First estimates of the contribution of CaCO3precipitation to the release of CO2to the atmosphere during young sea ice growth

Abstract

AbstractWe report measurements of pH, total alkalinity, air‐ice CO2fluxes (chamber method), and CaCO3content of frost flowers (FF) and thin landfast sea ice. As the temperature decreases, concentration of solutes in the brine skim 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−1melted FF, in the FF and is shown to decrease from 19 to 15 µmol kg−1melted ice in the upper part and at the bottom of the ice, respectively. CO2release due to precipitation of CaCO3is estimated to be 50 µmol kg−1melted 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−1melted sample and corresponds to a CO2release 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 CO2exchange. Our measurements confirm previous laboratory findings that growing young sea ice acts as a source of CO2to the atmosphere. CaCO3precipitation during early ice growth appears to promote the release of CO2to the atmosphere; however, its contribution to the overall release by newly formed ice is most likely minor.