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Effect Of The 1997-98 El Niņo On Chlorophyll And Primary Production Across The Central California Upwelling Zone: Temporal Evolution, Spatial Pattern, And Comparison To Climatology

Francisco P. Chavez, J. Timothy Pennington, and Reiko P. Michisaki


Cruises, sample collection and processing. Approximately quarterly, 'Studies of Ecological and Chemical Responses to Environmental Trends' (SECRET), cruises have occupied 11 stations on CalCOFi Line 67 from 0-275 km offshore over the period March 1997 through the present (14 cruises; Figure 1). Additionally, time series cruises conducted at 2-3 week intervals have been undertaken from 0-55 km offshore over the period 1988 through the present (Figure 1). A suite of physical, chemical and biological measurements including chlorophyll and primary production are routinely taken on these cruises; sample collection and processing methods are described in detail by Pennington and Chavez (in press).

Data processing. Chlorophyll and primary production values from the 0-275 km cruises were grouped by oceanographic season (Nov, Dec, Jan=Davidson; Feb, Mar, Apr=Early Upwelling; May, Jun, Jul=Late Upwelling; Aug, Sep, Oct=Oceanic) and contoured with respect to depth and distance offshore (Figures 2 and 3). Chlorophyll and productivity data from ‘PEGASUS’ cruises occupying a similar transect over the period 1989-91 have been treated similarly and taken as a non-El Niņo ‘climatology’ (Figures 2 and 3). Anomalies were calculated (Table 1) for 0-10 m temperature and nitrate, chlorophyll and primary production (0 m, 100% light) values for the two cruise series’ for each season and for 3 spatial domains (0-50 km, 50-100 km and 100-200 km offshore).

Chlorophyll and primary production data from the 0-55 km cruises from 2 stations (C1 and M1) are plotted as Figures 4 and 5. In the top panels the data are daily-averaged (blue symbols), interpolated, and a running mean applied (red line). Standard deviations are represented with the black lines. For the middle panels anomalies were calculated by differencing the daily averaged, interpolated values from mean values, where mean values were calculated for each 14 day period. El Niņo comparisons (bottom panels) of surface data were constructed by plotting (1) the 1989-98 climatology, (2) the 1992 through 1993 El Niņo, (3) the 1997 through 1998 El Niņo. Table 2 shows anomalies for 0-55 km cruise stations, processed and presented in the same manner as in Table 1.

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Last Updated: 07 June, 2002