Enhanced terrestrial carbon preservation promoted by reactive iron in deltaic sediments

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 similar to 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 C-13 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 C-13 values. However, only the adsorbed OC displayed preferential binding of lignin phenols. We estimate that similar to 8% of the OC initially deposited in deltaic systems is bound to Fe-R (equivalent to 6x10(12)gCyr(-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.