We found a unique diel pattern with extremely high pH and low pCO2 levels across a diel cycle occurred repeatedly in four different seasons within the seagrass meadows of the inner lagoon (IL) on Dongsha Island. We proposed that this distinct diel pattern in pH and pCO2 could be associated with the enhancement of total alkalinity (TA) production coupled to carbonate sediment dissolution in a semienclosed lagoon. The confinement of the IL may hamper water exchange and seagrass detritus export to the adjacent open ocean, which may result in higher organic matter loading to the sediments, and longer residence time of the water in the IL, accompanied by microbial respiration (both aerobic and anaerobic) that may reduce carbonate saturation level to drive carbonate dissolution and thus TA elevation, thereby forming such a unique diel pattern in carbonate chemistry (i.e. a “super” blue carbon factory). These findings highlight the importance of considering TA production through metabolic carbonate dissolution when evaluating the potential of coastal blue carbon ecosystems to buffer ocean acidification and to absorb atmospheric CO2, which provide a very valuable theoretical proposition for conserving and restoring seagrass meadows as a promising strategy for climate change mitigation.

Primary Presenter: Wen-Chen Chou, National Taiwan Ocean University (wcchou@mail.ntou.edu.tw)

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