Abstract
Abstract. We present the CH4 concentration [CH4], the partial pressure of CO2 (pCO2) and the total gas content in bulk sea ice from subarctic, land-fast sea ice in the Kapisillit fjord, Greenland. Fjord systems are characterized by freshwater runoff and riverine input and based on δ18O data, we show that > 30% of the surface water originated from periodic river input during ice growth. This resulted in fresher sea-ice layers with higher gas content than is typical from marine sea ice. The bulk ice [CH4] ranged from 1.8 to 12.1 nmol L−1, which corresponds to a partial pressure ranging from 3 to 28 ppmv. This is markedly higher than the average atmospheric methane content of 1.9 ppmv. Evidently most of the trapped methane within the ice was contained inside bubbles, and only a minor portion was dissolved in the brines. The bulk ice pCO2 ranged from 60 to 330 ppmv indicating that sea ice at temperatures above −4 °C is undersaturated compared to the atmosphere (390 ppmv). This study adds to the few existing studies of CH4 and CO2 in sea ice, and we conclude that subarctic seawater can be a sink for atmospheric CO2, while being a net source of CH4.
Highlights
The main driver of climate warming is the accumulation of greenhouse gases such as CO2, CH4 and N2O within the atmosphere
Except for a thin layer of granular ice at the top of the ice, the ice exclusively consisted of columnar ice indicating that ice growth occurred through quiet congelation of seawater at the ice–water interface (Eicken, 2003)
The bulk ice temperature ranged from −3.7 to −0.8 ◦C with the lowest values in the upper layers (Fig. 2a)
Summary
The main driver of climate warming is the accumulation of greenhouse gases such as CO2, CH4 and N2O within the atmosphere. CO2 is the most important in terms of radiative forcing, followed by methane (Ramaswamy et al, 2001). The concentrations of these gases in the atmosphere are 390 and 1.9 ppmv, respectively (2013 levels – http://www.esrl.noaa.gov/gmd/aggi/). Sea ice was long considered as an inert barrier for gas exchange between the atmosphere and the ocean (Tison et al, 2002), but there is growing evidence to suggest that sea ice might significantly contribute to the fluxes of climatically active biogases (CO2, CH4) between the ocean and the atmosphere (Delille et al, 2007; Geilfus et al, 2012a, 2013a; Nomura et al, 2010, 2013; Semiletov et al, 2004; Zemmelink et al, 2006). Damm et al (2005, 2007, 2010) and Kort et Published by Copernicus Publications on behalf of the European Geosciences Union
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