FUTURE CHANGES OF PHYSICAL-BIOGEOCHEMISTRY (1990–2060) IN THE SOUTH CHINA SEA UNDER RCP8.5 CLIMATE CHANGE SCENARIO

The South China Sea (SCS), one of the world’s most productive and commercially valuable fishing grounds and vital coral reef systems is particularly vulnerable to climate-induced ocean changes. Rising temperatures, ocean acidification, shifts in salinity, and other environmental factors driven by climate change pose uncertain but potentially profound risks to human and natural systems in the region. This study focused on three upwelling zones in SCS, located between 100 ºE – 119 ºE and 0 ºN – 13 ºN, western SCS (Vietnam), southern SCS on the east coast of Peninsular Malaysia (ECPM), and eastern SCS (Sabah). Using a coupled physicalbiogeochemical model at ~ 7 km resolution under the RCP8.5 scenario, this study projects marine environmental changes from 1990 to 2060 to assess the impacts of climate change on nutrient dynamics and overall ocean health. Eight surface physical–biogeochemical parameters: SST, SSS, diatom, NO3, NH4, O2, microphytoplankton, and microzooplankton were observed across monsoonal (SWM & NEM) and decadal trends (1990 – 2060). The SCS recorded a regional SST increase of ~1.3°C and a salinity drop of over 0.3 psu throughout the study period. Biogeochemical parameters also showed declining trends, indicating potential shifts in primary productivity. Surface O2 concentrations significantly decreased (-10 mmol O2/m3 ), suggesting broader implications for ocean health. These biogeochemical declines were most pronounced in the western, eastern, and southern SCS, largely driven by rising SST and changes in wind patterns. This study highlights a significant warming of up to 5.2%, salinity decline exceeding -1.5%, and widespread reductions in phytoplankton and zooplankton biomass reaching -19.9% by mid-century. These environmental shifts are likely to impact marine biodiversity, disrupt small-scale fisheries, and pose risks to food security across the region. This study provides valuable insights into the changes of physical and biogeochemistry trends under climate change, supporting future adaptation strategies for ecosystem management and coastal resilience.