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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

I N T R O D U C T I O N

El Niņo is the dominant source of interannual ocean variability on sub-decadal to decadal time scales and has significant impact on the ocean's ecosystems (Barber and Chavez, 1986, Cane, et al., 1986). The physical effects of El Niņo (Rasmusson and Wallace, 1983) are most evident in the eastern Pacific (Barber and Chavez, 1983) where its influence can be detected from the tip of Chile to Alaska (Enfield and Allen, 1980; Norton and McLain, 1994).

The productivity and biogeochemical responses of equatorial Pacific ecosystems to the 1997-98 El Niņo have recently been described (Chavez et al., in press). At higher latitudes, the biological response of eastern boundary coastal upwelling systems to El Niņo still remains poorly understood (see Kudela and Chavez, in press). The productivity consequences of the large El Niņo of 1982-1983 were documented relatively well off Peru (Barber and Chavez, 1983,1986) but poorly off California. The weak El Niņo of 1991-1992 was better documented off California (Chavez, 1996; Lenarz et al. 1995).

Observations made off Peru in 1982-1983 (Barber and Chavez, 1983) and off California in 1992 (Chavez, 1996; MacFadyen, 1999 EPOC Poster) suggest that the normally highly productive upwelling zone may be compressed into a narrow nearshore band during El Niņo. Such spatial compression could have important consequences for (1) distribution of higher trophic level organisms (krill, clupeid fishes, salmon, whales) and their availability to fisheries, (2) spatial pattern of eventual deposition of productivity on the deep sea floor (see Pilskaln et al., 1996, and (3) potential aliasing of coastal measurements of the biological impact of El Niņo.

Here we describe the spatial and temporal evolution of the 1997-98 El Niņo in terms of chlorophyll and primary production, based on two cruise series’ off central California. Data from both cruise series are compared to climatologies constructed from cruisework during non-El Niņo years.

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Last Updated: 07 June, 2002