Recent 121-year variability of western boundary upwelling in the northern South China Sea

Coastal upwelling is typically related to the eastern boundary upwelling system, whereas the powerful southwest Asian summer monsoon can also generate significant cold, nutrient-rich deep water in western coastal zones. Here we present a sea surface temperature record (A.D. 1876-1996) derived from coral Porites Sr/Ca for an upwelling zone in the northern South China Sea. The upwelling-induced sea surface temperature anomaly record reveals prominent multidecadal variability driven by Asian summer monsoon dynamics with an abrupt transition from warmer to colder conditions in 1930, and a return to warmer conditions after 1960. Previous studies suggest the expected increase in atmospheric CO₂ for the coming decades may result in intensification in the eastern boundary upwelling system, which could enhance upwelling of CO₂-rich deep water thus exacerbating the impact of acidification in these productive zones. In contrast, the weakening trend since 1961 in the upwelling time series from the northern South China Sea suggests moderate regional ocean acidification from upwelling thus a stress relief for marine life in this region. Key Points 121-yr monsoon-induced upwelling intensity record was inferred from coral The upwelling record shows an anomalous weakening trend since 1961 AD This trend may moderate regional ocean acidification