Capacity of Coastal Wetlands to Sequester Carbon Is Linked to Sea-Level Rise

Coastal wetlands (mangrove, saltmarsh, seagrass) sustain the highest rates of carbon sequestration per unit area of all natural systems, primarily due to comparatively high productivity and preservation of organic carbon within sedimentary substrates. However, the prospect of continued sequestration under rising sea-level is challenged by the possibility of drowning and erosion. We considered the relationship between sea-level rise and carbon accumulation in saltmarshes at a global scale, utilising a dataset of saltmarsh soil carbon to 1m depth at 345 settings on five continents. We analysed these cores in relation to sea-level trends over the previous two millenia. At a global scale, saltmarshes in coastlines exhibiting SLR over the late Holocene have, on average, 1.8 to 4.7 times higher soil carbon concentrations than those subject to a long period of isostatic and sea-level stability. Wetlands on a tectonically stable coastline undergoing relatively little isostatic adjustment were then selected to explore responses to contemporary eustatic acceleration in RSLR and rapid RSLR (using mine subsidence as a surrogate). Our results suggest that highly minerogenic coastal wetlands characteristic of tectonically stable coastlines may increase efficiency of carbon sequestration with the onset of accelerated sea-level rise, providing long-term mitigating feedbacks relevant to global climate-carbon modelling