Coastal upwelling will intensify along the Baja California coast under climate change by mid-21st Century: Insights from a GCM-nested physical-NPZD coupled numerical ocean model

Abstract Wind-driven coastal upwelling along the eastern boundary currents sustains the ecosystem productivity in these systems by transporting deep nutrient-rich waters to the euphotic zone where photosynthesis can occur, generating one of the most productive ecosystems in the world. One of the most pressing concerns in oceanography is how coastal upwelling systems might respond to climate change. These systems are affected by two mechanisms associated with climate change which are opposing each other: the surface warming that increases the stratification of the water column and, as the Bakun hypothesis states, the intensification of coastal alongshore winds that could enhance the upwelling. The question is which of these mechanisms will dominate the coastal upwelling dynamics. This paper addresses this question for the coastal upwelling system along the western coast of the Baja California Peninsula, which comprises the southern part of the California Current System. A regional physical-biogeochemical coupled model, nested to a global circulation model (GFDL-CM3), is used to explore the response of primary production to future climate-change scenarios (RCP6.0 and RCP8.5) in this region. The results toward the year 2050 project an increase in cholophyll concentration during spring in both scenarios. During summer, when the highest temperatures are observed, an increase in chlorophyll is projected only within a narrow zone along the coast and a decrease in chlorophyll out of that narrow zone due to enhanced stratification in open ocean in the RCP6.0 scenario. In the RCP8.5 scenario, the strip with enhanced chlorophyll becomes wider due to stronger alongshore winds which enhance the nutrient supply into the upper levels over the continental shelf.