November 1970 to 7 December 1970), 

 figure 4a, and occupation No. 52 by 

 USCGC INGHAM (25 January 1971 to 

 11 February 1971), figure 4b. During 

 the first occupation 10 stations were 

 analyzed for dissolved oxygen; during the 

 second occupation there were 19 stations. 



Surface values of dissolved oxygen aver- 

 aged around 5.15 ml/1 for occupation 49. 

 The oxygen minimum occurred between 

 600 meters and 800 meters, with Og values 

 around 4.0 ml/1. After the minimum, 2 

 values increased with depth and reached 

 a maximum of about 6 ml/1 around 1500 

 meters. 



Occupation No. 52 showed higher 

 surface values (average around 5.5 ml/1) 

 followed by a more rapid decrease with 

 depth to the O2 minimum layer between 

 about 500 meters and 650 meters. The 

 minimum value was about 3.60 ml/1. 

 Again, values increased with depth to 1500 

 meters after which values were nearly 

 constant with increasing depth at about 6 

 ml/1. 



Both sets of data showed a great sim- 

 ilarity below the oxygen minimum layer. 

 The greater surface values during occu- 

 pation 52, and the more shallow and 

 lower minimum values indicated greater 

 biological activity, both production and 

 consumption, during the later occupation. 



Temperatures were cooler during occu- 

 pation 52 than during occupation 49. 

 There was, however, a warming trend 

 between January and February 1971, 

 while temperatures decreased between 

 November and December 1970. Salinity 

 showed a similar pattern. The cooling 

 during the first occupation may have 

 resulted in a sinking of the surface waters, 

 causing a removal of producers and 

 nutrients, while the warming trend during 



the second occupation could have caused 

 an increase in productivity. 



ISOTHERMS 



The coolest surface temperatures pre- 

 sent at Ocean Station ECHO was about 

 17* C, figure 5. This isotherm varied in 

 depth between 460 meters (September 

 1967) and the surface (April 1970). During 

 the period where ECHO was continually 

 manned (starting in April 1968), the 

 minimum depth of the 17° C level was 

 reached in April, and on two occasions in 

 June. 



The greatest depth of this level usually 

 occurred in late summer, and or in late 

 winter. The former occurring due to 

 the isotherms being depressed due to 

 summer heating and the latter due to 

 winter cooling and mixing. There was 

 generally as sUght rise in depth of the 

 isotherm between the fall and winter 

 deep values. 



This pattern was generally followed by 

 all isotherms from 17° C to 5* C. There 

 were some minor exceptions to this, but 

 these exceptions generally occurred during 

 months where the isotherms made only 

 small migrations. For example, between 

 April and May 1968 the 17° C through 

 10 " C isotherms became shallower, while 

 the 9° C tlirough 5* C isotherms moved 

 to deeper levels. The most radical depar- 

 ture from this general uniformity was 

 between February and March 1970, where 

 the 16° C through 5° C isotherms moved 

 50 meters deeper, while the 17° C isotherm 

 rose from 275 meters to 80 meters. This 

 may have been a result of atmospheric 

 (temperature) effects, although such effects 

 usually did not appear below 200 meters. 



Since deep stations were not made with 



6 



