Spatial and interannual variability in mesoscale circulation in the northern California Current System

Abstract

We used wavelet analyses of sea surface height (SSH) from >13 years of satellite altimeter data to characterize the variability in mesoscale circulation in the northern California Current (35°N–49°N) and explore the mechanisms of variability. We defined “mesoscale” circulation as features, such as eddies and filaments, which have 50‐ to 300‐km length scales and 4‐ to 18‐week temporal scales. Fluctuations in SSH caused by such features were reflected in wavelet analyses as power (energy). Spatial and interannual variation in mesoscale energy was high. Energy was highest at ∼38°N, decreasing to the north and south. Between ∼43°N and 48°N, energy was low. Zonally, mesoscale energy was highest between ∼125°W and 129°W at latitudes south of 44°N; very little power occurred in the deep ocean west of 130°W. Energy peaked during summer/fall in most years. The primary climate signals were suppressed energy during La Niña and cold years and increased energy during El Niño events. Energy was not strongly linked to upwelling winds, but did correspond to climate indices, indicating that basin‐scale processes play a role in controlling mesoscale circulation. We hypothesize that climate affects mesoscale energy through changes in both potential and kinetic energy in the form of density gradients and coastal upwelling winds. The relationship between mesoscale circulation and climate was complex: no single climate, transport, or upwelling index explained the variability. These results are relevant to ecosystem dynamics and the global carbon cycle because mesoscale circulation features deliver nutrient‐rich water and coastal organisms from productive upwelling areas to the deep sea.