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 (OCterr) in large river-dominated marginal seas influences atmospheric CO2 inventory on a range of timescales. Here we systematically investigate the evolution of OCterr 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 OCterr. Lower plant-wax fatty acid 14C contents suggest selective degradation of labile OC within estuaries, resulting in apparent aging of OCterr, followed by an apparent rejuvenation in OCterr in shelf sediments, the latter likely reflecting inputs from proximal sources that contribute younger OCterr. This selective degradation, aging and rejuvenation of OCterr along the continuum confounds the use of plant wax lipid 14C to constrain lateral transport times, and sheds light on more complex OCterr dynamics in marginal seas.