The polar oceans stretching around our planet’s poles are permanently or temporarily covered with sea-ice. Because seawater has a higher salinity compared to freshwater, its freezing only begins when water temperature is approximately -3 to -4ºC (minus 3ºC to minus 4ºC). During the crystallization process, the seawater expels all salts and impurities, which concentrate at the surface of the newly formed ice or between the crystals. Recent studies in Antarctic and east Arctic polar oceans identified a rare hydrated calcium carbonate mineral, called ikaite (CaCO3·6H2O) among the products precipitated during freezing of cold seawater. During our Arctic cruise this year, team member Bogdan Onac is studying this mineral formation in ice.
Ikaite is a highly unstable mineral, which readily transforms into calcite (the most common and stable calcium carbonate mineral) if the temperature in the surrounding environment rises above 4ºC.
Since ikaite’s discovery in polar oceans sea ice, scientists are trying to understand whether its precipitation triggers changes in the pH and CO2 content of the sea surface waters. These issues are important in quantifying the amount of CO2 uptake by the ocean and when investigating the role played by the polar regions in the global carbon cycle.
During this polar expedition, samples of various types of sea ice are collected at different locations. The samples are stored in the refrigerator where they slowly melt at temperature below 2ºC to avoid transformation of ikaite into calcite. Once sea ice completely melts, Bogdan filters the meltwater through 2.0 µm filters. The filters are then studied under microscope in the refrigerator and samples of meltwater are collected for various physical, chemical, and biological analyses that Lisa Robbins and Jonathan Wynn are performing.