Inefficient burial of terrestrial organic carbon in deltas

• Published in: Earth and planetary science letters Vol. 642; p. 118865
• Main Authors: Yu, Yonggui, Nienhuis, Jaap H., Yao, Zhengquan, van der Perk, Marcel, Zhao, Bin, Qiao, Shuqing, Shi, Xuefa, Cardenas-Belleza, Gabriel, Fu, Sheng, Peterse, Francien, Bai, Yazhi, Middelkoop, Hans
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.09.2024
• Subjects: Organic carbon burial efficiency; Organic carbon isotopes (13C and 14C); Sediment dynamics; Yellow River Delta; Organic carbon burial efficiency; Sediment dynamics; Yellow River Delta; Organic carbon isotopes (13C and 14C)
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2024.118865

•We used a novel bathymetry-based method to date the highly dynamic delta deposits.•The net burial efficiencies of terrestrial organic carbon in age-labeled sediments are ∼50 % lower than previous estimate of proto burial efficiency.•Sediment pathways exert significant controls on the preservation of terrestrial organic carbon. The world's deltas are estimated to store ∼58±17 Tg of terrestrial organic carbon (OCterr) annually, indicating their significant role in the global carbon cycle. However, these estimates are based on the proto burial efficiency (PBE) of OCterr in surface sediments of subaqueous deltas, which assumes that OCterr burial is spatially and temporally homogenous. Yet, the time-dependent OCterr burial and degradation in subaqueous delta deposit is poorly constrained due to the difficulty in determining the chronology of the deposits. By using a novel bathymetry-based method to date core sediments from the subaqueous Yellow River Delta (hereafter YRD), we show that the OCterr burial efficiencies in age-labeled deltaic sediments are highly heterogenous due to different sediment pathways and time-dependent OCterr degradation. River floods lead to an initial OCterr burial efficiency of up to ∼62 %±18 % and negligible marine-derived OC in the flood deposits at the delta front. Subsequent sediment remobilization and early diagenesis, however, lead to substantial attachment of marine OC and degradation of OCterr, eventually resulting in different OC compositions and lower burial efficiencies ranging from 36 %±12 % to 57 %±10 %. Despite the refractory nature of OCterr, the post-burial OCterr degradation rate constant is estimated to be 0.7 per year, further lowering the initial OCterr burial efficiency to ∼36 % after 56 years. Our multi-decadal net OCterr burial efficiency is at least 50 % lower than previous PBE-derived estimates from the YRD. This pattern likely extends to deltas globally, calling for a re-assessment of river delta influence in the global carbon cycle.