Organic Carbon Burial With Reactive Iron Across Global Environments

Abstract Preservation of organic carbon (OC) in marine and terrestrial deposits is enhanced by bonding with reactive iron (Fe R ). Association of OC with Fe R (OC‐Fe R ) 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‐Fe R , but this value varies from 10% to 80% across global depositional environments. Here, we provide a new assessment of global OC‐Fe R burial rates in both marine and terrestrial environments, using published estimates of OC associated with Fe R , carbon burial, and probabilistic modeling. We estimate the marine OC‐Fe R sink between 31 and 70 Mt C yr −1 (average 52 Mt C yr −1 ), and the terrestrial OC‐Fe R 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‐Fe R burial. On land, croplands (279 Mt C yr −1 ) and grasslands (121 Mt C yr −1 ) dominate the OC‐Fe R burial budget. Changes in the Earth system through geological time impact the OC‐Fe R pools, particularly in marine settings. For example, periods of intense explosive volcanism may lead to increased net OC‐Fe R burial in marine sediments. Our work highlights the importance of OC‐Fe R in marine carbon burial and demonstrates how OC‐Fe R burial rates may be an order of magnitude greater in terrestrial environments, but here OC‐Fe R stocks are most sensitive to the anthropogenic impacts of climatic change.