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, Δ14COC‑Fe values fall within the range of from −358.73
to −64.03‰, and both Δ14COC‑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.