Feedback Mechanisms Between Atmospheric and Oceanic Factors on Atmospheric CO₂ Concentration Over Tropical Coastal Waters

The carbon cycle process in coastal areas is essential in the Earth’s climate system. Atmospheric CO₂ concentration over the coastal waters can be influenced by CO₂ flux and various atmosphere–ocean parameters. Understanding these relationships is essential for modeling and assessing carbon storage control. This research investigates the differences in air-sea exchanges during the northeast and southwest monsoons and their impact on atmospheric CO₂ concentration over tropical coastal waters from 2016 until 2019. Throughout the study period, the coastal waters functioned as a carbon sink (–0.023 µmol m^–2 s^–1), with CO₂ flux more strongly influenced by sea surface salinity than water temperature and CO₂ solubility in water. The overall carbon uptake suggests a potential reduction in atmospheric CO₂ concentration, as CO₂ flux notably contributes to its levels. However, seasonal variability distinctly impacts CO₂ flux. During the southwest monsoon, the coastal waters act as a carbon source (0.006 µmol m^–2 s^–1), primarily influenced by lower water temperature and higher CO₂ solubility, contributing to a higher CO₂ emission. Conversely, during the northeast monsoon, the coastal waters act as a carbon sink (–0.051 µmol m^–2 s^–1), with a reduced CO₂ absorption, strongly affected by increased rainfall and lower sea surface salinity. Horizontal transport-induced changes in atmospheric CO₂ concentration can influence CO₂ flux through dilution effects, contributing to higher carbon sources during the southwest monsoon and lower carbon uptake during the northeast monsoon, particularly during the northeast monsoon characterized by the higher wind speed.