Highlights
- Surface seawater Chl-a shows a generally stable trend with slight decline over 20 years.
- Limited CO2-driven Chl-a response detected over two decades.
- Light–nutrient–temperature co-limitation dominates phytoplankton growth in the SCS.
Abstract
The partial pressure of CO2 (pCO2) in surface seawater continues to increase with the rising atmospheric carbon dioxide (CO2). However, whether elevated pCO2 enhances marine primary productivity and its actual impact on Chl-a shows distinct regional variability. Using chlorophyll-a (Chl-a, from Ocean Colour Climate Change Initiative satellite data), combined with high-resolution pCO2 dataset, we analyzed the spatiotemporal variations of surface seawater Chl-a and their response to pCO2 in the South China Sea (SCS) from August 2002 to December 2022. We demonstrate that Chl-a concentrations are higher in coastal regions, lower in the central basin, peak in winter, and are lowest in spring. Over the past two decades, surface seawater Chl-a has exhibited a generally stable pattern with a slight declining tendency, with a faster decrease in nearshore waters (−0.00693 mg m−3·yr−1, −0.27 %) than in central open waters (−0.00123 mg m−3·yr−1, −0.60 %). In contrast, surface seawater pCO2 has increased steadily, with a more rapid rise in central open waters (1.44 μatm yr−1) compared to nearshore areas (0.496 μatm yr−1), accompanied by a concurrent warming trend, where sea surface temperature increased at rates of 0.0346 °C·yr−1 and 0.0408 °C·yr−1 in nearshore and central open waters, respectively. Partial correlation analysis indicates that light inhibition is the main factor constraining phytoplankton growth in the SCS, while carbon availability is not a key influencing factor for phytoplankton in this region. Rising pCO2, accompanied by climate change effects such as rising sea surface temperatures and enhanced water column stratification, may contribute to a weakening of surface seawater Chl-a in the SCS. Further studies are needed to evaluate its future under climate change.
Wang R., Li X., Song J., Wang Z., Zhong G., Yuan H. & Duan L., 2025. Surface seawater chlorophyll-a variability in the South China Sea: influence of pCO2 and co-varying environmental factors. Environmental Research 279(Part 1): 121808. doi: 10.1016/j.envres.2025.121808. Article (subscription required).
