Total alkalinity production in a mangrove ecosystem reveals an overlooked Blue Carbon component

Mangroves have the capacity to sequester organic carbon (C-org) in their sediments permanently. However, the carbon budget of mangroves is also affected by the total alkalinity (TA) budget. Principally, TA emitted from carbonate sediment dissolution is a perennial sink of atmospheric CO2. The assessment of the TA budget of mangrove carbonate sediments in the Red Sea revealed a large TA emission of 403 +/- 17 mmol m(-2)d(-1), independent of light, seasons, or the presence of pneumatophores, compared to -36 +/- 10 mmol m(-2)d(-1)in lagoon sediment. We estimate the TA emission from carbonate dissolution in Red Sea mangroves supported a CO2 uptake of 345 +/- 15 gC m(-2)yr(-1), 23-fold the C-org burial rate of 15 gC m(-2)yr(-1). The focus on C-org burial in sediments may substantially underestimate the role of mangroves in CO(2)removal. Quantifying the role of mangroves in climate change mitigation requires carbonate dissolution to be included in assessments.