Stratification changes and upwelling efficiency in Southern California Current

Hey-Jin Kim, Art Miller, Doug Neilson, and John McGowan
Scripps Institution of Oceanography, University of California San Diego

California current System (CCS) is highly variable and very productive. Many physical processes interact with various temporal and spatial scales, and they interact with the marine ecosystem. Long-term changes of the biological response to physical climate forcing are one of the main issues of interest, because the nonlinear ecosystem may not be linearly related to the persistent environmental disturbances (Hsieh et al., 2005). Roemmich and McGowan (1995) showed very unique observations of long-term physical-biological interaction in Southern California current and suggested that surface warming forced increased stratification, which capped the cold nutrient-rich upwelling cell, and consequently resulted in 70 % decrease in macrozooplankton biomass in the Southern California current. However, the linkage between stratification changes and zooplankton biomass is still not well understood. This study analyzes patterns of long-term stratification changes quantitatively in terms of mixed layer depth and thermocline depth with the in-situ dataset of 55 year CalCOFI (California Cooperative Oceanic Fisheries Investigations), and examines the upwelling efficiency and the primary production related to the stratification changes by ROMS.