Intensification and spatial homogenization of coastal upwelling under climate change

Abstract

The timing and strength of wind-driven coastal upwelling along the eastern margins of major ocean basins regulate the productivity of critical fisheries and marine ecosystems by bringing deep and nutrient-rich waters to the sunlit surface, where photosynthesis can occur. How coastal upwelling regimes might change in a warming climate is therefore a question of vital importance. Although enhanced land-ocean differential heating due to greenhouse warming has been proposed to intensify coastal upwelling by strengthening alongshore winds, analyses of observations and previous climate models have provided little consensus on historical and projected trends in coastal upwelling. Here we show that there are strong and consistent changes in the timing, intensity and spatial heterogeneity of coastal upwelling in response to future warming in most Eastern Boundary Upwelling Systems (EBUSs). An ensemble of climate models shows that by the end of the twenty-first century the upwelling season will start earlier, end later and become more intense at high but not low latitudes. This projected increase in upwelling intensity and duration at high latitudes will result in a substantial reduction of the existing latitudinal variation in coastal upwelling. These patterns are consistent across three of the four EBUSs (Canary, Benguela and Humboldt, but not California). The lack of upwelling intensification and greater uncertainty associated with the California EBUS may reflect regional controls associated with the atmospheric response to climate change. Given the strong linkages between upwelling and marine ecosystems, the projected changes in the intensity, timing and spatial structure of coastal upwelling may influence the geographical distribution of marine biodiversity.

Under Pressure: Climate Change, Upwelling, and Eastern Boundary Upwelling Ecosystems

“…In particular, it is predicted that global warming will impact atmospheric pressure gradients and hence the coastal winds that cause upwelling (Bakun, 1990;Bakun et al, 2015). Recent observations (Sydeman et al, 2014a) generally support this notion, and global model projections suggest intensification of regional coastal winds during the twenty-first century Wang et al, 2015).…”

“…Projections for the Humboldt Goubanova et al, 2011;Echevin et al, 2012;Belmadani et al, 2014;Rykaczewski et al, 2015;Wang et al, 2015), Benguela (Jury and Courtney, 1995;Rykaczewski et al, 2015;Wang et al, 2015), and Iberian Systems suggest future intensification of upwelling winds Casabella et al, 2014;Lopes et al, 2014;Rykaczewski et al, 2015;Wang et al, 2015). In contrast, the California System projections show non-significant or decreasing trends (Mote and Salathé, 2010;Rykaczewski et al, 2015;Wang et al, 2015).…”

Major impacts of climate change on deep-sea benthic ecosystems

“…Along canyon-cut margins (e.g., the western Mediterranean), warming may additionally reduce density-driven cascading events, leading to decreased organic matter transport to the seafloor (Canals et al, 2006), though this very process is also likely to reduce physical disturbance at the seafloor. Greenhouse warming will also increase temperature differentials between land and oceans, and intensify wind-driven upwelling in eastern boundary currents, stimulating photosynthetic production at the surface (Bakun, 1990;Bakun et al, 2015;Wang et al, 2015). However, this new production will ultimately start to decay as it sinks and increase biogeochemical drawdown of O 2 .…”

“…However, this new production will ultimately start to decay as it sinks and increase biogeochemical drawdown of O 2 . Upwelling will also bring low-O 2 , high-CO 2 water onto the shelf and upper slope (Bakun, 1990;Feely et al, 2008;Bakun et al, 2010;Sydeman et al, 2014;Wang et al, 2015). Increased levels of precipitation on land will also alter terrestrial inputs, including sediments and organic debris, nutrients, and contaminants (Jaedicke et al, 2009;Caroletti and Barstad, 2010) that may smother seafloor sediments, and alter the trophic ecology of deep-sea habitats situated close to land Wing, 2007, McLeod et al, 2010).…”

A carbon for every nitrogen

“…Climate change is also predicted to intensify the upwelling that supplies deep, nutrient-rich waters to the surface ocean (18,19). Massive quantities of the nitrogen applied by modern agriculture are subsequently exported to the oceans via rivers and atmospheric transport (20).…”