Controls on Organic Carbon Burial in the Eastern China Marginal Seas: A Regional Synthesis

• Published in: Global biogeochemical cycles Vol. 35; no. 4
• Main Authors: Zhao, B., Yao, P., Bianchi, T. S., Yu, Z. G.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-04-2021
• Subjects: Accumulation; Anthropogenic factors; Brackishwater environment; Burial efficiency; Carbon; Carbon budget; Carbon dioxide; Carbon dioxide atmospheric concentrations; Coastal plains; Dam construction; Decay; Dispersal; Dispersion; Drainage basins; Drawdown; Eastern China Marginal Seas; Estuaries; Fluvial sediments; Isotope composition; Marginal seas; Mud; mud areas; Oceans; Organic carbon; Oxidoreductions; Particulate matter; Redox properties; Residence time; River basins; River sediments; Rivers; Sediment; Sediment load; Sediment mixing; sedimentary regime; Sediments; Silicates; Suspended particulate matter; Synthesis; Terrestrial environments; Weathering; China; Yellow River
• ISSN: 0886-6236; 1944-9224
• DOI: 10.1029/2020GB006608

A regional synthesis of organic carbon (OC) burial was conducted using a comprehensive data set to reveal some of the key drivers and human multi‐stressors controlling OC burial and transport in the Eastern China Marginal Seas (ECMS). Both OC and Δ14C values of suspended particulate matter (SPM) in the Changjiang River, were significantly higher than estuarine mobile‐muds, suggesting selective decay of more labile younger OC from both marine and terrestrial sources and the accumulation of more recalcitrant older OC. Some of this decay is likely to be associated with iron‐redox cycling in mobile‐muds. In contrast, OC, δ13C, and Δ14C values increased along the Yellow River sediment dispersal pathway, indicating adding of young marine OC and less decay of terrestrial OC. OC burial efficiency in mud areas in the Bohai Sea (∼43%) was significantly higher than those in the Yellow (∼11%) and East China Seas (∼16%), owing to rapid deposition. Burial flux of biospheric OC in mud areas of the ECMS is 7.00 ± 0.79 Mt yr−1, corresponding to atmospheric CO2 drawdown by silicate weathering in major river drainage basins of mainland China. The burial flux of petrogenic OC was estimated to be 0.81 ± 0.25 Mt yr−1, accounting for >1.9% of total burial in the global ocean. While the ECMS is an important OC sink, river damming has greatly reduced OC burial. Thus, the overall impact on anthropogenically altered river‐dominated marginal seas remains an important and rapidly changing component of the coastal ocean carbon budget.
Plain Language Summary
A comprehensive regional synthesis of organic carbon (OC) burial and its drivers, were investigated across the Eastern China Marginal Seas (ECMS). Variation of OC content and carbon isotopic composition from suspended particulate matter to mobile muds, in Changjiang sediment dispersal pathways, indicated selective decomposition of younger more labile marine and terrestrial OC, which resulted in the accumulation of older more recalcitrant OC. However, continuous adding of young marine OC, with little loss of terrestrial OC, in Yellow River sediment dispersal pathway, resulted in more recalcitrant terrestrial OC buried in this relatively more quiescent sedimentary regime. Burial efficiencies of OC from different sources in the ECMS were mainly controlled by OC reactivity and sediment mixing dynamics. The ECMS is an important sink of both petrogenic and biospheric OC over a timescale of ∼100 years. However, dam building in river basins has reduced sediment loads of the Changjiang and Yellow Rivers, which will continually decrease OC burial in the ECMS for decades to come. The changing residence time and redox pathways in these sedimentary regimes, partly controlled by increasing human stressors in the ECMS, are expected to have an important impact on rates of OC turnover and burial in marginal seas.
Key Points
Aging of terrestrial organic carbon in the Changjiang sedimentary system is more intense than that in the Yellow River sedimentary system
More efficient burial of organic carbon in the quiescent Bohai and Yellow Seas mud areas compared to East China Sea mobile muds
The Eastern China Marginal Seas are important OC sinks in terms of both petrogenic and biospheric OC burial fluxes