STA 

 



5E 3 

 381 CL/TON 



100 



^ 150 



200 



250 



5E 2 

 389 CL/TON 



5E I 

 394 CL/TON 



THERMOSTERIC ANOMALY (CL/TON) 

 150 200 250 300 350 



_iSQ_ 



^^—390 



320 



300 



160 



WARM SIDE 



MIDDLE 

 COOL SIDE 



-o a — 



-A— •*■ — 



- 200 



-7.8 KM- 



Figure 22. — Thermosterlc anomaly ( S j) profile and 5-p-depth curves for the second triplet (E) of hydrocasts at 

 front 5 (23 April 1961). c = cool side; m = middle; w = warm side; • = Nansen bottle depths In profile. 



one, at any rate) accumulates plankton, either 

 mechanically or by providing favorable condi- 

 tions for its increase. This opinion is backed 

 by only a few direct observations (Uda, 1938; 

 Knauss, 1957; King andHida, 1957, and others). 

 There was not enough time to make a thorough 

 study of the plankton distributionat front 5, and 

 our results do not all confirm the aggregation 

 hypothesis. We made three kinds of tow to 

 sample zooplankton: (1) oblique hauls to a depth 

 of about 300 m., except two inshore; (2) hori- 

 zontal hauls near the surface, both kinds being 

 made with a nonclosing net of 1 m. mouth 

 diameter; and (3) horizontal hauls, above, in, 

 and below the thermocline, simultaneously, 

 with Clarke-Bumpus (C-B) closing nets of 

 25.4 cm. mouth diameter. One kind of tow was 

 used to sample micronekton: an oblique haul 

 to about 100 m. depth with a 1.52- by 1.52-m. 

 square-mouthed net. Micronekton consists of 

 small organisms longer or wider (disregarding 

 antennae, etc.) than 5 cm., but less than 15 

 cm.; both these limits are arbitrary. Only fish 



present any difficulty in this assignment, and 

 they, not often. 



We made all hauls as nearly as possible 

 along an isotherm (warm, middle, or cool). 

 The isotherm desired was noted from the 

 thermograph, and the ship was stopped and 

 allowed to drift. It usually drifted along an 

 isotherm, and its direction of drift was used 

 for the tow. We checked the thermograph dur- 

 ing the tow to ensure that the haul did not 

 pass into water of undesired surface tempera- 

 ture while the ship steamed. 



Table 2 summarizes the results of zoo- 

 plankton and nekton net hauls. I have stand- 

 ardized catches to volume (ml.) per 1,000 m.-* 

 (lO^m.-^) of water strained. This standardiza- 

 tion is based on data from a flowmeter mounted 

 in the mouth of the zooplankton nets, but 

 is empirical for nekton net tows, being based 

 on a filtration coefficient of the 1.52- by 1.52- 

 m./net, on distance, and on duration of the 

 tow (Blackburn and associates, 1962). The two 

 main components of the catches are separated 



29 



