FISHERY BULLETIN: VOL. 70, NO. 4 



WATER TEMPERATURES ON 

 EASTROPAC II 



Water temperatures were available at 1-m 

 intervals from the surface to about 750-m depth 

 for each station at which an STD was used for 

 determination of salinity and temperature. I 

 selected three depths for tabulation and study: 

 surface, 10 m, and 50 m. STD readings were 

 available for 347 of the 355 plankton stations 

 taken on ETP II. A chart of surface temper- 

 ature for ETP II will be included in the EAS- 

 TROPAC Atlas. 



To facilitate discussion of distributions of fish 

 larvae, I have found it convenient to divide the 

 EASTROPAC area into quadrants with the 

 north-south division at the equator and the east- 

 west division at long 100 °W. I will use these 

 divisions when discussing distribution of tem- 

 peratures on ETP II, except for separating out 

 a narrow band of water at the equator (lat 2°N 

 to 2°S). Within a quadrant the temperatures 

 are summarized by 5° latitude, except near the 

 equator (Table 4). 



In some parts of the ETP II pattern, the ther- 

 mocline was considerably deeper than 50 m, so 

 that the temperature at 50 m was similar to that 

 at the surface. At a few stations in the north- 

 east quadrant, where the thermocline was almost 

 at the surface, the temperature at 10 m was 5° 

 to 10° C lower than at the surface. At most sta- 

 tions in this quadrant the thermocline was con- 

 siderably shallower than 50-m depth, as attested 

 by marked differences in temperature between 



the surface and 50 m (Table 5). Mixed layer 

 depths on ETP II were illustrated in Blackburn, 

 Laurs, Owen, and Zeitzschel (1970) — Figure 7 

 on page 27. A brief summary of the tempera- 

 ture structure is given by quadrant. 



NORTHEAST QUADRANT, EXCEPT 

 WITHIN 2o LATITUDE OF EQUATOR 



Surface temperatures in this quadrant were 

 high, ranging between 25.4° and 29.8°C (av- 

 erage 27.2°C) , Temperatures at 10 m were usu- 

 ally the same or within ±0.5°C of the surface, 

 although 10 stations showed differences of more 

 than 1°C and 7 of those were 4.6° to 10.1°C 

 lower. These marked differences are indications 

 of very shallow thermoclines; five contiguous 

 Stations along long 88°W offshore from Pun- 

 tarenas, Costa Rica, had such near-surface 

 thermoclines. 



At most stations the thermocline was shal- 

 lower than 50 m; at 79 of 91 stations, the tem- 

 perature at 50 m was 5° to 15°C lower than at 

 the surface, and at half of these the temperature 

 was between 10° to 15°C lower at 50 m. 



NORTHWEST QUADRANT, EXCEPT 

 WITHIN 2° LATITUDE OF EQUATOR 



Surface temperatures in this quadrant, 24.8° 

 to 29.7°C (average 27.6°C), were similar to 

 those of the inshore quadrant. Highest surface 

 temperatures, averaging 28.3°C, were encoun- 



Table 4. — Range of temperatures at surface, 10 m, and 50 m summarized by 5° latitude or smaller intervals for 

 both offshore (long 100°-119°W) and inshore (coast to long 98°W) for EASTROPAC II. 



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