BEERS ET AL.: PLANKTON AND UPWELLING OFF PERU 



Table 2. — Vertical shear and stability in Patch 2. 



Stations 



Depth 

 (m) 



Vdsaild 

 frequency, 



N 



(10-3 sec-1 



Velocity 

 {cm sec — ' 



Verticol 



sheor 



00-3 sec-i) 



Richardson 

 number^ 



' Component velocities, u and v, are from current meter measurements and are positive to the east and north, 

 respectively. 



2 Ri , Ri = Richardson numbers using the east and north velocity components, respectively. 



^ The deepest observations ore used for reference and are shown with zero velocity. 



measured velocity of about 15 cm/sec was about 

 half that seen in this study around lat 11° S. 

 From the PISCO Cruise of the University of 

 Washington, April-May 1969, Smith et al. 

 (1971) were able to estimate upwelling in a 

 narrow coastal region near lat 15° S. They de- 

 termined the vertical velocity to average 2 X 

 10 ~2 cm/sec over the period of the investigation 

 and estimated it to decrease with increased 

 distance from shore so as to become zero at 20 km 

 offshore. 



PHYTOPLANKTON DYNAMICS IN THE 

 PATCHES 



Photosynthetic carbon assimilation measure- 

 ments (Table 3) showed that the phytoplankton 

 crop was physiologically active in both patches 

 throughout the periods of observation even 

 though the patches, as defined by their surface 

 characteristics, were gradually becoming more 

 difficult to recognize (see Figure 5). The de- 

 cline in the abundance of phytoplankters at the 



Table 3. — Phytoplankton standing crop as carbon, photosynthetic rate, specific growth rate, chlorophyll a and 

 carbon/chlorophyll a ratio for plankton patches off Peru, June 1969. (See Table 4 for positions of stations.) 



Static 



Euphotic 

 zone 

 depth 



Phytoplankton 



standing crop 



(g C/m2) 



Photosynthetic 



rate 

 (g C/mVday) 



Specific growth 



rate T/i) 

 (doublings/day) 



Chlorophyll , 

 (mg/m2) 



Ratio 

 carborVchl a 



(g/9) 



59 

 68 

 77 

 87 



14 June 1969 



15 June 1969 



16 June 1969 

 18 June 1969 



IB 

 28 

 30 

 42 



2.16 

 1.39 

 1.40 

 1.91 



1.19 

 0.83 

 1.09 

 1.01 



Value probobty low, judged from the high fi or low C/chI a ratio. 



0.64 

 0.68 

 0.83 

 061 



S0.3 

 45.7 

 39 



40.8 



42.8 

 30.4 

 36 

 46.7 



867 



