Winter observations of CO2 exchange between sea ice and the atmosphere in a coastal fjord environment
J. Sievers1,3,L. L. Sørensen1,3,T. Papakyriakou5,B. Else7,M. K. Sejr2,3,D. Haubjerg Søgaard4,8,D. Barber5,and S. Rysgaard3,4,5,6J. Sievers et al.J. Sievers1,3,L. L. Sørensen1,3,T. Papakyriakou5,B. Else7,M. K. Sejr2,3,D. Haubjerg Søgaard4,8,D. Barber5,and S. Rysgaard3,4,5,6
1Department of Environmental Science, Aarhus University, 4000 Roskilde, Denmark
2Department of Bioscience, Aarhus University, 8600 Silkeborg, Denmark
3Arctic Research Centre, Aarhus University, 8000 Aarhus, Denmark
4Greenland Climate Research Centre, c/o Greenland Institute of Natural Resources box 570, Nuuk, Greenland
5Centre for Earth Observation Science, CHR Faculty of Environment Earth and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
6Department of Geological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
7Department of Geography, University of Calgary, Calgary, AB T2N 1N4, Canada
8Department of Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
1Department of Environmental Science, Aarhus University, 4000 Roskilde, Denmark
2Department of Bioscience, Aarhus University, 8600 Silkeborg, Denmark
3Arctic Research Centre, Aarhus University, 8000 Aarhus, Denmark
4Greenland Climate Research Centre, c/o Greenland Institute of Natural Resources box 570, Nuuk, Greenland
5Centre for Earth Observation Science, CHR Faculty of Environment Earth and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
6Department of Geological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
7Department of Geography, University of Calgary, Calgary, AB T2N 1N4, Canada
8Department of Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
Received: 26 Nov 2014 – Discussion started: 06 Jan 2015 – Revised: 11 Jun 2015 – Accepted: 08 Aug 2015 – Published: 25 Aug 2015
Abstract. Eddy covariance observations of CO2 fluxes were conducted during March–April 2012 in a temporally sequential order for 8, 4 and 30 days, respectively, at three locations on fast sea ice and on newly formed polynya ice in a coastal fjord environment in northeast Greenland. CO2 fluxes at the sites characterized by fast sea ice (ICEI and DNB) were found to increasingly reflect periods of strong outgassing in accordance with the progression of springtime warming and the occurrence of strong wind events: FCO2ICE1 = 1.73 ± 5 mmol m−2 day−1 and FCO2DNB = 8.64 ± 39.64 mmol m−2 day−1, while CO2 fluxes at the polynya site (POLYI) were found to generally reflect uptake FCO2POLY1 = −9.97 ± 19.8 mmol m−2 day−1. Values given are the mean and standard deviation, and negative/positive values indicate uptake/outgassing, respectively. A diurnal correlation analysis supports a significant connection between site energetics and CO2 fluxes linked to a number of possible thermally driven processes, which are thought to change the pCO2 gradient at the snow–ice interface. The relative influence of these processes on atmospheric exchanges likely depends on the thickness of the ice. Specifically, the study indicates a predominant influence of brine volume expansion/contraction, brine dissolution/concentration and calcium carbonate formation/dissolution at sites characterized by a thick sea-ice cover, such that surface warming leads to an uptake of CO2 and vice versa, while convective overturning within the sea-ice brines dominate at sites characterized by comparatively thin sea-ice cover, such that nighttime surface cooling leads to an uptake of CO2 to the extent permitted by simultaneous formation of superimposed ice in the lower snow column.
