CO₂ and CH₄ in sea ice from a subarctic fjord

Abstract

Abstract. We present CH4 concentration [CH4] and the partial pressure of CO2 (pCO2) in bulk sea ice from subarctic, land-fast sea ice in the Kapisillit fjord, Greenland. The bulk ice [CH4] ranged from 1.8 to 12.1 nmol L−1, which corresponds to a partial pressure range of 3 to 28 ppmv. This is markedly higher than the average atmospheric methane content of 1.9 ppmv. Most of the trapped methane within the sea ice was evidently contained inside bubbles, and only a minor portion was dissolved in the brine. The bulk ice pCO2 ranged from 60 to 330 ppmv showing that sea ice at temperatures above −4 °C is under-saturated compared to the atmosphere (390 ppmv). Our study adds to the few existing studies of CH4 and CO2 in sea ice and concludes that sub-arctic sea can be a sink for atmospheric CO2, while being a net source of CH4. Processes related to the freezing and melting of sea ice represents large unknowns to the exchange of CO2 but also CH4. It is therefore imperative to assess the consequences of these unknowns through further field campaigns and targeted research under other sea ice conditions at both hemispheres.