Enhanced Regional Variability of Seawater pCO₂ Under Human and Natural Interference in a Nearshore Coral Nature Reserve (Dongshan Island, China)

Abstract CO 2 signatures differ among locations, even within the same coastal habitat. However, the driving mechanism behind this variation is not well understood due to the presence of both human and natural stresses. This study examines seawater p CO 2 and its deviation from the regional average (defined as p CO 2 anomaly) during spring, summer, and winter at two contrasting zones (trial and core zones) of Dongshan coral habitat. The impact of solar, tidal, and biological cycles on p CO 2 anomaly is relatively small under the designed sampling scheme. Results show that there is a large positive p CO 2 anomaly in the turbid water of the trial zone during all studied seasons, while the large negative p CO 2 anomaly in the core zone only occurs during the summer upwelling season. This indicates that CO 2 signatures among locations may have seasonality. The physical and biological contributors to p CO 2 anomaly are then quantitatively revealed based on a first‐order Taylor decomposition and biological carbon metabolisms. The results suggest that organic carbon metabolism of marine phytoplankton dominated p CO 2 anomaly in all three seasons, while inorganic carbon metabolism also enlarged p CO 2 anomaly, especially during summer. Physical contributions were minor. Moreover, significant linear correlations between turbidity (related to local human activities), chlorophyll (related to coastal upwelling) and changes in dissolved inorganic carbon (induced by organic carbon metabolism) indicate human and natural influences on bioprocesses, which may enhance p CO 2 anomaly. Finally, the Dongshan coral habitat was estimated as a source of atmospheric CO 2 , with an annual efflux of approximately 50 t C.