Carbon accumulation rates in salt marsh sediments suggest high carbon storage capacity

Abstract. Studies on carbon stock in salt marsh sediments are increasing. However, uncertainties exist in estimating global carbon storage in these vulnerable coastal habitats, thus hindering the assessment of their importance. Combining direct data and indirect estimation, this study compiled studies involving 158 sites across the southern and Northern Hemispheres, and estimated the global average carbon accumulation rate (CAR) at 242.2 g C m−2 yr−1 in saltmarsh sediments. Based on region-specific CAR and estimates of salt marsh area in various geographic regions between 40° S to 78.3° N, total CAR in global salt marsh sediments is ~ 10.1 Tg C yr−1. 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, there may be uncertainties for our global estimate owing to limited and patchy data availability. CAR of salt marsh sediments changes with latitude, tidal range, halophyte genera and elevation, with considerable variation among different biogeographic regions.