Extraction Strategies for Profiling the Molecular Composition of Particulate Organic Matter on Glacier Surfaces

Pigmented microalgae thrive on supraglacial surfaces, producing "sticky" extracellular polymeric substances that combine into a mineral-organic matrix. Together, they enhance snow and ice melting by lowering the albedo. Understanding the chemical nature of particulate organic matter (POM) in this matrix is crucial in assessing its role in supraglacial carbon dynamics. We evaluated POM complexity in alga-rich snow and ice samples containing 0.3-6.4 wt % organic carbon (OC) via extractions with solvents of varying polarity, pH, and OM selectivity. Extraction yields were evaluated by OC analysis of the extracts, and the composition of extracted OM was analyzed using ultrahigh-resolution mass spectrometry. Individual hot water (HW), hydrochloric acid (HCl), and sodium hydroxide (NaOH) extractions achieved up to 87% efficiency, outperforming sequential, organic solvent-based extractions (<11%). OM extracted by HW, HCl, and NaOH combined had more molecular formulas (2827) than OM extracted with organic solvents (1926 formulas). Combined HW, NaOH, and HCl extractions yielded an OM composition with unsaturated, highly unsaturated, aromatic, and N-containing compounds, while unsaturated aliphatics and black carbon-derived polycyclic aromatics were enriched in the organic solvent extracts. This molecular profiling provides the first comprehensive insights into supraglacial POM composition, opening the window for understanding its role in the cryospheric carbon cycle.