Laboratory study on coprecipitation of phosphate with ikaite in sea ice

Abstract

AbstractIkaite (CaCO3·6H2O) has recently been discovered in sea ice, providing first direct evidence of CaCO3 precipitation in sea ice. However, the impact of ikaite precipitation on phosphate (PO4) concentration has not been considered so far. Experiments were set up at pH from 8.5 to 10.0, salinities from 0 to 105, temperatures from −4°C to 0°C, and PO4 concentrations from 5 to 50 µmol kg−1 in artificial sea ice brine so as to understand how ikaite precipitation affects the PO4 concentration in sea ice under different conditions. Our results show that PO4 is coprecipitated with ikaite under all experimental conditions. The amount of PO4 removed by ikaite precipitation increases with increasing pH. Changes in salinity (S ≥ 35) as well as temperature have little impact on PO4 removal by ikaite precipitation. The initial PO4 concentration affects the PO4 coprecipitation. These findings may shed some light on the observed variability of PO4 concentration in sea ice.