Autogenic shoreline migration and its effect on the storage of carbon in marginal marine successions

The accumulation of organic matter (OM) near shorelines, known as blue carbon, is a key sink in the global carbon cycle. This accumulation is influenced by elevation relative to sea level of the delta-top, which changes through the movement of shorelines with time. The influence of internally generated, or autogenic, delta dynamics on meso-timescale (<105 yr) OM preservation in river deltas is unknown. We develop a framework that links local autogenic shoreline migration to the spatial extent of preserved organic-rich strata, which we term paleo-blue carbon, and validate this against observations from a physical experiment that couples a clastic delta to a coastal wetland environment. We show that autogenic processes exert a control on shoreline migration and preservation of organic material: the longitudinal subsurface extent of paleo-blue carbon is approximately seven times larger than the wetland accumulation zone on the surface at any given period. Further, autogenic processes enhance carbon burial rates, which are fast enough to be preserved prior to degradation. Given that autogenic processes operate in sedimentary environments that accumulate appreciable quantities of OM, we recommend incorporation of this framework into any predictions of the spatial extent of paleo-blue carbon stored in strata.