Preprints
https://doi.org/10.5194/tc-2017-226
https://doi.org/10.5194/tc-2017-226

  08 Dec 2017

08 Dec 2017

Review status: this preprint was under review for the journal TC but the revision was not accepted.

Quantification of calcium carbonate (ikaite) in first– and multi–year sea ice

Heather Kyle1,2, Søren Rysgaard1,2,3,4, Feiyue Wang2, and Mostafa Fayek1 Heather Kyle et al.
  • 1Department of Geological Sciences, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada
  • 2Centre for Earth Observation Science, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada
  • 3Arctic Research Centre, Aarhus University, 8000 Aarhus, Denmark
  • 4Greenland Climate Research Centre, Greenland Institute of Natural Resources, 3900 Nuuk, Greenland

Abstract. Ikaite (CaCO3•6H2O) is a metastable calcium carbonate mineral that forms at low temperature and/or high pressure. Ikaite precipitates in sea ice and may play a significant role in air–sea CO2 exchange in ice covered seas and oceans. However, the spatial and temporal dynamics of ikaite in sea ice are poorly understood due to few available measurements and time consuming analytical techniques. Here, we present a new method for quantifying ikaite in sea ice and compare it with a more time-consuming imaging technique currently in use. In short, sea ice cores were melted at low temperatures (< 4 °C), filtered for ikaite crystals that subsequently were dissolved and analyzed as dissolved inorganic carbon (DIC). The new method was applied on cores from experimental sea ice in Winnipeg (49° N), Canada, first–year sea ice near Cambridge Bay (69° N), Nunavut, Canada, and first– and multi–year sea ice near Station Nord (81° N), Greenland. Ikaite crystals were found in all sea ice types. The new ikaite quantification method is a straightforward technique that generally agrees with the image analysis technique and is both more accurate and precise. The DIC method may give lower concentrations in first–year ice and higher concentrations in multi–year ice than image analysis, likely due to the large spatial variability of ikaite crystals in first–year sea ice and the small crystal size in multi–year ice, both of which make quantification by image analysis more difficult. The new method showed high concentrations of ikaite in 20 cm thick young sea ice (335 µmol kg−1), lower concentrations in 1.5 m thick first–year sea ice (45 µmol kg−1) and low concentrations in 3.3 m thick multi–year sea ice (3 µmol kg−1). Highest concentrations were observed in the upper ice layers at all stations and layers where sea ice algae were present. The higher abundance of ikaite in young first–year sea ice indicates that its concentrations will likely increase in the Arctic as a result of the recent rapid decline of the multi–year ice cover and increasing presence of seasonal sea ice. As a result, it is likely that ikaite will play a more significant role in air–sea CO2 exchange in ice–covered seas in the future.

Heather Kyle et al.

 
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Heather Kyle et al.

Heather Kyle et al.

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Short summary
Ikaite may play a major role in air-sea carbon fluxes, but its importance is not well known due to difficulties with quantification. A new technique for measuring ikaite was developed and tested and our findings showed this method is effective. Sea ice properties were also measured. Results indicate that ikaite is most abundant in the upper layers of first-year sea ice so will likely play a more significant role in air-sea carbon fluxes in future as seasonal sea ice becomes more common.