Marisol García-Reyes

Climate change and wind intensification in coastal upwelling ecosystems

Strong winds, upwelling, and teeming shores Climate warming has produced stronger winds along some coasts, a result of growing differences in temperature and pressure between land and sea. These winds cause cold nutrient-rich seawater to rise to the surface, affecting climate and fueling marine productivity. Sydeman et al. examined data from the five major world regions where upwelling is occurring. Particularly in the California, Humboldt, and Benguela upwelling systems, winds have become stronger over the past 60 years. These regions represent up to a fifth of wild marine fish catches and are hot spots of biodiversity. Science, this issue p. 77 Increasing greenhouse gas concentrations have caused windier conditions in most major coastal upwelling regions. In 1990, Andrew Bakun proposed that increasing greenhouse gas concentrations would force intensification of upwelling-favorable winds in eastern boundary current systems that contribute substantial services to society. Because there is considerable disagreement about whether contemporary wind trends support Bakun’s hypothesis, we performed a meta-analysis of the literature on upwelling-favorable wind intensification. The preponderance of published analyses suggests that winds have intensified in the California, Benguela, and Humboldt upwelling systems and weakened in the Iberian system over time scales ranging up to 60 years; wind change is equivocal in the Canary system. Stronger intensification signals are observed at higher latitudes, consistent with the warming pattern associated with climate change. Overall, reported changes in coastal winds, although subtle and spatially variable, support Bakun’s hypothesis of upwelling intensification in eastern boundary current systems.

Anticipated Effects of Climate Change on Coastal Upwelling Ecosystems

Ecosystem productivity in coastal ocean upwelling systems is threatened by climate change. Increases in spring and summer upwelling intensity, and associated increases in the rate of offshore advection, are expected. While this could counter effects of habitat warming, it could also lead to more frequent hypoxic events and lower densities of suitable-sized food particles for fish larvae. With upwelling intensification, ocean acidity will rise, affecting organisms with carbonate structures. Regardless of changes in upwelling, near-surface stratification, turbulent diffusion rates, source water origins, and perhaps thermocline depths associated with large-scale climate episodes (ENSO) maybe affected. Major impacts on pelagic fish resources appear unlikely unless couples with overfishing, although changes toward more subtropical community composition are likely. Marine mammals and seabirds that are tied to sparsely distributed nesting or resting grounds could experience difficulties in obtaining prey resources, or adaptively respond by moving to more favorable biogeographic provinces.

Poleward displacement of coastal upwelling‐favorable winds in the ocean's eastern boundary currents through the 21st century

Upwelling is critical to the biological production, acidification, and deoxygenation of the oceans major eastern boundary current ecosystems. A leading conceptual hypothesis projects that the winds that induce coastal upwelling will intensify in response to increased land-sea temperature differences associated with anthropogenic global warming. We examine this hypothesis using an ensemble of coupled, ocean-atmosphere models and find limited evidence for intensification of upwelling-favorable winds or atmospheric pressure gradients in response to increasing land-sea temperature differences. However, our analyses reveal consistent latitudinal and seasonal dependencies of projected changes in wind intensity associated with poleward migration of major atmospheric high-pressure cells. Summertime winds near poleward boundaries of climatological upwelling zones are projected to intensify, while winds near equatorward boundaries are projected to weaken. Developing a better understanding of future changes in upwelling winds is essential to identifying portions of the oceans susceptible to increased hypoxia, ocean acidification, and eutrophication under climate change.

Six centuries of variability and extremes in a coupled marine-terrestrial ecosystem

Rings of ocean upwelling Coastal upwelling along the coast of California has become more variable than during nearly any period in the past 600 years. Black et al. used a 576-year tree ring record to construct a record of wintertime climate along the California coast. Because wintertime climate and coastal upwelling are so closely linked there, they were able to determine that upwelling variability has increased more over the past 60 years than for all but two intervals during that time. The apparent causes of the recent trend appear to be unique, resulting in reduced marine productivity and negative impacts on fish, seabirds, and mammals. Science, this issue p. 1498 Winter upwelling along the Pacific coast of North America became unusually variable during the 20th century. Reported trends in the mean and variability of coastal upwelling in eastern boundary currents have raised concerns about the future of these highly productive and biodiverse marine ecosystems. However, the instrumental records on which these estimates are based are insufficiently long to determine whether such trends exceed preindustrial limits. In the California Current, a 576-year reconstruction of climate variables associated with winter upwelling indicates that variability increased over the latter 20th century to levels equaled only twice during the past 600 years. This modern trend in variance may be unique, because it appears to be driven by an unprecedented succession of extreme, downwelling-favorable, winter climate conditions that profoundly reduce productivity for marine predators of commercial and conservation interest.

Satellite sea surface temperatures along the West Coast of the United States during the 2014–2016 northeast Pacific marine heat wave

From January 2014 to August 2016, sea-surface temperatures (SSTs) along the Washington, Oregon, and California coasts were significantly warmer than usual, reaching a maximum SST anomaly of 6.2 °C off southern California. This marine heat wave occurred alongside the Gulf of Alaska marine heat wave, and resulted in major disturbances in the California Current ecosystem and massive economic impacts. Here, we use satellite and blended reanalysis products to report the magnitude, extent, duration, and evolution of SSTs and wind stress anomalies along the west coast of the continental United States during this event. Nearshore SST anomalies along the entire coast were persistent during the marine heat wave, and only abated seasonally, during spring upwelling-favorable wind stress. The coastal marine heat wave weakened in July 2016 and disappeared by September 2016.

Integrated Assessment of Wind Effects on Central California’s Pelagic Ecosystem

Ecosystem-based management requires integrated physical studies on biological functions. In this study, we hypothesized that seasonal variation in upwelling-favorable winds has differential influences on species of the central California Current pelagic ecosystem. To test this hypothesis, we developed multivariate indicators of upwelling and species’ responses using wind and sea surface temperature (SST) data from buoys and growth and reproductive data for 11 species of fish and seabirds. From previous work, we predicted that winds and SST could be decomposed into winter and spring/summer ‘modes’ of variability, but only a single mode of “winter/spring” environmental variability was observed. We attribute this difference from expectations to the local and shorter-term measurements of winds and SST used in this study. Most species responded to winds and SST variability similarly, but SST was a better predictor of most biological responses. Both SST and wind were better predictors than the traditional upwelling index. Notably, Pacific sardine (Sardinops sajax) was disassociated with the other biotic measurements and showed no relationships with coastal upwelling. The multivariate indicators developed here are particularly appropriate for integrated ecosystem assessments of climatic influences on marine life because they reflect both structure and processes (upwelling and timing/growth/productivity) known to determine functions in marine ecosystems.