Delayed upwelling alters nearshore coastal ocean ecosystems in the northern California current

Abstract

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...

Recruitment of coastal fishes and oceanographic variability in central California

“…Larval tows conducted off the coast of central California by NOAA Fisheries recorded very few individuals of the BYO complex in early 2005 (S. Ralston, personal communication) suggesting that events during the winter months and/or early spring were most responsible for the failure of this complex. Interestingly the spring of 2005 was an anomalous year for oceanographic trans port processes in the northeast Pacific Ocean (Barth et al, 2007). Upwelling was delayed 1-3 months along regions of North America with increased surface water temperatures, low chloro phyll a levels and a redistribution of zooplankton communities (Schwing et al, 2006).…”

Biophysical interactions in the Cabo Frio upwelling system, southeastern Brazil

“…Changes in land-cover are causing alterations in the intensity and seasonality of upwelling that would likely impact both marine and terrestrial environments. A month's delay of favorable winds reduced concentration of nutrients, chlorophyll a and recruitment of barnacles and mussels in the California upwelling system (BARTH et al, 2007). Land use is increasing in the Cabo Frio region.…”

Influence of Basin‐ and Local‐Scale Environmental Conditions on Nearshore Production in the Northeast Pacific Ocean

“…However, the pattern is evident in multiple indicators (SSHa, upwelling index, and PAR), lending some credibility to possible mechanistic linkages. Negative relationships between growth and upwelling are particularly unexpected given the previously established linkages between cool, nutrient-rich surface waters and higher production (e.g., Barth et al 2007;Chavez and Messié 2009;Black et al 2011). The unexpected growth-upwelling relationship could be related to the development of nearshore fronts that prevent planktonic food resources from reaching nearshore food webs (Shanks and McCulloch 2003).…”

“…Winter conditions might highlight the importance of preconditioning the water column for production (Polovina et al 1995;Gargett 1997;Logerwell and Mantua 2003;Black et al 2011). Spring conditions and the timing of the spring transition are known to be important for nutrient replenishment (Lynn et al 2003), high levels of primary production (Hayward and Venrick 1998), and a sensitive phase for several marine animal populations in terms of recruitment, growth, and reproduction (Barth et al 2007;Shanks and Roegner 2007).…”

“…For instance, variations in primary production, recruitment of benthic invertebrates, zooplankton abundance, rockfish Sebastes spp. growth, and seabird reproduction occur when the onset of upwelling in the California Current is delayed, whether or not normal upwelling conditions prevail later in the summer (Barth et al 2007;Shanks and Roegner 2007;Black et al 2011). …”