Chapter Five 



THE HYDROGRAPHY OF 

 THE GULF STREAM 



The first detailed series of hydrographic stations across the Gulf Stream 

 was that begun in 1931 by the Atlantis, then the only seagoing research 

 vessel of the newly founded Woods Hole Oceanographic Institution, and 

 consisting of soundings repeated quarterly for a number of years. 



'ATLANTIS' SECTIONS OF THE GULF STREAM, 1931-1939 



Many early sections were made between Bermuda and Chesapeake Bay 

 (Iselin, 1936) and between Bermuda and Montau' Point, New York 

 (Iselin, 1940). Temperature sections were made at four different seasons, 

 as sho\\Ti in figs. 19-22 ; and sahnity sections at the same seasons, as shown 

 in figs. 23-26. In these figures the vertical scale above the depth of 

 2000 m. is much exaggerated (a distortion of 1 : 370) ; but below 2000 m. it 

 is less so (1 : 148). The warmer the water, the less dense. The most striking 

 feature of all these sections is the pronounced change in level of the 

 isotherms in a narrow region. According to the geostrophic relation 

 [Chapter III, equations (4) and (5)], this narrow zone is where the high 

 current velocities, perpendicular to the plane of the page (in figs. 19-26), 

 occur. The surface of the waters to the left of the Stream, called slope water, 

 is subject to wdder seasonal fluctuations than the Sargasso water to the 

 right of the Stream, where the primary seasonal change is the appearance 

 of a shallow thermocline in the summer. 



