STATE OF THE CALIFORNIA CURRENT 2011-2012: ECOSYSTEMS RESPOND TO LOCAL FORCING AS LA NINA WAVERS AND WANES

Abstract

The state of the California Current System (CCS) since spring 2011 has evolved in response to dissipation of La Nina through spring and summer, resurgence of cooler La Nina conditions in fall and winter, and finally a transition towards ENSO-neutral conditions in spring 2012. The resurgence of La Nina was uneven, however, as indicated by variable responses in broad climate indices such as the Pacific Decadal Oscillation and the multi-variate ENSO index, and by latitudinal variability in the timing, strength, and duration of upwelling relative to climatological means. Across the CCS, various measures of ecosystem productivity exhibited a general decline in 2011 relative to 2010, but the magnitude of these declines varied substantially among taxa. Available observations indicate regional variability in climate forcing and ecosystem responses throughout the CCS, continuing a pattern that has emerged with increasing clarity over the past several years. In 2011-12, regional variability was again a consequence of southern regions exhibiting a relatively mild response to climate forcing, in this case tending towards climatological means, while northern regions showed somewhat greater effects of delayed or weaker-than-normal upwelling. In addition to the effects of local and basin-scale forcing, long-term observations off southern California show declines in dissolved oxygen and increases in nutrient concentrations in waters below the mixed layer, trends that are consistent with recent predictions of how global warming will affect the characteristics of upwelling source waters in the CCS. Such trends must be accounted for more comprehensively in ongoing assessment of the state of the California Current and its responses to environmental forcing. At the time of writing, tropical conditions are ENSO neutral and forecast to transition into El Nino in late 2012. This, combined with unusually high abundances of diverse gelatinous taxa throughout much of the CCS during spring 2012, suggests that the ongoing evolution of the state of the California Current might take a particularly unusual path in the coming year.