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

The balance between remineralization and sedimentary burial of terrestrial organic carbon (OC_terr) in large river-dominated marginal seas influences atmospheric CO₂ inventory on a range of timescales. Here we systematically investigate the evolution of OC_terr along the river-estuary-coastal ocean continuum for 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. Lower plant-wax fatty acid ¹⁴C contents suggest selective degradation of labile OC within estuaries, resulting in apparent aging of OC_terr, followed by an apparent rejuvenation in OC_terr in shelf sediments, the latter likely reflecting inputs from proximal sources that contribute younger OC_terr. This selective degradation, aging and rejuvenation of OC_terr along the 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.