Preservation of organic carbon (OC) in marine and terrestrial deposits is enhanced by bonding with reactive iron (FeR). 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 global depositional environments. Here, we provide a new assessment of global OC-FeR burial rates in both marine and terrestrial environments, using published estimates of OC associated with FeR, carbon burial, and probabilistic modeling. We estimate the marine OC-FeR sink between 31 and 70 Mt C yr−1 (average 52 Mt C yr−1), and the terrestrial OC-FeR sink at between 146 and 917 Mt C yr−1 (average 446 Mt C yr−1). In marine environments, continental shelves (average 17 Mt C yr−1) and deltaic/estuarine environments (average 11 Mg C yr−1) are the primary settings 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 impact the OC-FeR pools, particularly in marine settings. 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, but here OC-FeR stocks are most sensitive to the anthropogenic impacts of climatic change.
|Number of pages||18|
|Journal||Global Biogeochemical Cycles|
|Early online date||23 Nov 2022|
|Publication status||Published - Nov 2022|