"Among the mechanisms that could move significant quantities of green house gases into the atmosphere within this century, climate scientists are particularly concerned about the carbon (C) locked in permanently frozen Arctic ground that is now being released because of warming temperatures. Given the extent of this mega-pool of C (~1,400 Gt of C) susceptible to climate-induce changes compared to the atmospheric reservoir (~750 Gt of C), the potential release of this stock into the atmosphere due to thawing is considered a serious risk for the future climate. Recent studies suggest that a significant fraction of previously frozen soil will be re-located along the Arctic shelf. Indeed there are ample of evidence indicating that land-to-ocean fluxes of organic carbon (OC) along the Arctic coasts are changing because of thermal collapse of coastal permafrost and increase of the river runoff. However, the fate of this material once re-introduced in the marine carbon cycle is poorly constrained.With this project we propose to address this critical knowledge gap by analyzing the composition and physical properties of surface sediments from the Siberian Shelf. Our overarching objective is to develop and test a sensitive proxy of land-derived OC degradation in a system that will experience a massive supply of terrigenous material in the near future. The extent of degradation will be assessed using mineral surface-normalized concentrations of terrigenous OC. This latter will be characterized at molecular level using a suite of terrigenous biomarkers including lignin phenols, cutin-derived products, and high molecular weight compounds (n-alkanols, n-alkanoic acids and n-alkanes). The degree of soil-OC degradation will be assesses as a function of the depletion of the terrigenous biomarkers loadings relative to the original concentrations in river and permafrost samples. The study will be carried out on different sediment size fractions to avoid sorting bias."