Updated estimates of carbon accumulation rates in coastal marsh sediments

Studies on carbon stock in salt marsh sediments have increased since the review by Chmura et al. (2003). However, uncertainties exist in estimating global carbon stor- age in these vulnerable coastal habitats, thus hindering the as- sessment of their importance. Combining direct data and in- direct estimation, this study compiled studies involving 143 sites across the Southern and Northern hemispheres, and pro- vides an updated estimate of the global average carbon ac- cumulation rate (CAR) at 244.7 g C m 2 yr 1 in salt marsh sediments. Based on region-specific CAR and estimates of salt marsh area in various geographic regions between 40 S to 69.7 N, total CAR in global salt marsh sediments is esti- mated at 10.2 Tg C yr 1 . Latitude, tidal range and elevation appear to be important drivers for CAR of salt marsh sedi- ments, with considerable variation among different biogeo- graphic regions. The data indicate that while the capacity for carbon sequestration by salt marsh sediments ranked the first amongst coastal wetland and forested terrestrial ecosystems, their carbon budget was the smallest due to their limited and declining global areal extent. However, some uncertainties remain for our global estimate owing to limited data avail- ability.