Detecting changes in climate and atmospheric composition with tracers in Arctic ice caps

Abstract: Changes in climate and atmospheric composition over decades to a hundred thousand years have been studied by extracting records of various tracers from two Arctic ice cores. A seven metre long ice core of superimposed ice was recovered from the Storöya ice cap in north-eastern Svalbard. The annual increments of superimposed ice were identified by combining records of ice texture, ice structure, insoluble particle content and solid electrical conductivity. A net balance record over the time period A.D. 1954 to 1979 was established and the obtained information about past local climate is found to agree with observations. The chemical composition of the insoluble particles was examined but only limited information is gained about atmospheric aerosol composition due to the disturbed deposition record as is found in superimposed ice.The records from a 325 metre long surface-to-bedrock ice core from the Renland ice cap, East Greenland, cover a full glacial cycle into the previous interglacial Eem 130 000 years B.P. Changes in climate are revealed by the record of stable oxygen isotopes. Fast and large variations in temperature between glacial and interglacial periods, but also in mid and late parts of the last glaciation, are found in agreement with other Greenland deep ice cores. The precipitation rate is found to vary significantly between different climatic regimes. Comparison with records from Antarctica suggests a roughly parallel climatic development in the two hemispheres. Changes in the composition of the atmospheric aerosol have been studied by extracting the first Northern Hemisphere record of major anions, major cations, insoluble dust and acidity over a full climatic cycle. The concentration in the ice of most impurities is higher in cold glacial stages. However, for impurities with a strong biogenic component (nitrate, ammonium and methanesulphonate) the concentration is lower in cold glacial stages which is opposite to Southern Hemisphere records. The ammonium record has been utilised to discuss source areas of the greenhouse gas methane. High ammonium concentrations in mild glacial stages are found to coincide with high global concentrations of methane, which points to the terrestrial biosphere at high northern latitudes as a possible source. A simple model simulation indicates that concentration changes in the ice of one order of magnitude between different climatic regimes can be explained entirely by changes in the hydrological cycle and the general circulation of the atmosphere. These physical changes of the atmosphere affects the radiation balance of the atmosphere, just as changes in source emissions, by strongly changing the airborne concentration and composition of the atmospheric aerosol.