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

Abstract

Abstract 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 CO 2 . 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 CO 2 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.