Physical-Ecological Response of the California Current System to ENSO events in ROMS-NEMURO

We analyze the bottom-up El Niño/Southern Oscillation (ENSO) driven physical-biological response of the California Current System (CCS) in a high-resolution, “eddy-scale” ocean model with multiple classes of phytoplankton and zooplankton forced with observed winds over the time period 1959–2007. The response of the sea surface temperature anomalies over the CCS is asymmetrical, with La Niña events being more consistently cold than El Niño events are consistently warm, which is in agreement with previous studies. The biogeochemical and ecological response is represented by ENSO composite anomalies, lag correlations with an ENSO index, and histograms for ENSO years. The results show trophic level interactions during El Niño and La Niña events in which the larger components (diatoms, euphausiids, and copepods) are suppressed in the coastal upwelling zones during El Niño, while the smaller components (flagellates and ciliates) are enhanced. In addition, standing eddies of the CCS modulate the latitudinal structure of the ecological response to ENSO. The results point towards future research to understand how bottom-up changes may lead to variability of patterns in ecological response, including fish populations and top predators.