Total alkalinity production in a mangrove ecosystem reveals an overlooked Blue Carbon component
Vincent Saderne, Marco Fusi, Timothy Thomson, Aislinn Dunne, Fatima Mahmud, Florian Roth, Susana Carvalho, Carlos M. Duarte
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.