Characteristics of sedimentary organic carbon burial in the shallow conduit portion of source-to-sink sedimentary systems in marginal seas.

Multistep physical and biological processing of organic matter in marginal seas modifies its composition, sedimentary pathway, and burial efficiency. This study examines how organic geochemical signals pertaining to the source and transformation in surface sediments are transported and preserved in the conduit portion of source-to-sink sedimentary systems in marginal seas such as the Taiwan Strait (TS). The aim is to gain more insight in not only the total OC burial in this highly dynamic region, but also to establish a quantitative assessment of the provenance and age of this carbon. Our study revealed that terrestrial plant wax n -alkanols represent a portion of terrestrial organic matter, characterized by refractory property and strong mobility leading to efficient transfer from the river mouth to the shelf. Soil bacteria-derived branched glycerol dialkyl glycerol tetraethers (br-GDGTs) represent the portion of terrestrial OM characterized by labile properties and low transmissibility restricted within the river mouth under normal conditions, except for episodic and pulse delivery situations. Sedimentary OC in the TS is typically characterized by a large amount of ancient OC with intensive oxidation, indicated by extremely old 14C ages (<13000 ± 180 yr) and lower petrogenic OC content in marine sediments than that of rocks sourced from the land. Diverse sourced OC supply and accumulation patterns in shallow marine conduit systems mainly influenced by complex physical processes. Quantitative source apportionment of sedimentary OC using a ternary mixing model based on the bulk δ13C and Δ14C proxies combined with sediment mass accumulation rates revealed 0.01–3.44, 0.002–3.79, and 0–3.38 mg C cm−2 yr−1 of marine, terrestrial biospheric, and petrogenic OC burial loadings in the TS. Marine OC burial could only explain 30% of net air–sea CO 2 sequestration in a narrow conduit system such as the TS, which is characterized by high sediment resuspension and strong hydrodynamic processes due to strong tidal currents and wind-driven circulation. Our findings revealed the net C buried in different marginal seas varies as a function of local couplings between physical processes and biogeochemical characteristics. [ABSTRACT FROM AUTHOR]