In the 

 E series (fig. 24) the differences are much 

 smaller but are the smallest between 75 and 

 100 m. These facts suggest that mixing had 

 taken place during the lapse between the two 

 series of hydrocasts, but had not extended 

 noticeably below 75 m. 



Because the Cape San Lucas front clearly 

 persists throughout spring and summer, one 

 might suggest that the products of mixing of 

 its constituent water masses are removed 

 from the area. This might partially explain 

 the reduced sharpness of the frontal system 

 with increasing distance from Cape San Lucas 

 (fig. 2). With respect to density gradient, front 

 5 differs from fronts 2 and 4 which are dis- 

 cussed later (p. 46 and 48). if a density dis- 

 continuity is a prerequisite for the formation 

 and persistence of a true front, fronts 2 and 

 4 are more typical than front 5. 



T, S, 8t distribution at the surface on a B T 

 pass. --At each BT lowering, we measured the 

 sea- surface temperature by bucket thermom- 

 eter and took a surface water sample for 

 salinity determination; we then computed the 

 8 T values. The values of these three principal 

 properties ( T, S, Sx) ^^ each BT across the 

 front during the third BT pass are shown in 

 figure 25. We computed the gradients as 



24 



