Interannual to decadal variability within and across the major Eastern Boundary Upwelling Systems

Abstract

Climate variability and climate change in Eastern Boundary Upwelling Systems (EBUS) affect global marine ecosystems services. We use passive tracers in a global ocean model hindcast at eddy-permitting resolution to diagnose EBUS low-frequency variability over 1958–2015 period. The results highlight the uniqueness of each EBUS in terms of drivers and climate variability. The wind forcing and the thermocline depth, which are potentially competitive or complementary upwelling drivers under climate change, control EBUS low-frequency variability with different contributions. Moreover, Atlantic and Pacific upwelling systems are independent. In the Pacific, the only coherent variability between California and Humboldt Systems is associated with El Niño Southern Oscillation. The remaining low-frequency variance is partially explained by the North and South Pacific expressions of the Meridional Modes. In the Atlantic, coherent variability between Canary and Benguela Systems is associated with upwelling trends, which are not dynamically linked and represent different processes. In the Canary, a negative upwelling trend is connected to the Atlantic Multi-decadal Oscillation, while in the Benguela, a positive upwelling trend is forced by a global sea level pressure trend, which is consistent with the climate response to anthropogenic forcing. The residual variability is forced by localized offshore high sea level pressure variability.

Long-Term Changes of Particle Flux in the Canary Basin Between 1991 and 2009 and Comparison to Sediment Trap Records Off Mauritania

“…Bakun (1990) and Bakun et al (2010Bakun et al ( , 2015 proposed a scenario of a general intensification of coastal upwelling due to increasing pressure gradients and wind fields associated with global warming. This hypothesis is under discussion and differing findings were recently summarized by Garcìa-Reyes et al (2015); Bonino et al (2019), and Sylla et al (2019). Bonino et al (2019) stressed that each EBUEs is unique in terms of forcings and climate variability and that the Canary Current (CC) system reveals a negative trend in upwelling intensity.…”

“…This hypothesis is under discussion and differing findings were recently summarized by Garcìa-Reyes et al (2015); Bonino et al (2019), and Sylla et al (2019). Bonino et al (2019) stressed that each EBUEs is unique in terms of forcings and climate variability and that the Canary Current (CC) system reveals a negative trend in upwelling intensity. Even the various sub-systems of the EBUEs defined by Cropper et al (2014; Figure 1) could react differently to global warming (Lathuilière et al, 2008;Arístegui et al, 2009;Sydeman et al, 2014;Garcìa-Reyes et al, 2015;Bonino et al, 2019).…”

“…Bonino et al (2019) stressed that each EBUEs is unique in terms of forcings and climate variability and that the Canary Current (CC) system reveals a negative trend in upwelling intensity. Even the various sub-systems of the EBUEs defined by Cropper et al (2014; Figure 1) could react differently to global warming (Lathuilière et al, 2008;Arístegui et al, 2009;Sydeman et al, 2014;Garcìa-Reyes et al, 2015;Bonino et al, 2019). A progressive warming and decreasing productivity over the last two decades was suggested for the CC-EBUEs as a whole (Arístegui et al, 2009).…”

Wind variability in the Canary Current during the last 70 years

“…However, the results of the correlation analysis between wind intensity and the AMO index seemed more complex. Bonino et al (2019) observed different climatic features related to the different EBUS worldwide. Specifically, they found a negative upwelling trend connected to the low frequency of the AMO index in the Canary Current System.…”

“…Recently, Bonino et al (2019) found sharp differences in Atlantic and Pacific upwelling areas, highlighting the uniqueness of each EBUS and observing a negative upwelling trend connected to the low frequency of the Atlantic Multidecadal Oscillation (AMO) in the Canary Current System. Therefore, the negative trend observed could be the result of the long-term variability of the AMO index.…”