X 22 00 



Figure 25. — Temperature, salinity, and thermosterlc anomaly distribution across front 5 at the surface, as deter- 

 mined on BT pass no. 3(21 April 1961). See fig. 15 for corresponding vertical temperature distribution. 



in table 2, because I assume that zooplankton 

 could be aggregated by the front, whereas the 

 micronekton could not, though it might be 

 attracted to the front by the plankton. 



To determine whether the front was a focus 

 of organisms, ratios of standardized volumes 

 from one haul to the next across the front 

 have been given in table 2 (value for the warm 

 side set at unity). If the front aggregates 

 plankton, the volume in the middle should 

 greatly exceed that on either side. Significance 

 of differences has been taken as half or double 

 a given value, based on studies by Winsor and 

 WaLford (1936), Winsor and Clarke (1940), and 

 Silliman (1946), although their studies were of 

 variability in counts, not volumes. The present 

 author (unpublished) has obtained compar- 

 able results for volumes of crustacean zoo- 

 plankton, though for salps the confidence limits 

 are much wider. 



The sampling methods are standard and, with 

 respect to front studies, are open to criticism 

 for the following reasons: 



( 1 ) The oblique hauls sample water well below 

 the frontal zone (i.e., deeper than 120 m.). I 



Griffiths, R. C. "The variability of volumes of zooplank- 

 ton taken in oblique, paired, one-meter net hauls." 



believe, however, that contributions from below 

 the frontal zone are (1) relatively independent 

 of the front and not greater on one side than 

 on the other; and (2) relatively small, because 

 one set of hauls was taken at night when effects 

 due to vertical migration would be minimal, 

 and the other set was taken at dusk when these 

 effects would be tending to a minimum (i.e., 

 plankton mostly in upper 100 m.). 



(2) Oblique hauls on either side of the front 

 may sample parcels of water from the oppo- 

 site side, by virtue of the Z- shaped interface 

 (figs, 15, 19, and 20). This event is possible 

 (see cast profiles, figs. 19 and 20), but the 

 data show that the cool side has a higher stand- 

 ing crop than the warm side; such differences 

 would tend to dissappear if the haul on the 

 warm side were sampling a significant amount 

 of the cool water, or vice versa. 



We may suppose, then, that the catches of the 

 oblique hauls reflect fairly well the effect of 

 the front on the biota. Judging from the results 

 of the two sets of oblique hauls (A and F series), 

 zooplankters are concentrated in the front 

 (table 2). 



A similar conclusion might be drawn from 

 the results of the Clarke-Bumpus net tows 

 (5C1 - 3) above the thermocline, but these 



32 



