Diverse Responses of Upper Ocean Temperatures to Chlorophyll-Induced Solar Absorption Across Different Coastal Upwelling Regions

Abstract

Chlorophyll in phytoplankton absorbs solar radiation (SR) and affects the thermal structure and dynamics within upwelling regions. However, research on this process across global-scale coastal upwelling systems is still lacking. Here, we use a coupled ocean-biogeochemical model to investigate differing responses to chlorophyll-induced solar absorption between Pacific and Atlantic coastal upwelling regions. Chlorophyll-induced solar absorption leads to colder Pacific coastal upwelling but warmer Atlantic coastal upwelling. In the Pacific, the shading effect of the surface chlorophyll maximum leads to colder subsurface water, which is then upwelled, contributing to cooling. The more stratified upper ocean leads to shallower mixed layer depth, intensifying offshore transport and upwelling. In the Atlantic, the absorption of SR by the subsurface chlorophyll maximum causes warmer and weaker upwelling. The processes described, in turn, trigger positive feedback to ocean biogeochemistry and potentially interact with climate dynamics, underscoring the necessity to incorporate them into Earth system models.