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A ten-year time series from Monterey Bay, California: Seasonal, interannual and long-term patterns

C O N C L U S I O N S

seawifs.gif (573896 bytes)Fig. 6. Monthly SeaWiFS composites for six months of 1998. Compare the El Niņo winter of 1997-1998 (January, top panel) with the La Niņa (?) winter of 1998-1999 (November, bottom panel).

There are clear examples of physical-biological coupling on seasonal and decadal scales. Surprisingly the interannual connections are not as clear. Seasonally the spring and early summer are periods of upwelling. The upwelling signal is evident in winds, currents, temperature, nitrate, chlorophyll, primary production and centric diatoms. During the late summer and early fall (the oceanic period) there are increases in temperature, a shoaling and intensification of the poleward undercurrent, decreases in nitrate concentration, chlorophyll and primary production, and a shift in species assemblages. A deeper mixed layer and minima in biological and chemical properties characterize the winter.

The long-term trend is for the ecosystem to change from the upwelling condition to a more oceanic condition. Temperatures are increasing, the poleward undercurrent is intensifying, subsurface nitrate concentration, chlorophyll and primary production are decreasing, and a shift in species assemblages like that observed in the seasonal cycle is occurring. The increase in temperature has been well documented but the other changes have only been hypothesized. Time series like the ones presented here are extremely rare yet they are required before an accurate assessment of changes associated with global change can be made. Based on ten years of data we have constructed a coherent story of how the ecosystem may be changing, however, much longer series are required to confirm this story.

Acknowledgements

We gratefully acknowledge the David and Lucile Packard Foundation for their generous funding and continued support. We thank the crews of the R/V Point Lobos, Point Sur, and New Horizon as well as the science support staff. The Pacific Fisheries Environmental Lab (PFEL) and the Navy Fleet Numerical Meteorological and Oceanographic Center (FNMOC) provided the upwelling indices and the USGS provided the wind data from buoy 46012.

References

Breaker, L. C., W. W. Broenkow (1994) The circulation of Monterey Bay and related processes. Oceanography and Marine Biology Annual Review 32, 1-64.

Chavez, F. P. (1996) Forcing and biological impact of onset of the 1992 El Nino in central California. Geophysical Research Letters, 23, 265-268.

Chavez, F. P., J. T. Pennington, R. Herlien, H. Jannasch, G. Thurmond and G. E. Friederich (1997) Moorings and drifters for real-time interdisciplinary oceanography. Journal of Atmospheric and Oceanic Technology, 14, 1199-1211.

Skogsberg, T. (1936) Hydrography of Monterey Bay, California. Thermal Conditions, 1929-1933. Transactions of the American Philosophical Society held at Philadelphia for Promoting Useful Knowledge, 29, 1-152.

Skogsberg, T. and A. Phelps (1946) Hydrography of the Monterey Bay, California Thermal Conditions, Part 2 (1934-1937). Proceedings of the American Philosophical Society, 90, 350-386.

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