Interdecadal Variability in the Southern Part of the California Current for the Last Century: Diatom Assemblages from Laminated Sediments in San Lázaro Basin

M.A Esparza Alvarez¹, J. C. Herguera¹, and C. B. Lange^2
1 CICESE, Ensenada, Mexico
² University of Concepción, Concepción, Chile

We report on a century long reconstruction with annual resolution from two box cores retrieved from 540m depth in the suboxic San Lázaro Basin in the southern part of the Baja California continental margin. The goal of this study is to assess the use of diatom species and assemblages as proxies for reconstructing the dynamic oceanography and climatology at a decadal scale in the transitional zone of the southern part of the California Current (CC). Two kinds of samples were analyzed independently: a) sieved samples > 38 µm, and b) non-sieved samples.

Principal components analysis of the relative abundances of diatoms in the sieved samples was used to select species that behave coherently through the record and presumably reflect the oceanographic and climatic variability. These factors were compared with the instrumental Sea Surface Temperature (SST) record. The results show that species showing with high relative abundances, such as Coscinodiscus oculus-iridis, the Azpetia group, the Coscinodiscus group, and Paralia sulcata, seem to reflect the oceanographic variability expressed in their correlations with SST and other oceanographic indices.

Diatom assemblage variability patterns in the non-sieved samples are mainly controlled by changes in two genera, Cyclotella and Chaetoceros spores. Relative abundances of Cyclotella share a bidecadal periodicity with the Pacific Decadal Oscillation indicating the high sensitivity of this genus to cool conditions in the CC, especially between 1947 and 1976. In contrast, maxima in the relative abundances of Chaetoceros spores are associated with extreme warmings of the California Current, observed during those years when a combination of a bidecadal warm state and strong El Niño events produce an anomalously high warming of its surface waters.