Sources, transport, age, and evolution of terrestrial organic carbon across the Chukchi Sea margin, Arctic Ocean

Global warming and permafrost thawing are expected to release substantial amounts of organic carbon (OC) into the Arctic Ocean, potentially intensifying climate warming through a positive feedback loop. In our study, we investigated the sources, transport, and evolution of terrestrial OC (terr-OC) across the Chukchi Sea margin in the Arctic Ocean, using carbon isotope (¹³C and ¹⁴C) and biomarker (n-alkanes and lignin) analyses. Our findings revealed that terr-OC from various sources, such as Ice Complex Deposits (ICD), topsoil, and high plants, was stored and evolved across the Chukchi continental marginal seas. A dual‑carbon-isotope mixing model indicated that ICD was the dominant terr-OC source (47 ± 21 %) in sediments, with its contribution increasing from the Chukchi shelf to the slope. While, the proportion of topsoil-OC (18 ± 7 %) decreased with distance and over time along the Chukchi slope. The enriched Δ¹⁴C values and higher molecular degradation proxies on the Chukchi shelf suggested that a large proportion of the exogenous terr-OC had undergone significant degradation before reaching the sediment-water interface. During transport, selective degradation occurred, with lignin and n-alkanes declining faster than TOC, and topsoil-OC degrading rapidly than ICD-OC. This prolonged transport likely intensified selective degradation, as changes in terr-OC across the Chukchi shelf to slope were more noticeable than in vertical sediment core profiles. This study emphasizes the Arctic Ocean as a critical sink for diverse forms of terr-OC and highlights the importance of lateral transport, deposition, and degradation in OC burial processes. Further research on precise temporal scales is needed to clarify whether the observed spatial differences stem from variations in sediment sources or from the combined effects of hydrodynamic sorting and selective degradation during lateral transport.