Radim Štůsek and Lukáš Veselý performed a laboratory study of artificial seawater freezing. This was a topic of Radim’s bachelor thesis, and its results were finally published in impacted journal Science of the Total Environment. The authors discovered that the acidity of freeze-concentrated solution increases with decreasing temperature of the ice.
The samples of seawater were chosen to reflect natural conditions of seawater (3.5 % of salt weight and pH 8), frost flowers, and salty snow. The study focused on the investigation of acidity of the brine inside the ice vein (depicted in the abstract in the magnification on the right). The acidity was measured by the acid-base indicator present inside the ice veins. The study concluded that with decreasing temperature, the acidity of the brine increases above values that allow for efficient acid-base catalysis.
These results can explain the enhanced reactivity in the polar regions, both polluted by human-made chemicals and untouched pristine regions. The former was explained by scavenging of anthropogenic acids, however the latter remained as a mystery. This study finally cracked this mystery and proved that the sea ice can become acidic just by freezing by a completely natural mechanism. These results show that the anthropogenic acids are not necessary to facilitate the enhanced reactivity.