Abstract
Important information about the past global climate is preserved in the Antarctic ice. This information becomes available from studying ice cores, where the change in the chemical composition of the past atmosphere is stored.
Although ice cores can provide valuable information over a large time span for major atmospheric components,
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to study the industrial period, the last 150 years, detailed measurements, measuring trace gases components of the past atmosphere, are required. In order to make the analyses of atmospheric trace gasses possible, large volumes of past air are needed. Large volumes of air can be taken from firn air. Firn air is the air that is trapped in the porous medium of firn, which is typically the first one hundred meters of an ice core.
In this thesis the firn air analyses of Site M in Dronning Maud Land, Antarctica (15°E, 75°S, 3453 m.a.s.l) are described. These firn air analyses were measured with gas chromatography, yielding concentration profiles with depth for a wide variety of trace gases. In the chapters three and four, the firn air analyses are focussed on the non-methane hydrocarbons (NMHCs): ethane, propane and acetylene, and methyl chloride. The NMHCs were studied because very little is known about their long-term and seasonal trend in the atmosphere around Antarctica and Southern Hemisphere in general whereas these NMHCs play an important role in the atmospheric oxidation chemistry. Studying the long-term and seasonal trend for methyl chloride is very interesting because this gas shows a large spatial variability although this is not expected because of its large lifetime.
In chapter three measurements are discussed obtaining a 25-year old record of trace gases. Naturally longer records are more valuable, particularly if pre-industrial levels can be recorded.
Although one would expect that old firn air could be found at locations high on the Antarctic plateau, with low temperatures, low accumulation rates and low surface pressures, firn air analyses on various locations showed that finding the oldest firn air is not straightforward. In chapter five a firn air diffusion model is combined with a meteorological data set of the Regional Atmospheric Climate Model for Antarctica (RACMO-ANT). To combine both models, site-specific parameters like: tortuosity, surface density and pore close-off density, were parameterised in terms of meteorological quantities. This was achieved with the measured data sets from ten firn air sites.
The diffusion model was applied to the entire Antarctic continent. This study yielded as mean result the location and age of the oldest firn air, being 156±22 years for the mean age of CO2 at pore close-off depth at 82°E, 83°S on the Antarctic plateau.
In chapter six, a new method of firn and ice core analyses is presented. In this chapter the chemical signature based on 16 trace elements, a chemical fingerprint, of an unknown 1500-year old volcanic horizon is measured with inductively coupled plasma mass spectrometry (ICP-MS). In chapter six it is for the first time that the trace metal chemistry is compared to the DEP record directly measured in the field. With the chemical fingerprint for the 1500-year old volcanic horizon, which has been scaled and normalised to allow comparison among various geochemical data, Mount Erebus is identified as a good candidate for the source.
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