California Sea Grant College Program

The diversity, wide ranging habitats, and endemism of diatoms and radiolarians make them useful biological indicators of physical oceanography. The unique varved sediment (yearly layers) of the Santa Monica and Santa Barbara Basins (SMB and SBB, respectively) in the Southern California Borderland permits analysis of the diatom and radiolarian record at an annual resolution. In addition to the high resolution record preserved in the sediment, present-day teleconnections suggest that climate variability at SBB is a sensitive indicator of aspects of much broader scale climate variability over the North Pacific/North American sector. The purpose of this study was to determine whether the microfossil fluxes to the Santa Monica and Santa Barbara Basin sediments reflect the physical oceanography of California Current System.

Sediment samples were taken from the two basins with Soutar box cores. These were subcored and X-rayed to aid in delimiting the varves. Sediment from the years 1954-86 was sampled at the varve boundaries and analyzed for their diatom and radiolarian content. Counts of several diatom indicator species and all radiolarian species were made and fluxes calculated (in No.(cm-2)(y-1)). These data were compared to temperature and salinity data taken off the California coast.

The analyses rendered two important findings. First, the relative proportions of radiolarian species was surprisingly stable through the 33 year record, even during two major El Niños. This suggests some degree of constancy, across a variety of climate regimes, in the water masses circulated in the California Current System. Second, the flux of radiolarians varies on a decadal scale, in correspondence to anomalous, low frequency fluctuations of several environmental parameters. For example, the radiolarian flux is highly correlated to the regional average SST off the California coast. The California coastal environment is affected by large scale atmospheric forcing, therefore it is possible that the radiolarian record will also provide a paleo-index of North Pacific atmospheric circulation variations. The shorter diatom record proved promising as a paleotemperature record, but too brief for more substantial conclusions.