Biological production off Southern California is linked to climatic change

To obtain clues about how coastal primary production might be affected by interannual and interdecadal changes in climate, we studied marine laminated sediments from the center of the Santa Barbara Basin. We report here a large decrease in the flux of diatoms between the periods 1954–1972 and 1973–1986, by a factor of five, and sustained reductions from 1973 to 1978 by a factor of ten below the pre-1972 period. Planktonic foraminifera flux shows a consistent trend of decrease with lowest values from 1981 to 1984. On the whole, the 1954–1972 period is considerably cooler than the 1973–1986 period, over the entire North Pacific. The decrease in biological production in this coastal system is accompanied by an overall intensification of the Aleutian Low in the North Pacific over the past 14 years, providing for a weakening of the California Current, and an overall reduction of mixing and upwelling. The possibility that the low coastal production could provide positive feedback to global warming through reduction of CO₂-uptake, and its relation to the greenhouse effect is considered. On a shorter time-scale, the effects of El Niño phenomena are clearly seen in the sediments of this basin, as decreases in total diatom flux and increases in the relative abundance of certain warm-water diatoms.