Past Climate and Biogeochemical Studies on Ice Cores (H. Fischer)
The climate of our planet is expected to change significantly within the next century due to the increasing greenhouse effect. Our expectations are mainly based on model calculations, but it is also possible to reconstruct the response of the global climate system to disturbances such as changing greenhouse gas concentrations, volcanos or changes in ocean circulation by investigating past global changes. Excellent archives of such changes are the polar ice sheets. The analyses of ice cores drilled in the central parts of the large ice sheets do not only allow us to reconstruct the local temperature, the annual precipitation rate or other regional environmental parameters but also the composition of the atmosphere in the past. This comprises both gaseous components (such as greenhouse gases, oxygen, nitrogen, etc.) as well as a large suite of chemical aerosol tracers. At CEP we study the full range of all these tracers using specialized analytical methods on ice cores from both Greenland and Antarctica. The oldest recovered ice reaches 800'000 years back in time and was drilled between 1999 and 2004 at Dome Concordia (Antarctica, 75°06'S/123°21'E).
CEP is one of the pioneers in studying the concentrations of the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in air enclosed as well as the isotopic composition (e.g. d13C of CO2 and d18O of O2) in air enclosed as bubbles or air hydrates in the ice. To measure the CO2 concentration an ice sample is mechanically crushed into small pieces in vacuum; the extracted air is measured using infrared absorption spectrometry. For the CH4 and N2O measurements we are melting the ice samples in an evacuated glass container and detect these gases using gas chromatography.
In recent years we pioneered the development of gas chromatography isotope ratio mass spectrometry methods to precisely quantify the full suite of isotopic ratios of all three greenhouse gases enclosed in polar ice cores (δ13CO2, δ18O(CO2), δ13CH4, δD(CH4), δ15N2O, δ18O(N2O)), with the goal to learn more about sources, sinks and exchange processes of these greenhouse gases. These analyses are complemented by isotopic studies on N2 , Ar and O2, which provide information on local temperature on the ice sheet and the oxygen cycle, respectively. Recently, we have extended our analytical portfolio within the ERC Advanced grant MATRICs by H. Fischer to measure precisely noble gas ratios and their isotopic signature, which provide information on global mean ocean temperature. In a second ERC Advanced Grant (deepSLice) H. Fischer and his group develop in collaboration with the group of L. Emmenegger at Empa a new Quantum Cascade Laser Spectrometry method for multicomponent greenhouse gas analyses on ice cores combined with a novel sublimation extraction system. This new method is targeted at obtaining the highest resolution greenhouse gas records in the deepest ice of a future Oldest Ice core covering the last 1.5 Myr of climate history.
With our Continuous Flow Analysis (CFA) system we are able to record continuous, highly resolved (< 1cm) concentration profiles of different chemical aerosol tracers incorporated in the ice. This is achieved by melting the ice samples continuously and analysing the meltwater online and simultaneously for the different chemical species. At the moment the following species can be measured routinely: H2O2, HCHO, NH4+, Ca2+, NO3-, Na+, particulate dust and electrolytic conductivity. In addition we developed techniques to quantify SO42-, total organic carbon, labile Fe and pH. Most of these tracers are analysed by fluorescence or absorption spectrometry. These measurements are often performed in the field directly after drilling the ice cores in order to prevent contamination during transport and storage.