Apparent Aging and Rejuvenation of Terrestrial Organic Carbon Along the River‐Estuary‐Coastal Ocean Continuum

Abstract

The fates of terrestrial organic carbon (OC_terr) during fluvial transport from land to ocean are still not well constrained. This study systematically examines the evolution and dynamics of OC_terr along the river‐estuary‐coastal ocean continuum in three fluvial systems discharging to the Chinese marginal seas. The ¹⁴C‐depleted characteristics of bulk OC and molecular components of riverine suspended sediments and marine sediments suggest that the Chinese marginal seas are a significant sink of pre‐aged OC_terr. Our study reveals significant apparent aging of OC_terr within estuaries, likely due to degradation of (younger) labile components, and apparent rejuvenation of OC_terr in shelf systems, likely reflecting inputs of younger OC_terr from proximal sources along the sediment dispersal pathway. The aging and rejuvenation of OC_terr along the river‐ocean continuum confounds the use of plant wax lipid ¹⁴C to constrain lateral transport times, and sheds light on more complex OC_terr dynamics in marginal seas.