Marine carbon dynamics in a coral reef ecosystem of Southern Taiwan

Abstract. The ocean is the planet’s largest carbon reservoir and plays a crucial role in regulating atmospheric CO₂ levels, especially in the face of climate change. In coral reef ecosystems, understanding the carbonate system is critical for predicting and mitigating the impact of ocean acidification on these vulnerable marine ecosystems, especially as atmospheric CO₂ concentrations continue to rise. This study measured pCO₂ over space and time in Nanwan Bay, a coral reef ecosystem in southern Taiwan, to identify factors that influence its variation. The results showed that mean surface water pCO₂ values varied seasonally, with values of 393.7 (±10.8), 406.3 (±16.1), 399.2 (±18.6), and 366.9 (±14.5) μatm in spring, summer, fall, and winter, respectively. These seasonal mean differences (ΔpCO₂) relative to atmospheric pCO₂ were 7.7 (±10.8), 29.3 (±16.1), 21.2 (±18.6), and -16.1 (±14.5) µatm, respectively. These findings suggest that the Nanwan Bay is a highly dynamic coral reef ecosystem, exhibiting both spatial and seasonal variability in carbon exchange. The carbonate system parameters of the surface water in this high-biodiversity, sub-tropical marine ecosystem was influenced not only by seasonal temperature variation but also by vertical mixing, intermittent upwelling, and biological effects.