Source to Sea: The Climate Mitigation Significance of Shelf Sea Sedimentary Organic Carbon Stores

The burial of organic carbon (OC) in coastal and continental shelf sediments contributes to the regulation of atmospheric carbon dioxide on geological timescales and potentially mitigates present-day climate change. Major efforts are now underway to map and quantify the OC held in our continental shelf seas, including the first ever assessment of a national Exclusive Economic Zone (EEZ) sediment OC resource for the United Kingdom. When these OC-rich sediments are disturbed, either by natural or (increasingly) anthropogenic pressures, there is potential for significant quantities of carbon dioxide to be released to the water column and potentially the atmosphere. The reactivity of sedimentary OC is generally defined as a susceptibility to decomposition, biotically or abiotically. Reactivity of OC in marine sediments determines the role the store plays in climate regulation and, equally, determines the vulnerability of the sedimentary OC store to disturbance both natural and anthropogenic. The recent development of the Carbon Reactivity Index (CRI) as a novel measure of OC reactivity based on thermogravimetric analysis has highlighted a wide continuum of OC reactivity in sediments across continental shelf seas. Here, we present new results that highlight the continuity of these processes across the land-ocean transition in the major estuaries (Clyde and Forth) of Scotland. Our results highlight new opportunities to integrate the protection of vulnerable sediment OC stores into objective marine management plans across coastal and shelf seas.