Future biogeochemical changes in southern South China Sea from CMIP6 model projection

Abstract

The ongoing climate change has significant impacts on global ocean biogeochemistry. This study employs Coupled Model Intercomparison Project Phase 6 Earth System Models under Shared Socioeconomic Pathways (SSPs) scenarios SSP2-4.5, SSP3-7.0, and SSP5-8.5 to investigate the future projection of biogeochemical changes in the southern South China Sea (SCS) from 2015 to 2100. The focus is on projected changes in Sea Surface Temperature (SST) and seven important biogeochemical variables, including Chlorophyll, Phytoplankton, integrated Primary Production, Oxygen, Nitrate, Phosphate, and pH. The results consistently indicate significant warming of 1 to 3 °C at the end of 21st century across all scenarios in southern SCS region, potentially leading to cascading consequences for marine ecosystems and fisheries. The projected increases in SST induce declines in dissolved Oxygen levels about − 3 to -8 mmol m-3 and ocean acidification about − 0.1 to -0.4 units, posing a multifaceted threat to this crucial fishing ground. This intensified warming is driven by the weakening of surface wind speeds and the strengthening of upper-ocean stratification, which simultaneously contribute to reductions in nutrient availability and productivity in the southern SCS. This projection assessment provides valuable insights into the anticipated biogeochemical shifts in the southern SCS under various climate scenarios, offering a vital foundation for understanding the adverse effects of climate change on the southern SCS ecosystems and ensuring its long-term sustainability.