Enhanced terrestrial carbon preservation promoted by reactive iron in deltaic sediments

Abstract We examined the role of reactive iron (Fe R ) in preserving organic carbon (OC) across a subaerial chronosequence of the Wax Lake Delta, a prograding delta within the Mississippi River Delta complex. We found that ~15.0% of the OC was bound to Fe R , and the dominant binding mechanisms varied from adsorption in the youngest subaerial region to coprecipitation at the older, vegetated sites. The δ 13 C of the iron‐associated OC was more negative than the total OC (mean = −2.6‰), indicating greater preference for terrestrial material and/or compounds with more negative δ 13 C values. However, only the adsorbed OC displayed preferential binding of lignin phenols. We estimate that ~8% of the OC initially deposited in deltaic systems is bound to Fe R (equivalent to 6 × 10 12 gC yr −1 ), and this percentage increases postdepositionally, as coprecipitation of Fe R and OC allows for an even greater amount of OC to be bound to Fe R .