The Renland ice core. A Northern Hemisphere record of aerosol composition over 120,000 years

Abstract

The Renland ice core from East Greenland covers a full glacial cycle from the Holocene into the previous Eem interglacial. The first northern hemispheric record of both anions (Cl^-, NO₃^-, SO₄^2-, CH₃SO₃^-), cations (Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺), total amount of insoluble dust and acidity (measured as solid electrical conductivity) is extracted from this ice core in continuous profiles between 10 and 120 ka b.p. and from the 19th century. The ions measured are in balance during the interglacials but there is a large deficiency of anions during the glacial period. The ice is alkaline during most parts of the glacial period and Ca²⁺ is the totally dominating ion therefore the deficiency of anions is probably due to carbonates (not measured). The concentration of most impurities is higher during glacial stages than the interglacials. The largest increase is found for crustally derived impurities (up to a factor of 10) while the sea salt elements are only slightly enhanced (less than a factor of 2). The concentration of impurities with a strong biogenic component is generally lower during glacial stages than the interglacials. A simple model tests the effect of changes in the physical conditions of the atmosphere influencing transport and deposition processes while keeping the source area and production rate constant. The model results show that the increased glacial concentrations observed for some impurities can be explained entirely by changes in transport and deposition, while the decrease in others may indicate a change in source emissions. The total content of impurities in the glacial atmosphere is higher if physical changes in the atmosphere rather than source emission changes are responsible for the variations observed in the Renland ice core. Thus, physical changes in the atmosphere can have a large impact on the radiative properties of the atmosphere and a climate forcing mechanism may be found in the dynamics of the atmosphere. However, a better understanding of the hydrological cycle and the general circulation of the atmosphere during glacial conditions has to be attained to be able to interpret influences on the global climate of a changed composition of the atmosphere from ice core data.