Greenhouse Warming Weakens the Seasonal Cycle of the Eastern Boundary Upwelling

The response of upwelling in the eastern boundary upwelling systems (EBUSs) to anthropogenic climate change has attracted much scientific attention due to its core role in nourishing marine ecosystems. A decade-old hypothesis suggests that greenhouse warming may intensify upwelling-favorable winds and subsequently the upwelling in EBUSs, but the impact of greenhouse warming on the seasonal cycle of upwelling remains unknown. Using the recent generation of global climate simulations under a high carbon emission scenario, we show a universal weakening of the upwelling seasonal cycle in the major EBUSs. This is mainly ascribed to the projected weakened seasonal cycle of the upwelling-favorable winds. In addition, long-term changes in geostrophic transport exert a nonnegligible contribution to the changes in the upwelling seasonal cycle. Our study suggests that the upwelling in the EBUSs is likely to have a more complicated response to greenhouse warming than previously thought.