MOLECULAR COMPOSITION OF DISSOLVED ORGANIC MATTER IN THE TALDICE ICE CORE

Introduction Deep polar ice cores are archives that collect information on paleoclimatic and paleoenvironmental conditions during glacial-interglacial swings. This information is then obtained by detailed analyses of the ice to obtain past temperature, greenhouse gas concentrations, and sea ice extent etc. The presence of trace chemicals in ice, reflect changes in their sources, transport, deposition, preservation. Methods An untargeted analysis of dissolved organic matter (DOM) provides a general over view of molecular species in the ice samples giving information on their sources and processes. For this kind of analysis typically 100 - 900 mL are required, this is not possible when dealing with deep ice cores. Using a nano-UPLC-nano-ESI-HRMS technique we have detected the major molecular species using only 4 ?L of melted ice. Results This work allowed us to tentatively identify generally aliphatic species, that were attributable mainly to the presence of saturated and unsaturated fatty acids, hydroxyl fatty acids and their degradation products, along with species from the oxidation of isoprene and monoterpenes and other compounds more difficult to interpret. Interglacial had more species while their number decreased in glacial samples. The reduction in oxidation products of isoprenes and monoterpenes is probably due temperature changes that affected terrestrial vegetation and the sea ice extent. Passing from interglacial to glacial times, unsaturated FAs almost disappeared because they are exposed for longer to oxidative processes. Conclusions Until now untargeted analyses have been limited to surface snow and shallow ice cores covering a short time span. To the best of our knowledge these are the first indications of the behavior of fatty acids and their oxidation products and the oxidation products of isoprene and monoterpenes in a deep ice core. Novel Aspect The innovative aspect of this work was the creation of a micro-volume analytical method that allowed the molecular characterization of DOM in a deep ice core.