Calcification-driven CO(2) emissions exceed “Blue Carbon” sequestration in a carbonate seagrass meadow

Long-term “Blue Carbon” burial in seagrass meadows is complicated by other carbon and alkalinity exchanges that shape net carbon sequestration. We measured a suite of such processes, including denitrification, sulfur, and inorganic carbon cycling, and assessed their impact on air-water CO(2) exchange in a typical seagrass meadow underlain by carbonate sediments. Eddy covariance measurements reveal a consistent source of CO(2) to the atmosphere at an average rate of 610 ± 990 μmol m(−2) hour(−1) during our study and 700 ± 660 μmol m(−2) hour(−1) (6.1 mol m(−2) year(−1)) over an annual cycle. Net alkalinity consumption by ecosystem calcification explains >95% of the observed CO(2) emissions, far exceeding organic carbon burial and anaerobic alkalinity generation. We argue that the net carbon sequestration potential of seagrass meadows may be overestimated if calcification-induced CO(2) emissions are not accounted for, especially in regions where calcification rates exceed net primary production and burial.