ABSTRACT

The integrated effects of photosynthesis-respiration and precipitation-dissolution of CaCO₃ on the partial pressure of carbon dioxide in seawater (PCO₂) by the carbonate-producing biological activities (e.g., coral reefs, coccolithophorids) have been extensively debated. Here we document PCO₂ values inside and outside the lagoon of Majuro Atoll. The PCO₂ was enhanced by 27 μatm on average within the atoll relative to ocean values. Alkalinity-total CO₂ relationship in the lagoonal water indicates that calcification plays a major role in the net carbon cycle in this reef system while rapid turnover of organic matter results in no significant net air-sea flux. The data show that atoll- and barrier-type of coral reefs potentially work as a source of CO₂.