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 CO2-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.