ber 1967 through February 1968. By late 

 January, the cooling effect extended to a depth 

 of 200 m. The minimum surface temperature 

 (17.37°C) was recorded on 1 March 1968, after 

 which a gradual warming of the surface layer 

 was noted. After remaining relatively constant 

 during April and May 1968, the sea surface 

 temperature began to increase until the maxi- 

 mum temperature value (25.27°C) was reached 

 on 1 August 1968. Temperature values re- 

 mained near the maximum value through Sep- 

 tember before cooling caused a gradual decline 

 throughout the remainder of the observational 

 period. 



During November and December 1967, the 

 water column was isothermal to a depth of 

 about 85 m. As cooling continued, the depth 

 of the isothermal layer increased. By late Jan- 

 uary 1968, it had reached a maximum depth 

 of about 200 m. During March and April 1968, 

 the surface water layer began warming slowly. 

 Below the gradually deepening layer of warmer 

 surface water, the water column remained iso- 

 thermal to almost 200 m. By May 1968, surface 

 heating and wind mixing had combined to 

 destroy the subsurface isothermal layer. As the 

 surface water mass began to cool in September, 

 an isothermal layer developed and had reached 

 a depth of 100 m by early December 1968. 



Seasonal temperature variation was confined 

 to the upper 200 m. A main thermocline was 

 observed during the entire observational period 

 approximately between 200 and 800 m. Below 

 800 m the temperature values remained rela- 

 tively constant with depth and showed little 

 variation during the year. 



A strong correlation existed between the 

 temperature and salinity cycle observed be- 

 tween November 1967 and December 1968; 

 temperature increases and decreases were 

 usually matched by similar changes in salinity 

 values. Surface salinity values during the ob- 

 servation period ranged from 36.08%o to 

 36.55%o. The annual salinity cycle was char- 

 acterized by lower salinity values in the surface 

 layer during the cooler winter months, and 

 higher values during the summer. The top of 

 the permanent halocline at about 250 m effec- 

 tively marked the limit of seasonal salinity 

 variations. The halocline extended to a depth of 

 approximately 700 m. Beneath the halocline, 

 salinity values were relatively constant with 



depth and time down to 1,500 m. 



In November-December 1967, salinity values 

 increased with depth from the surface, reach- 

 ing a maximum value at approximately 110 m. 

 Between January and May 1968, the water 

 column was essentially isohaline in the top 

 200 m. During the summer months from early 

 June to the middle of August 1968, salinity 

 values were highest at the surface and de- 

 creased with depth. In the last half of August 

 1968, a salinity maximum again occurred be- 

 tween 75 and 100 m, and by November 1968, it 

 was found at depths between 120 and 170 m. 



In addition to the annual temperature and 

 salinity cycles, temperature and salinity cycles 

 having periods of 2 to 3 months were noted at 

 depths between 200 and 800 m. During each 

 cycle, temperature and salinity values increased 

 to a maximum during a 2- to 4-week period, 

 before decreasing to minimum values 2 to 5 

 weeks later. Maximum values occurred on 26 

 January, 18 March, 5 May, 11 August, and 19 

 October 1968. The temperature difference be- 

 tween maximum and minimum values ranged 

 from approximately 1.2 C° in May 1968 to 

 3.4 C in March 1968. The salinity difference 

 ranged from 0.35%o in May 1968 to 0.58%o in 

 March 1968. A possible explanation for the 

 cycles was the periodic intrusion of warmer, 

 more saline Gulf Stream water through ECHO 

 caused by meandering of the current. 



Two principal water masses were observed in 

 the top 1,500 m of the water column at Ocean 

 Station ECHO. North Atlantic Central Water, 

 characterized by a nearly straight T-S curve 

 between the points T = 8°C, S = 35.10%o and 

 T = 19"C, S=36.70%o (Sverdrup et al. 1942, p. 

 668), was present at depths from 200 m to 

 about 800 m. 



At intermediate depths (800-1,500 m) the 

 water mass present at ocean station ECHO is a 

 mixture of variable quantities of at least two 

 defined masses; Mediterranean Water and 

 North Atlantic Deep Water. Wust (1936) called 

 this intermediate mass Upper North Atlantic 

 Deep Water in his discussion of the "Meteor" 

 data, and Defant (1961, p. 692) constructed a 

 standard curve (T-S) to show the percentage 

 of Mediterranean Water present in the mass. 

 The form of the T-S curves constructed from 

 data collected on ECHO (figs. 45-57) clearly 

 showed the influence of Mediterranean Water, 



