Abstract

The Humboldt Current System (HCS) is a highly productive and biophysically variable ecosystem. Spatial/temporal ecosystem variability is crucial to resource sustainability, which is further emphasized by climate change and other stressors. To explore the biological response to changes in inorganic nutrient inputs and upwelling event duration on the continental shelf off south-central Chile (~ 36° S), we analyzed a monthly time series of wind satellite data from 2003 to 2013, direct observations of oceanographic parameters and in situ experiments of primary productivity (PP) and community respiration (CR). Monthly time series of in situ PP from two coastal bays were also examined. The spatial and temporal variability of nutrients and chlorophyll was also assessed using a ROMS-PISCES coupled model and temporal/spatial chlorophyll variability was analyzed using SeaWiFS satellite data. The seasonal cycles of PP and community net metabolism (PP/CR) strongly depend on the interplay between precipitation and river runoff in winter and the upwelling of cold nutrient-rich water into the euphotic zone in spring-summer. A drop in freshwater input in the coastal zone since 2007 has resulted in lower Si:N ratios in the mixed layer, which has negatively affected PP and altered carbon fluxes. Furthermore, phytoplankton production and biomass have been negatively affected by the lengthening of upwelling events since 2009, which has likely enhanced the export of nutrients and organic matter offshore and weakened nearshore stratification. We discuss the implications of these findings on temporal and spatial variability for the management of small pelagic fisheries in the southern HCS.