MALONE: RELATIVE IMPORTANCE OF NANNOPLANKTON AND NETPLANKTON 



O N D J 



O N D J 



Figure 2. — a. Vertical distribution of temperature (°C) 

 at CalCOFI 3 from October 1969 to February 1971. 

 b. Vertical distribution of NO3-N (yaM). 



Table 1. — Environmental factors monitored at the sur- 

 face, concurrently with measurements of productivity 

 and standing crop at CalCOFI station 3 in Monterey 

 Bay. 



Temper- 

 ature 



Salinity 



NO3-N 



Mixed Photic 

 layer zona 



28 Oct. 69 



2 Dec. 

 26 Feb. 70 



5 Mor. 

 10 Mar. 

 18 Mar. 



°C 



14.20 

 14.68 

 13.10 

 13.20 

 13 17 

 12.06 



33.51 

 33,39 

 32.68 

 32,99 

 32.98 

 33.11 



1.7 

 0.3 

 0.3 

 0.4 

 C.l 

 0.4 



li.M 



0.3 

 0.6 

 0,2 

 0.4 



30 

 30 

 50 

 30 

 25 

 15 



60 

 55 

 60 

 50 

 65 

 30 



face water of oceanic origin was found in the 

 Bay from October 1969 to mid-March 1970. The 

 intrusion of oceanic water and the general sub- 

 sidence of the water mass are evidenced by the 

 descending isotherms and nitrate isopleths, high 

 surface temperatures, and low salinities. Mixed 

 layer and photic zone depths were about 30 and 



60 m respectively, and NO3-N concentrations 

 were less than 0.5 fiM throughout most of the 

 photic zone. 



Upwelling was initiated in March as indicated 

 by the ascending isotherms and nitrate isopleths, 

 NO3-N concentrations in excess of 5.0 fiM over 

 the entire photic zone, low surface temperatures, 

 and high surface salinities. With the exception 

 of a minor intrusion of oceanic water late in July 

 and early August, upwelling continued uninter- 

 rupted into September with peaks in early April 

 and early September. "Mixed layer" depths 

 varied between and 30 m, and at no time ex- 

 ceeded the depth of the photic zone, which 

 ranged from 15 to 45 m. 



From September through December the hy- 

 drography of the Bay was confused and neither 

 oceanic nor upwelling conditions ever predomi- 

 nated. Weak upwelling surges bracketed by in- 

 fluxes of oceanic water occurred during late Oc- 

 tober and late November (Figure 2). Surface 

 NO3-N concentrations were variable (0.2 to 3.1 

 jLiM) reflecting the indecisiveness of the system. 

 Then, following a period of oceanic water during 

 December and early January, a strong upwelling 

 pulse occurred which was about as intense as 

 the upwelling during late March and early April 

 of the previous year. 



Hydrographically, three periods can be dis- 

 tinguished in the Bay during the period of this 

 study: 



1. A stable Oceanic Period from October 1969, 

 into March 1970, 



2. A stable Upwelling Period from March into 

 September, 



3. A "Mixed" Period from September through 

 December punctuated by a strong upwell- 

 ing pulse in January. 



The grazing pressure index declined during 

 the transition from oceanic to upwelling condi- 

 tions to a low of 0.03 in early April (Figure 3) . 

 Grazing pressure then increased rapidly during 

 the steady upwelling of June and July to an an- 

 nual maximum of 2.03 which was followed by 

 a gradual decline during the Mixed Period end- 

 ing with a sharp rise in late January to a peak 

 in early February. 



803 



