Journal cover Journal topic
The Cryosphere An interactive open-access journal of the European Geosciences Union
The Cryosphere, 10, 2173-2189, 2016
https://doi.org/10.5194/tc-10-2173-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
21 Sep 2016
Estimates of ikaite export from sea ice to the underlying seawater in a sea ice–seawater mesocosm
Nicolas-Xavier Geilfus1,2, Ryan J. Galley1, Brent G. T. Else3, Karley Campbell1, Tim Papakyriakou1, Odile Crabeck1, Marcos Lemes1, Bruno Delille4, and Søren Rysgaard1,2,5 1Centre for Earth Observation Science, University of Manitoba, Winnipeg, Canada
2Arctic Research Centre, Aarhus University, Aarhus, Denmark
3Department of Geography, University of Calgary, Calgary, Canada
4Unité d'Océanographie Chimique, Université de Liège, Liège, Belgium
5Greenland Climate Research Centre, Greenland Institute of Natural Resources, Nuuk, Greenland
Abstract. The precipitation of ikaite and its fate within sea ice is still poorly understood. We quantify temporal inorganic carbon dynamics in sea ice from initial formation to its melt in a sea ice–seawater mesocosm pool from 11 to 29 January 2013. Based on measurements of total alkalinity (TA) and total dissolved inorganic carbon (TCO2), the main processes affecting inorganic carbon dynamics within sea ice were ikaite precipitation and CO2 exchange with the atmosphere. In the underlying seawater, the dissolution of ikaite was the main process affecting inorganic carbon dynamics. Sea ice acted as an active layer, releasing CO2 to the atmosphere during the growth phase, taking up CO2 as it melted and exporting both ikaite and TCO2 into the underlying seawater during the whole experiment. Ikaite precipitation of up to 167 µmolkg−1 within sea ice was estimated, while its export and dissolution into the underlying seawater was responsible for a TA increase of 64–66 µmolkg−1 in the water column. The export of TCO2 from sea ice to the water column increased the underlying seawater TCO2 by 43.5 µmolkg−1, suggesting that almost all of the TCO2 that left the sea ice was exported to the underlying seawater. The export of ikaite from the ice to the underlying seawater was associated with brine rejection during sea ice growth, increased vertical connectivity in sea ice due to the upward percolation of seawater and meltwater flushing during sea ice melt. Based on the change in TA in the water column around the onset of sea ice melt, more than half of the total ikaite precipitated in the ice during sea ice growth was still contained in the ice when the sea ice began to melt. Ikaite crystal dissolution in the water column kept the seawater pCO2 undersaturated with respect to the atmosphere in spite of increased salinity, TA and TCO2 associated with sea ice growth. Results indicate that ikaite export from sea ice and its dissolution in the underlying seawater can potentially hamper the effect of oceanic acidification on the aragonite saturation state (Ωaragonite) in fall and in winter in ice-covered areas, at the time when Ωaragonite is smallest.

Citation: Geilfus, N.-X., Galley, R. J., Else, B. G. T., Campbell, K., Papakyriakou, T., Crabeck, O., Lemes, M., Delille, B., and Rysgaard, S.: Estimates of ikaite export from sea ice to the underlying seawater in a sea ice–seawater mesocosm, The Cryosphere, 10, 2173-2189, https://doi.org/10.5194/tc-10-2173-2016, 2016.
Publications Copernicus
Download
Short summary
The fate of ikaite precipitation within sea ice is poorly understood. In this study, we estimated ikaite precipitation of up to 167 µmol kg-1 within sea ice, while its export and dissolution into the underlying seawater was responsible for a TA increase of 64–66 μmol kg-1. We estimated that more than half of the total ikaite precipitated was still contained in the ice when sea ice began to melt. The dissolution of the ikaite crystals in the water column kept the seawater pCO2 undersaturated.
The fate of ikaite precipitation within sea ice is poorly understood. In this study, we...
Share