Abstract
Abstract. Rare CO2 flux measurements from Arctic pack ice show that two types of ice contribute to the release of CO2 from the ice to the atmosphere during winter and spring: young, thin ice with a thin layer of snow and older (several weeks), thicker ice with thick snow cover. Young, thin sea ice is characterized by high salinity and high porosity, and snow-covered thick ice remains relatively warm ( > −7.5 °C) due to the insulating snow cover despite air temperatures as low as −40 °C. Therefore, brine volume fractions of these two ice types are high enough to provide favorable conditions for gas exchange between sea ice and the atmosphere even in mid-winter. Although the potential CO2 flux from sea ice decreased due to the presence of the snow, the snow surface is still a CO2 source to the atmosphere for low snow density and thin snow conditions. We found that young sea ice that is formed in leads without snow cover produces CO2 fluxes an order of magnitude higher than those in snow-covered older ice (+1.0 ± 0.6 mmol C m−2 day−1 for young ice and +0.2 ± 0.2 mmol C m−2 day−1 for older ice).
Highlights
Arctic sea ice is changing dramatically, with rapid declines in summer sea ice extent and a shift towards younger and thinner first-year ice rather than thick multi-year ice (e.g., Stroeve et al, 2012; Meier et al, 2014; Lindsay and Schweiger, 2015)
The sea ice CO2 fluxes depend on (a) the difference in the partial pressure of CO2 between the sea ice surface and air, (b) brine volume fraction at the ice–snow interface, (c) ice surface condition including the snow deposited on ice, and (d) wind-driven pressure pumping through the Published by Copernicus Publications on behalf of the European Geosciences Union
For (a), it is known that the air–sea ice CO2 flux is driven by the differences in pressure of CO2 (pCO2) between the sea ice surface and atmosphere (e.g., Delille et al, 2014; Geilfus et al, 2014)
Summary
Arctic sea ice is changing dramatically, with rapid declines in summer sea ice extent and a shift towards younger and thinner first-year ice rather than thick multi-year ice (e.g., Stroeve et al, 2012; Meier et al, 2014; Lindsay and Schweiger, 2015). Nomura et al (2013) proposed that snow properties (e.g., water equivalent) are important factors affecting gas exchange processes on sea ice. In addition, frost flowers (vapor-deposited ice crystals that wick brine from the sea ice surface) promote CO2 flux from the ice to the atmosphere (Geilfus et al, 2013; Barber et al, 2014; Fransson et al, 2015). These results were mainly found over land-based snow (soil and forest), and they are still poorly understood over sea ice (Papakyriakou and Miller, 2011)
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