Wind-driven coastal ocean upwelling supplies nutrients to the euphotic zone near the coast. Nutrients fuel the growth of phytoplankton, the base of a very productive coastal marine ecosystem [Pauly D, Christensen V (1995) Nature 374:255-257]. Because nutrient supply and phytoplankton biomass in shelf waters are highly sensitive to variation in upwelling-driven circulation, shifts in the timing and strength of upwelling may alter basic nutrient and carbon fluxes through marine food webs. We show how a 1-month delay in the 2005 spring transition to upwelling-favorable wind stress in the northern California Current Large Marine Ecosystem resulted in numerous anomalies: warm water, low nutrient levels, low primary productivity, and an unprecedented low recruitment of rocky intertidal organisms. The delay was associated with 20-to 40-day wind oscillations accompanying a southward shift of the jet stream. Early in the upwelling season (May-July) off Oregon, the cumulative upwelling-favorable wind stress was the lowest in 20 years, nearshore surface waters averaged 2°C warmer than normal, surf-zone chlorophyll-a and nutrients were 50% and 30% less than normal, respectively, and densities of recruits of mussels and barnacles were reduced by 83% and 66%, respectively. Delayed early-season upwelling and stronger late-season upwelling are consistent with predictions of the influence of global warming on coastal upwelling regions.climate variability ͉ coastal marine ecosystems ͉ coastal ocean upwelling ͉ marine ecology E quatorward winds along the eastern boundaries of the world's oceans drive offshore surface Ekman transport and the upwelling of cold, nutrient-rich water into the euphotic zone near the coast. These nutrient pulses stimulate high phytoplankton production, which, in turn, supports a rich coastal marine ecosystem and productive fisheries (1). Examples of such dynamics include the California Current, the Humboldt Current, the Benguela Current, and the Canary Current (2).The strength and extent of the seasonal cycle in upwellingfavorable winds varies along the U.S. west coast. In the northern California Current Large Marine Ecosystem (CCLME), there is a strong seasonal cycle with upwelling-favorable winds, the appearance of cold, saline, nutrient-rich water near the coast, and equatorward currents over the shelf occurring after a spring transition (3). Alongshore winds in the northern CCLME are more variable than those farther south because they are more frequently influenced by eastward-traveling Gulf of Alaska low-pressure systems. The intermittent cessation of upwelling-favorable winds is called relaxation and plays an important role in coastal circulation and the recruitment of marine organisms † † . The timing of the spring transition and the total amount of upwelling-favorable winds during the spring-summer upwelling season have a considerable impact on coastal ecosystem responses. Farther south in the CCLME, winds are more persistently upwelling-favorable and the transition to a more productive spring-su...
