Based on over 300,000 individual measurements, temporal and spatial variations in diatom abundances and related atmospheric and oceanic variables have been investigated for two locations near the coast of southern California. Time scale of periods investigated ranged from days to 10 years; variability over centuries can be reconstructed from climate records. The results of principal component analysis based on weekly averages indicated that eigenvectors at Scripps and Pt. Hueneme piers, nearly 200 km apart, were similar; removal of seasonal cycles (by calculating anomalies) did not significantly alter these eigenvectors. Principal components derived from matrices based on weekly averages of 20, 23, and 65 species of diatoms have significant inverse correlations with sea-surface temperature anomalies. Based on 3-month (seasonal) averages, the abundance of several species of diatoms respond to climatic fluctuations as defined by changes in sea-surface temperature, air temperature, sea level and alongshore wind stress.