Combined CH4, N2O, and CO2 Fluxes Reveal a Net Carbon Sink Across a Glacier-Ocean Continuum

Abstract

Rapidly retreating marine-terminating glaciers potentially release trapped greenhouse gases to the atmosphere. Here, we quantified water-air CH₄ and N₂O fluxes across a glacier-lagoon-ocean continuum in Iceland. Surface water CH₄ ranged from 690% supersaturation relative to atmospheric equilibrium near the glacier to 140% on the shelf. N₂O was undersaturated (84 ± 21%) near the glacier front and approached equilibrium in coastal seawater. The glacial lagoon was a CH₄ source to the atmosphere and N₂O sink, while nearshore shelf waters were a weak source of both gases. The total shelf CH₄ emissions to the atmosphere were one order of magnitude greater than the lateral freshwater dissolved CH₄ exports from the lagoon. The strong regional marine CO₂ sink exceeds the CO_2-equivalent global warming potentials of CH₄ and N₂O emissions to the atmosphere by one order of magnitude. Overall, the glacier-lagoon-shelf continuum remains a major carbon sink despite widespread CH₄ emissions and variable N₂O sink/source behavior.