Key role of river deltas in carbon sequestration through biospheric organic carbon burial

Abstract Biospheric organic carbon (OC) burial and petrogenic OC oxidation are fundamental controls in the regulation of global CO2 concentrations. River deltas are among the largest OC sinks in the ocean, storing substantial amounts of terrestrial OC originating from both the biosphere and lithosphere. However, the extent of biospheric and petrogenic OC storage in deltas remains poorly understood. Here, we quantified biospheric and petrogenic OC burial rates in a dynamic river delta, the Yellow River Delta, using geomorphology and carbon isotopic analyses. The Yellow River Delta is characterized by high burial rates of petrogenic OC (109 ± 27 g m–2 yr–1) and pre-aged soil OC (107 ± 27 g m–2 yr–1), followed by terrestrial modern OC (87 ± 21 g m–2 yr–1) and marine OC (48 ± 16 g m–2 yr–1). The deltaic biospheric OC burial rate (242 g m–2 yr–1) is up to 70 times higher than the global average in marginal seas. By analyzing biospheric and petrogenic OC burial rates and fluxes in global deltas and marginal seas, we highlight the critical role of deltas as major sinks for biospheric OC. This study underscores the importance of distinguishing between biospheric and petrogenic OC when assessing carbon sinks to better constrain their influence on atmospheric CO2 levels.