Abstract
AbstractMangroves have the capacity to sequester organic carbon (Corg) 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 Corg burial rate of 15 gC m−2 yr−1. The focus on Corg burial in sediments may substantially underestimate the role of mangroves in CO2 removal. Quantifying the role of mangroves in climate change mitigation requires carbonate dissolution to be included in assessments.
Highlights
Author Contribution Statement: VS and MF designed the study
Based on a review of carbonate burial and budgets in Blue Carbon sediments, we recently proposed that carbonate dissolution may be an important, but overlooked mechanism of CO2 removal in Blue Carbon habitats where carbonate is supplied from adjacent calcifying ecosystems, such as coral reefs and lithogenic carbonate deposits (Saderne et al 2019b)
We did not find an apparent seasonal pattern in our data (Fig. 2b), we found significant changes over time (p = 0.001; Table S1), which differed between sediment types and the time of the day
Summary
Author Contribution Statement: VS and MF designed the study. VS, MF, TT, AD, FR, and FM carried out field and laboratory work. Dissolution of CaCO3 could occur at the sediment-water column interface in Blue Carbon ecosystems, due to the acidification caused by the metabolic activity of the benthic fauna and flora, principally respiration at night (Rosentreter et al 2018; Saderne et al 2019a).
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