Dynamic ikaite production and dissolution in sea ice – control by temperature, salinity and pCO2 conditions

S. Rysgaard, F. Wang, R. J. Galley, R. Grimm, M. Lemes, N.-X. Geilfus, A. Chaulk, A. A. Hare, O. Crabeck, B. G. T. Else, K. Campbell, T. Papakyriakou (+3 others)
2013 The Cryosphere Discussions  
Ikaite is a hydrous calcium carbonate mineral (CaCO 3 · 6H 2 O). It is only found in a metastable state, and decomposes rapidly once removed from near-freezing water. 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 CO 2 exchange in ice-covered 5 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
more » ... e precipitation and dissolution in sea ice grown at an out-door pool of the Sea-ice Environmental Research Facility (SERF). During the experiment, ikaite precipitated in sea ice with temperatures below −3 • C, creating three distinct zones of ikaite concentrations: (1) a mm to cm thin surface layer 10 containing frost flowers and brine skim with bulk concentrations of > 2000 µmol kg −1 , (2) an internal layer with concentrations of 200-400 µmol kg −1 and (3) a bottom layer with concentrations of < 100 µmol kg −1 . Snowfall events caused the sea ice to warm, dissolving ikaite crystals under acidic conditions. Manual removal of the snow cover allowed the sea ice to cool and brine salinities to increase, resulting in rapid ikaite pre-15 cipitation. The modeled (FREZCHEM) ikaite concentrations were in the same order of magnitude as observations and suggest that ikaite concentration in sea ice increase with decreasing temperatures. Thus, varying snow conditions may play a key role in ikaite precipitation and dissolution in sea ice. This will have implications for CO 2 exchange with the atmosphere and ocean. Abstract 25 6078 TCD 7, 6075-6099, 2013
doi:10.5194/tcd-7-6075-2013 fatcat:yuq43aou2fhula75bwzesybty4