Ice core impurities
The snow reaching central Greenland contains very low concentrations of impurities because most impurities have been removed by fall-out or precipitation during transport from the sources to the remote ice sheet. Yet, Greenland ice cores do contain small amounts of impurities that are important indicators of past climate conditions. Examples of such impurities are:
• Dust particles from deserts that are transported thousands of kilometres in the atmosphere
• Acids and ash particles from volcanic sources
• Sodium and Chloride ions that are indicators of past ocean activity and sea ice, and Ammonium that is related to biomass burning and forest fires
• Lead, Sulphate, and Nitrate from human-induced pollution
Ice core impurities can be measured by discrete sampling, where the ice core is cut into a large number of samples that are analyzed individually, or by so-called Continuous Flow Analysis, where a section of the ice core is melted on a hot plate and the impurities in the melt water are measured continuously in the stream of melted ice core.
When the impurity concentration of the ice is high, the impurities cause visible layers that are clearly visible to the naked eye. The image above shows dust layers in half a meter of Greenland ice core from the last glacial period deposited approximately 25.000 years ago. White layers contain dust and other impurities whereas black colour represents clear ice. The annual layers are 1-2 cm in thickness, so this ice was deposited over some 30 years.
Ice Core Drilling Projects