First estimates of the contribution of CaCO3 precipitation to the release of CO2 to the atmosphere during young sea ice growth

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Geilfus, Nicolas-Xavier, Carnat, Gauthier, Dieckmann, G.S., Halden, N, Nehrke, G, Papakyriakou, T, Tison, Jean-Louis, Delille, Bruno
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU) 2013
• Subjects: Physical; chemical; mathematical & earth Sciences; Earth sciences & physical geography; Physique; chimie; mathématiques & sciences de la terre; Sciences de la terre & géographie physique; Sea ice
• Online Access: https://orbi.uliege.be/handle/2268/147083; https://orbi.uliege.be/bitstream/2268/147083/1/Version%20soumises.pdf; https://doi.org/10.1029/2012JC007980

peer reviewed We report measurements of pH, total alkalinity, air-ice CO2 fluxes (chamber method) and CaCO3 content of frost flowers (FF) and thin landfast sea ice. As the temperature decreases, concentration of solutes in the brine skim (BS) increases. Along this gradual concentration process, some salts reach their solubility threshold and start precipitating. The precipitation of ikaite (CaCO3.6H2O) was confirmed in the FF and throughout the ice by Raman spectroscopy and X-ray analysis. The amount of ikaite precipitated was estimated to be 25 µmol kg-1 melted FF, in the FF and is shown to decrease from 19 µmol kg-1 to 15 µmol kg-1 melted ice in the upper part and at the bottom of the ice, respectively. CO2 release due to precipitation of CaCO3 is estimated to be 50 µmol kg-1 melted samples. The dissolved inorganic carbon (DIC) normalized to a salinity of 10 exhibits significant depletion in the upper layer of the ice and in the FF. This DIC loss is estimated to be 2069 µmol kg-1 melted sample and corresponds to a CO2 release from the ice to the atmosphere ranging from 20 to 40 mmol m-2 d-1. This estimate is consistent with flux measurements of air-ice CO2 exchange. Our measurements confirm previous laboratory findings that growing young sea ice acts as a source of CO2 to the atmosphere. CaCO3 precipitation during early ice growth appears to promote the release of CO2 to the atmosphere however its contribution to the overall release by newly formed ice is most likely minor.