468 / 2024-09-17 18:11:02

Preservation of Organic Carbon Associated with Iron on Continental Shelves Influenced by Hydrodynamic Processes

organic carbon, marine sediments, iron, carbon cycle, hydrodynamic processes

Understanding the environmental fate of organic carbon associated with iron (OC-Fe) is critically important for investigating OC preservation in aquatic systems. Here, we first investigate ¹³C and ¹⁴C isotopes of OC-Fe within grain size-fractionated sediments retrieved from the East China Sea and estimate their sources and reactivities of OC-Fe through isotope-mixing models and thermal pyrolysis approaches in order to reveal the fate of OC-Fe on continental shelves influenced by hydrodynamic processes. Our results show that the OC-Fe proportion in total OC ( f _OC‑Fe)in the sortable silt fractions (20−63 μm) is the highest among three grain size fractions, likely suggesting that hydrodynamics may enhance the iron protection on OC. In addition, Δ¹⁴C_OC‑Fe values fall within the range of from −358.73 to −64.03 ‰, and both Δ¹⁴C_OC‑Fe values and ancient OC-Fe% exhibit strong positive linear relationships with f _OC‑Fe. This emphasized that the hydrodynamic processes may cause the ancient OC to be tightly associated with Fe, accompanying OC-Fe aging. Our findings shed new light on the preservation of OC-Fe in marginal seas to advance the recognition of carbon “rusty sinks” in seafloor sediments.