Dynamics of CO₂ and CH₄ fluxes in Red Sea mangrove soils

Abstract. Red Sea mangroves have a lower carbon burial rate than the global average, whereby small greenhouse gas fluxes may offset a large proportion of carbon burial. Monthly soil core sampling was conducted across 2 years at two sites within a central Eastern Red Sea mangrove stand to examine carbon dioxide (CO₂) and methane (CH₄) fluxes under dry and inundated conditions. Fluxes were highly variable, characterized by a prevalence of low emissions punctuated by bursts of high emissions. At the landward site, average ± SE (median) flux from the soil-air interface was 3111 ± 929 (811) µmol CO₂ m⁻²d⁻¹ and 1.68 ± 0.63 (0.26) µmol CH₄ m⁻² d⁻¹ under light conditions, and 8657 ± 2269 (1615) µmol CO₂ m⁻²d⁻¹ and 0.84 ± 0.79 (0.59) µmol CH₄ m⁻² d⁻¹ under dark conditions. Average ± SE (median) sea-air fluxes were –55 ± 165 (-79) µmol CO₂ m⁻²d⁻¹ and 0.12 ± 0.23 (0.08) µmol CH₄ m⁻² d⁻¹ under light conditions, and 27 ± 48 (53) µmol CO₂ m⁻²d⁻¹ and 0.16 ± 0.13 (0.09) µmol CH₄ m⁻² d⁻¹ in dark conditions. The seaward site recorded higher CH₄ flux, averaging 18.7 ± 8.18 (1.7) and 17.1 ± 4.55 (7.7) µmol CH₄ m⁻² d⁻¹ in light and dark conditions. Mean fluxes offset 94.5 % of carbon burial, with a median of 4.9 % skewed by extreme variability. However, reported CO₂ removal by total alkalinity emission from carbonate dissolution greatly exceeded both processes and drives the role of these ecosystems as intense CO₂ sinks.