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The Cryosphere An interactive open-access journal of the European Geosciences Union
The Cryosphere, 7, 707-718, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research Article
23 Apr 2013
Ikaite crystal distribution in winter sea ice and implications for CO2 system dynamics
S. Rysgaard1,2,3,4, D. H. Søgaard3,6, M. Cooper2, M. Pućko1, K. Lennert3, T. N. Papakyriakou1, F. Wang1,5, N. X. Geilfus1, R. N. Glud3,6,7, J. Ehn1, D. F. McGinnis6, K. Attard3,6, J. Sievers4, J. W. Deming8, and D. Barber1
1Centre for Earth Observation Science, Department of Environment and Geography, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
2Department of Geological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
3Greenland Climate Research Centre, Greenland Institute of Natural Resources, 3900 Nuuk, Greenland
4Arctic Research Centre, Aarhus University, 8000 Aarhus, Denmark
5Department of Chemistry, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
6University of Southern Denmark and NordCEE, Odense M, Denmark
7Scottish Association for Marine Science, Oban, UK
8University of Washington, School of Oceanography, Seattle, WA, USA

Abstract. The precipitation of ikaite (CaCO3 ⋅ 6H2O) in polar sea ice is critical to the efficiency of the sea ice-driven carbon pump and potentially important to the global carbon cycle, yet the spatial and temporal occurrence of ikaite within the ice is poorly known. We report unique observations of ikaite in unmelted ice and vertical profiles of ikaite abundance and concentration in sea ice for the crucial season of winter. Ice was examined from two locations: a 1 m thick land-fast ice site and a 0.3 m thick polynya site, both in the Young Sound area (74° N, 20° W) of NE Greenland. Ikaite crystals, ranging in size from a few μm to 700 μm, were observed to concentrate in the interstices between the ice platelets in both granular and columnar sea ice. In vertical sea ice profiles from both locations, ikaite concentration determined from image analysis, decreased with depth from surface-ice values of 700–900 μmol kg−1 ice (~25 × 106 crystals kg−1) to values of 100–200 μmol kg−1 ice (1–7 × 106 crystals kg−1) near the sea ice–water interface, all of which are much higher (4–10 times) than those reported in the few previous studies. Direct measurements of total alkalinity (TA) in surface layers fell within the same range as ikaite concentration, whereas TA concentrations in the lower half of the sea ice were twice as high. This depth-related discrepancy suggests interior ice processes where ikaite crystals form in surface sea ice layers and partly dissolve in layers below. Melting of sea ice and dissolution of observed concentrations of ikaite would result in meltwater with a pCO2 of <15 μatm. This value is far below atmospheric values of 390 μatm and surface water concentrations of 315 μatm. Hence, the meltwater increases the potential for seawater uptake of CO2.

Citation: Rysgaard, S., Søgaard, D. H., Cooper, M., Pućko, M., Lennert, K., Papakyriakou, T. N., Wang, F., Geilfus, N. X., Glud, R. N., Ehn, J., McGinnis, D. F., Attard, K., Sievers, J., Deming, J. W., and Barber, D.: Ikaite crystal distribution in winter sea ice and implications for CO2 system dynamics, The Cryosphere, 7, 707-718, doi:10.5194/tc-7-707-2013, 2013.
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