Precisely dated records of pre-aged terrestrial organic matter release to the western Laptev Sea during the last deglaciation

Abstract. Rapid mobilization of organic carbon from thawing terrestrial permafrost into the Arctic Ocean has been documented for several intervals during the last deglaciation based on marine sediment archives. Assessing the significance of this process for the global carbon cycle requires robust chronological control to better constrain the potential environmental drivers of terrestrial organic carbon mobilization. Identifying the sources of the mobilized terrigenous material is equally critical, as terrestrial permafrost deposits of different ages vary in their potential to release greenhouse gases upon thawing. Motivated by these needs, this study derived a precise age model for a sediment record composed of two cores retrieved from the western Laptev Sea (PS51/154-11 and PS51/159-10) and investigated whether the sources of mobilized permafrost materials during periods of rapid terrestrial permafrost thaw varied over time. This was achieved by aligning ¹⁰Be/⁹Be variations between marine sediment and ice core records, revealing that the age difference between local and global marine reservoir ages (ΔR) was -164 ± 56 ¹⁴C yr on the western Laptev Sea shelf and remained relatively stable from the last deglaciation to the present. The previously published radiocarbon-based age-depth models for the two cores were refined using this updated ΔR value, enabling a precise temporal assessment of these records. Radiocarbon ages of terrestrial biomarkers were determined from intervals of maximal terrestrial organic matter delivery recorded in cores PS51/154-11 and PS51/159-10. Compound-specific ¹⁴C ages of high molecular weight (n-C_28:0) fatty acids indicated source variations influenced by transport mechanisms, with a higher contribution of aged material during periods of rapid coastal-eroded terrestrial permafrost mobilization and a dominance of near-surface, younger permafrost during intervals of elevated river discharge. In contrast, mid-chain (n-C₂₃+n-C₂₅) and high molecular weight (n-C₂₉+n-C₃₁) n-alkanes suggested ancient permafrost to be the predominant source for terrestrial inputs to the marine shelf during periods of accelerated land-to-ocean exchange. Our findings on the pre-depositional ¹⁴C ages of terrestrial biomarkers highlighted the complexity of permafrost mobilization pathways as captured by different lipid compounds.