HIGH-RESOLUTION AMMONIUM ICE CORE RECORD COVERING A COMPLETE GLACIAL-INTERGLACIAL CYCLE

High-resolution ammonium measurements were performed along the Greenla nd Ice Core Program (GRIP) deep ice core, covering a complete climatic cycle. No overall anthropogenic increase is observed over the last 30 0 years; however, springtime concentrations have roughly doubled since 1950. Biomass burning is estimated to be a major source for ammonia e missions for preindustrial times. It contributes between 10% to 40% to the total ammonium deposited on the central Greenland ice sheet durin g the Holocene. No correlation is found between the ammonium summer co ncentrations recorded over the last 100 years and the area burned in n orthern North America, which is considered to be the main source area for ammonium deposited on the central Greenland ice sheet. This sugges ts that the meteorological factor is predominant for the pattern of am monium spikes observed in the ice core. If unchanged meteorological co nditions are assumed for the Holocene, as indicated by the delta(18)O ice record, a decreasing biomass burning activity toward present time can be derived from the ammonium ice record. Soil and vegetation emiss ions are responsible for the ammonium background concentrations in the ice. The record therefore may be used to trace back the biomass histo ry of the North American continent. A pronounced decreasing trend in b ackground ammonium is found during the Holocene, reflecting decreasing temperature and therefore lower NH3 emissions in the source region. V ariations in the ammonium concentration during the glacial age are dis cussed 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 w as built up immediately after the last interglacial and went through s everal large fluctuations during the last ice age.