be about 130 meters thick. A third probe, BT R, was dropped well with- 
in the warm core of the Gulf Stream. 
Four days later, on 16 May (figure 6), the area was resurveyed. 
Major features present on 12 May, though somewhat deformed, were easi- 
ly identifiable. However, general northeastern displacement of the 
Gulf Stream is evident through comparison of the 22°C isotherm for each 
flight. Maximum temperatures recorded in the Gulf Stream and cold 
tongue by AXBT show no significant change within the period of obser- 
vation. BT's S, T, and U show thermal structure in the cold tongue, in 
the Gulf Stream, and in the warm area, respectively. 
DISCUSSION 
Warm-Water Areas 
Of the warm-water areas observed during the present survey, only 
two had characteristics similar to those reported previously by Ichiye 
(1966, 1967) and Fisher (1969). The first of these, a small intrusion 
of 17° water extending westward toward the shelf, was observed on 28 
and 29 January. The small size and weak gradient delineating the warm 
area suggest that the observed feature is near extinction. The second, 
a warm water intrusion observed on 30 April, is distinguished by shape 
(inverted "J'') and separation from the Gulf Stream to the south by a 
cold intrusion. Other warm areas observed during the flights appeared 
to be small waves of the northern edge rather than a closed eddy or 
tongue. Considerable short-term areal change occurred as shown by the 
twofold increase in size observed within a 4-day period in May. 
Thickness of the warm area, when observed by ship or aircraft, appeared 
to be on the order of 100 meters. 
The vertical extent of the warm water and its relationship to 
adjacent water masses are shown in a cross section along 37°20'N (line 
AA', figure 6) taken by the USNS GILLISS (T-AGOR-4) during a combined 
air-sea survey in May 1969 (figure 7). The cross section, taken by 
shipboard expendable bathythermograph (SXBT) probes, transects the 
northern edge of the warm water and enters Slope Water before termi- 
+ nating just beyond the northern edge. The slope gradient and under- 
lying temperature inversion are evident at the edge of the Continental 
Shelf. Surface temperatures on the shelf are comparable to those 
taken on other tracks during the same survey and are about 2°C greater 
than those in the cold intrusion. One explanation for the higher 
temperatures is inhibition of vertical mixing in shallow water by a 
strong thermocline, thus limiting heat gain from solar radiation to 
the surface layer. Depth of the warm water, as measured by the 20°C 
isotherm, is about 25 meters. Temperature of the inversion (7.5°C at 
50 meters) beneath the frontal zone separating the warm water from 
Slope Water to the east is similar to that in the inversion impinging 
upon the Continental Slope, thus suggesting a similar source. The 
northern edge is identified by (1) abrupt temperature change (14.9 to 
