Tracing cross-shelf transport and accumulation of particulate organic carbon in the continental margin bottom sediments using Aluminum and 210Pb

Abstract

We investigated particulate organic carbon (POC) transport across the shelf to the basin bottom in the East/Japan Sea, using Aluminum (Al) and ²¹⁰Pb as tracers. Our results show that the sedimentary deposition of ²¹⁰Pb in the basin (2327 m) is comparable with the scavenging removal flux from the water column (117 ± 15 %), whereas it increases threefold in the shelf (296 ± 50 %) (200 m), suggesting substantial lateral inputs of land- and shelf-origin sediments. We also show that conventionally used excess ²¹⁰Pb-derived sedimentation rates without considering mixing can be overestimated by 3–8 times in continental margin sediments, where sedimentation rates are low (< 0.15 cm yr⁻¹), leading to significant overestimation of POC burial fluxes. Sedimentation rates based on an Al mass balance with sedimentary ²¹⁰Pb budgets align more closely with those from ¹⁴C and tephra analyses in this region. A POC box model using the refined sedimentation rate indicates that POC burial fluxes in the East Sea are 0.3–1.0 % of primary production. These values are four times lower than previous estimates based on ²¹⁰Pb-derived sedimentation rates in the same region, but consistent with those observed in similar oceanic settings. Additionally, the POC box model suggests that sediment resuspensions can significantly contribute (34–70 %) to sinking POC fluxes in the bottom sediments. Thus, our results highlight that in continental margins, where ²¹⁰Pb decay and mixing are difficult to distinguish due to slow sedimentation rates, traditional ²¹⁰Pb dating methods can significantly overestimate sedimentation rates and associated material fluxes.