Biochemical and molecular fingerprinting of soil organic matter fractions reveals diverse sources and stabilization mechanisms in Maritime Antarctica

Understanding the biochemical composition and stabilization mechanisms of soil organic matter (SOM) is essential for assessing its persistence in rapidly changing polar environments. In this study, we investigated the molecular, elemental, and isotopic characteristics of SOM fractions—particulate (POM) and mineral-associated organic matter (MAOM)—in soils from the Byers Peninsula, Maritime Antarctica. Using δ 13 C and δ 15 N isotopic signatures, off-line TMAH thermochemolysis, solid-state 13 C NMR spectroscopy, and thermogravimetric analysis (TGA), we identified key pathways of SOM stabilization and origin. Results revealed that lipid-derived compounds dominated both SOM fractions (39–96%), with lignin detected exclusively in vascular plant residues and only marginally in MAOM. Isotopic signatures indicated multiple organic matter sources, including C 3 plant biomass, marine inputs, ornithogenic deposits, and endolithic communities. Soils affected by cryoturbation and located on high and low platforms exhibited the highest carbon and nitrogen stocks, primarily stabilized in the MAOM fraction. Molecular analyses demonstrated significant variation in SOM composition across soil profiles. While most soils exhibited high proportions of labile O-alkyl C compounds, select profiles (notably P2 and P4) showed enriched aryl C and elevated thermostability, indicating advanced humification and greater molecular complexity. These findings highlight the central role of cryoturbation, hydrophobic interactions, and microbial-derived inputs in stabilizing SOM in the absence of lignin-rich vegetation. Overall, our integrated fingerprinting approach revealed that SOM persistence in Maritime Antarctica is governed by both physical protection (via MAOM) and biochemical resistance, offering critical insights into its potential response to ongoing climate-driven changes. • Byers Peninsula SOM is lipid-rich, dominated by hydrophobic long-chain hydrocarbons. • Isotopic signatures reveal diverse SOM sources reflecting colonization and landscape changes. • Cryoturbation and hydrophobicity stabilize SOM, compensating for the absence of lignin. • Glacier retreat and ecosystem shifts alter SOM formation, stabilization, and native SOM quality.