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
6Max Planck Institute for Meteorology, Hamburg, Germany
7Aarhus University, Department of Environmental Science, 4000 Roskilde, Denmark
Received: 07 Oct 2013 – Discussion started: 19 Dec 2013
Abstract. Ikaite (CaCO3 · 6H2O) is a metastable phase of calcium carbonate that normally forms in a cold environment and/or under high pressure. Recently, ikaite crystals have been found in sea ice, and it has been suggested that their precipitation may play an important role in air–sea CO2 exchange in ice-covered seas. Little is known, however, of the spatial and temporal dynamics of ikaite in sea ice. Here we present evidence for highly dynamic ikaite precipitation and dissolution in sea ice grown at an outdoor pool of the Sea-ice Environmental Research Facility (SERF) in Manitoba, Canada. During the experiment, ikaite precipitated in sea ice when temperatures were below −4 °C, creating three distinct zones of ikaite concentrations: (1) a millimeter-to-centimeter-thin surface layer containing frost flowers and brine skim with bulk ikaite concentrations of >2000 μmol kg−1, (2) an internal layer with ikaite concentrations of 200–400 μmol kg−1, and (3) a bottom layer with ikaite concentrations of <100 μmol kg−1. Snowfall events caused the sea ice to warm and ikaite crystals to dissolve. Manual removal of the snow cover allowed the sea ice to cool and brine salinities to increase, resulting in rapid ikaite precipitation. The observed ikaite concentrations were on the same order of magnitude as modeled by FREZCHEM, which further supports the notion that ikaite concentration in sea ice increases with decreasing temperature. Thus, varying snow conditions may play a key role in ikaite precipitation and dissolution in sea ice. This could have a major implication for CO2 exchange with the atmosphere and ocean that has not been accounted for previously.
Revised: 10 Jun 2014 – Accepted: 12 Jun 2014 – Published: 08 Aug 2014
Rysgaard, S., Wang, F., Galley, R. J., Grimm, R., Notz, D., Lemes, M., Geilfus, N.-X., Chaulk, A., Hare, A. A., Crabeck, O., Else, B. G. T., Campbell, K., Sørensen, L. L., Sievers, J., and Papakyriakou, T.: Temporal dynamics of ikaite in experimental sea ice, The Cryosphere, 8, 1469-1478, doi:10.5194/tc-8-1469-2014, 2014.