Asynchronous Methane and Carbon Dioxide Fluxes Drive Temporal Variability of Mangrove Blue Carbon Sequestration

The climate benefit of blue carbon sequestered by mangrove forests can be partially offset by CH 4 emission, but this offset is rarely assessed using multi‐year high‐frequency measurements. Here, four‐year eddy covariance measurements were used to examine temporal patterns of CH 4 flux and its blue carbon offset (i.e., reduced climate benefit) in a subtropical estuarine mangrove in China. We found both diel and seasonal CH 4 fluxes were mainly driven by soil temperature and tidal activities, showing greater nighttime emission. On average, one‐tenth of CO 2 uptake was offset by CH 4 emission using the sustained‐flux global warming potential metric at a 20‐year time horizon, while this offset could vary over an order of magnitude due to asynchronous fluxes of CH 4 and CO 2 across diel and seasonal cycles. These results highlight the significant contribution of nighttime emission to mangrove CH 4 budget and the importance of asynchronous flux variations in assessing mangrove's climate benefit.