Effect of ikaite precipitation on phosphate removal in sea ice

Abstract

Ikaite (CaCO3·6H2O) precipitation in sea ice has been shown to affect CO2 exchange between the atmosphere and ocean. A laboratory study indicates that it could also co-precipitate phosphate from sea ice, which has the potential to affect sea-ice biogeochemical processes. However, the relative importance of ikaite precipitation on phosphate removal under sea-ice conditions remains unknown. We investigated ikaite precipitation in both frost flowers and seaice (under two scenarios: flooded by seawater and non-flooded) in an outdoor sea-ice mesocosm experiment, and in sea ice under natural conditions in north-eastern Greenland. The ice mesocosm experiment showed that ikaite was highly enriched in frost flowers with a concentration of up to 350 µmol·kg–1. Ikaite was also detected in the surface layer of sea ice, ranging from ca. 13 µmol·kg–1 in the non-flooded ice to ca. 95 µmol·kg–1 in the flooded ice. However, under all these conditions, no phosphate co-precipitation with ikaite was observed. The field study in Greenland showed similar results: ikaite was detected in surface ice with an average concentration of 13.8 µmol·kg–1, but no phosphate removal due to ikaite precipitation was observed. These results suggest that the impact of ikaite precipitation on phosphate and the sea-ice ecosystem might not be as significant as imagined previously.

Keywords

• co-precipitation
• surface ice
• frost flowers
• greenland