Geomorphic and ecological constraints on the coastal carbon sink

Climate change is driving a fundamental reorganization of the coastal zone, in which carbon-rich ecosystems are simultaneously migrating, accreting and submerging. In this Review, we discuss the geomorphic processes constraining soil carbon accumulation and the ecological processes constraining greenhouse gas emissions that together determine the net radiative forcing of the coastal landscape and the size of the coastal carbon sink. Sea level rise creates vertical and lateral accommodation space that potentially enhances soil carbon accumulation in marshes and mangroves. However, sea level rise and saltwater intrusion lead to ecosystem transitions that result in loss of existing carbon pools, altering the balance between carbon sequestration and greenhouse gas emissions. We propose that ecosystem reorganization results in large, but mostly offsetting, changes in radiative forcing. At the continental scale, losses in soil carbon sequestration and wood production are offset by reduced methane emissions associated with salinization of freshwater ecosystems. Nevertheless, climate effects on the coastal carbon sink remain largely studied within individual ecosystems. Future work is needed to determine the connectivity of carbon between ecosystems, changes in carbon accumulation and greenhouse gas emissions as ecosystem transitions occur, and the fate of carbon as it moves through the coastal landscape. Geomorphic and ecological factors shape the effects of sea level rise on the coastal carbon sink. This Review discusses how reductions in greenhouse gas emissions compensate for losses in carbon sequestration as ecosystem boundaries change rapidly in the coastal zone.

Automated summary

Climate change is causing significant changes in the coastal zone, with carbon-rich ecosystems undergoing migration, growth, and submergence. This review analyzes the processes influencing soil carbon accumulation and greenhouse gas emissions, which determine the radiative forcing and size of the coastal carbon sink. Sea level rise can enhance soil carbon accumulation, but it also leads to ecosystem transitions and the loss of existing carbon pools. This study emphasizes the need for further research on the connectivity of carbon between ecosystems and the effects of ecosystem transitions on carbon accumulation and emissions in the coastal landscape.