Winter and summer upwelling modes and their biological importance in the California Current Ecosystem

Abstract

Abstract Analysis of monthly coastal upwelling intensities revealed two seasonal and biologically relevant upwelling ‘modes’in the California Current Ecosystem (CCE). The first mode reflected upwelling during the summer months and wascharacterized by low-frequency (multidecadal) processes, including significant (Po0.01) linear trends at somelatitudes. In contrast, the second mode reflected wintertime upwelling and was defined by higher-frequencyvariability associated with the North Pacific High and El Nin˜o Southern Oscillation events. These modes werecompared with multidecadal time series of splitnose rockfish (Sebastes diploproa) otolith growth, yelloweye rockfish(S. ruberrimus) otolith growth, Chinook salmon (Oncorhynchustshawytscha) scale growth, and indices of Cassin’s auklet(Ptychoramphus aleuticus) and common murre (Uria aalge) reproduction in the central-northern CCE. In redundancyand correlation analyses, salmon growth and Cassin’s auklet fledgling success associated with the summer upwellingmode while all other time series associated with the winter upwelling mode, indicating that CCE biology wasdifferentially sensitive to these seasonal upwelling patterns. Thus, upwelling occurred in unrelated seasonal modeswith contrasting trends, atmospheric forcing mechanisms, and impacts on the biology of the CCE, underscoring theimportance of seasonality when evaluating ecosystem response to climate variability and change.