Carefully selected ice core data from Greenland can be used to reconstruct an annual proxy North Atlantic oscillation (NAO) index. This index for the past 350 years indicates that the NAO is an intermittent climate oscillation with temporally active (coherent) and passive (incoherent) phases. No indication for a single, persistent, multiannual NAO frequency is found. In active phases, most of the energy is located in the frequency band with periods less than about 15 years. In addition, variability on time scales of 80 to 90 years has been observed since the mid-19th century.

High‐resolution ammonium measurements were performed along the Greenland Ice Core Program (GRIP) deep ice core, covering a complete climatic cycle. No overall anthropogenic increase is observed over the last 300 years; however, springtime concentrations have roughly doubled since 1950. Biomass burning is estimated to be a major source for ammonia emissions for preindustrial times. It contributes between 10% to 40% to the total ammonium deposited on the central Greenland ice sheet during the Holocene. No correlation is found between the ammonium summer concentrations recorded over the last 100 years and the area burned in northern North America, which is considered to be the main source area for ammonium deposited on the central Greenland ice sheet. This suggests that the meteorological factor is predominant for the pattern of ammonium spikes observed in the ice core. If unchanged meteorological conditions are assumed for the Holocene, as indicated by the δ18O ice record, a decreasing biomass burning activity toward present time can be derived from the ammonium ice record. Soil and vegetation emissions are responsible for the ammonium background concentrations in the ice. The record therefore may be used to trace back the biomass history of the North American continent. A pronounced decreasing trend in background ammonium is found during the Holocene, reflecting decreasing temperature and therefore lower NH3 emissions in the source region. Variations in the ammonium concentration during the glacial age are discussed in terms of changes in transport and deposition mechanisms and changes in source strength, which can be related to the extent of the Laurentide ice sheet. The data suggest that the Laurentide ice sheet was built up immediately after the last interglacial and went through several large fluctuations during the last ice age.

A new deep core drilling operation started in 1990 in central Greenland and in 1992 reached the bottom at a depth of 3028 m.b. surface. Taking advantage of recent developments in the analytical technique of chemical trace species, continuous high resolution measurements of H20 2, HCHO, NH2 and Ca 2+ concentrations were performed directly on the ice core in the field. During the 1991 season all four components were measured simultaneously between 1300 m.b. surface and 2300 m.b. surface, corresponding to the time interval between 8000 and 38,000 years B.P. In this paper an overview of the results and our first interpretations in terms of climatic changes are given.

A continuous melting technique, combined with continuous flow analysis, has been developed for in situ measurements of chemical trace species in ice cores. A crosssection of 1.8 X 1.8 cm2 of the core is needed for the simultaneous analysis of at least four species. The subcore is melted continuously from one side, and only the inner, uncontaminated part of the melted sample is used for the analysis. The main advantage of this method as compared to conventional sampling and analysis procedures is given by a very high spatial resolution, combined with a significant reduction of sample handling work. The method can be applied for any species for which a sensitive continuous flow analysis method exists. This technique has been applied successfully for the parallel measurement of H2O2, HCHO, NH4+, and Ca2+ during the Greenland Ice Core Project (GRIP) deep drilling project at Summit, central Greenland (72°34' N, 37°38' W, 3200 m above mean sea level).