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.