Delayed coastal upwelling along the U.S. West Coast in 2005: A historical perspective

The timing of the onset of coastal upwelling in spring and its intensity over the upwelling season are critical factors in the productivity and structure of the California Current ecosystem (CCE). We use an index of coastal upwelling to characterize physical forcing over the latitudinal extent of the CCE, and compare the evolution of the upwelling season in 2005 with previous years. The onset of coastal upwelling in 2005 in the northern California Current was delayed by 2–3 months. Upwelling was stronger than normal in the latter part of the upwelling season, allowing the cumulative upwelling to reach the climatological mean by fall. Although physical conditions were unusual in 2005, they were not unprecedented in the historical record. However, the timing and strength of coastal upwelling is a critical ecological factor, particularly for species whose life histories are closely tuned to the annual cycle. The unusual physical and biological conditions observed in spring 2005 illustrate the sensitivity of the CCE to possible future climate extremes.