Carbon sequestration and storage in Norwegian Arctic coastal wetlands: Impacts of climate change

Coastal wetlands contain some of the largest stores of pedologic and biotic carbon pools, and climate change is likely to influence the ability of these ecosystems to sequester carbon. Recent studies have attempted to provide data on carbon sequestration in both temperate and tropical coastal wetlands. Alteration of Arctic wetland carbon sequestration rates is also likely where coastal forcing mechanisms interact directly with these coastal systems. At present there are no data available to provide a detailed understanding of present day and historical carbon sequestration rates within Arctic coastal wetlands. In order to address this knowledge gap, rates of carbon sequestration were assessed within five Arctic coastal wetland sites in Norway. This was undertaken using radiometric dating techniques (²¹⁰Pb and ¹³⁷Cs) to establish a geochronology for recent wetland development, and soil carbon stocks were estimated from cores. Average carbon sequestration rates were varied, both between sites and over time, ranging between 19 and 603 g C m² y^-1, and these were correlated with increases in the length of the growing season. Stocks ranged between 3.67 and 13.79 Mg C ha^-1, which is very low compared with global average estimations for similar coastal systems, e.g. 250 Mg C ha^-1 for temperate salt marshes, 280 Mg C ha^-1 for mangroves, and 140 Mg C ha^-1 for seagrasses. This is most likely due to isostatic uplift and sediment accretion historically outpacing sea level rise, which results in wetland progradation and thus a continuous formation of new marsh with thin organic soil horizons. However, with increasing rates of sea level rise it is uncertain whether this trend is set to continue or be reversed.