Coastal wetland response to sea level rise in Connecticut and New York

•Marsh accretion accelerated during the 20thcentury in response to sea level rise.•Marsh blue carbon storage increased along with accretion.•Despite increased accretion, marshes lost ground to sea level rise and became wetter over time.•Spartina patens areas submerged more than areas of short Spartina alterniflora.

The persistence of salt marshes in the landscape depends on their ability to accommodate rising sea level and minimize additional flooding stress. We use sediment cores and water level data from 14 marshes in Connecticut and New York to evaluate how marsh accretion, mineral and organic accumulation, carbon storage, and hydroperiod have changed from 1900 to 2012. We observe a regional acceleration in marsh accretion beginning around 1940, although marsh accretion did not reach parity with sea level rise for several additional decades. Despite a rise in marsh accretion from 1.0 mm yr−1 circa 1900 to 3.6 mm yr−1 at present, the marsh surface has lost elevation relative to tidal datums. Declining relative elevations have led to increased tidal flooding, particularly in high marsh settings. As flooding increased, organic matter accumulation accelerated at all marshes. Accelerating mineral deposition was only observed in areas of short-form Spartina alterniflora. Mineral and organic sediment accumulation co-limit accretion, but organic accumulation was the stronger limiting factor, suggesting that marsh response to sea level rise in the region is sensitive to processes affecting rates of belowground production and decomposition. Marsh carbon storage over the period of study averaged 84 g C m−2 yr−1, increasing as accretion accelerated. If marshes remain spatially intact as sea levels rise, these results suggest that marshes have the capacity to become even greater C sinks.