Abstract
Preservation of organic carbon (OC) in marine and terrestrial deposits
is enhanced by bonding with reactive iron (FeR) phases. The association
of OC with FeR (OC-FeR) provides physical protection and hinders
microbiological degradation. Roughly 20% of all OC stored in
unconsolidated marine sediments and 40% of all OC present in Quaternary
terrestrial deposits is preserved as OC-FeR, but this value varies from
10 to 80% across depositional environments. In this work, we provide a
new assessment of global OC-FeR burial rates in both marine and
terrestrial environments, using published estimates of the fraction of
OC associated with FeR, carbon burial, and probabilistic modelling. We
estimate the marine OC-FeR sink at between 31 – 70 Mt C yr-1 (mean 52
Mt C yr-1), and the terrestrial OC-FeR sink at between 171 - 946 Mt C
yr-1 (mean 472 Mt C yr-1). In marine environments, continental shelves
(mean 17 Mt C yr-1) and deltaic/estuarine environments (mean 11 Mg C
yr-1) are the primary locations of OC-FeR burial. On land, croplands
(279 Mt C yr-1) and grasslands (121 Mt C yr-1) dominate the OC-FeR
burial budget. Changes in the Earth system through geological time
likely alter the OC-FeR pools, particularly in marine locations. For
example, periods of intense explosive volcanism may lead to increased
net OC-FeR burial in marine sediments. Our work highlights the
importance of OC-FeR in marine carbon burial and demonstrates how OC-FeR
burial rates may be an order of magnitude greater in terrestrial
environments, those potentially most sensitive to anthropogenic impacts.