Sea-level rise enhances carbon accumulation in United States tidal wetlands

Coastal wetlands accumulate soil carbon more efficiently than terrestrial systems, but sea level rise potentially threatens the persistence of this prominent carbon sink. Here, we combine a published dataset of 372 soil carbon accumulation rates from across the United States with new analysis of 131 sites in coastal Louisiana and find that the rate of relative sea level rise (RSLR) explains 80% of regional variation in carbon accumulation. A carbon mass balance for the rapidly submerging Louisiana coast demonstrates that carbon accumulation rates in surviving marshes increase with RSLR and currently exceed the rate of carbon loss due to marsh drowning and erosion. Although continued erosion will eventually lead to net carbon loss, together these results suggest a strong negative carbon-climate feedback for coastal marshes, where even submerging marshes sequester carbon at rates that increase with RSLR.