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 CH 4 and N 2 O fluxes across a glacier‐lagoon‐ocean continuum in Iceland. Surface water CH 4 ranged from 690% supersaturation relative to atmospheric equilibrium near the glacier to 140% on the shelf. N 2 O was undersaturated (84 ± 21%) near the glacier front and approached equilibrium in coastal seawater. The glacial lagoon was a CH 4 source to the atmosphere and N 2 O sink, while nearshore shelf waters were a weak source of both gases. The total shelf CH 4 emissions to the atmosphere were one order of magnitude greater than the lateral freshwater dissolved CH 4 exports from the lagoon. The strong regional marine CO 2 sink exceeds the CO 2‐ equivalent global warming potentials of CH 4 and N 2 O emissions to the atmosphere by one order of magnitude. Overall, the glacier‐lagoon‐shelf continuum remains a major carbon sink despite widespread CH 4 emissions and variable N 2 O sink/source behavior.