Abstract: In order to estimate past changes in atmospheric NOx concentration, nitrate, an oxidation product of NOx, has often been measured in polar ice cores. In the frame of the European Project for Ice Goring in Antarctica (EPICA), a high-resolution nitrate record was obtained by continuous flow analysis (CFA) of a new deep ice core drilled at Dome C. This record allows a detailed comparison of nitrate with other chemical trace substances in polar snow under different climatic regimes. Previous studies showed that it would be difficult to make firm conclusions about atmospheric NOx concentrations based on ice core nitrate without a better understanding of the factors controlling NO3- deposition and preservation. At Dome C, initially high nitrate concentrations (over 500 ppb) decrease within the top meter to steady low values around 15 ppb that are maintained throughout the Holocene ice. Much higher concentrations (averaging 53 ppb) are found in ice from the Last Glacial Maximum (LGM). Combining this information with data from previous sampling elsewhere in Antarctica, it seems that under climatic conditions of the Holocene, temperature and accumulation rate are the key factors determining the NO3- concentration in the ice. Furthermore, ice layers with high acidity show a depletion of NO3-, but higher concentrations are found before and after the acidity layer, indicating that NO3- has been redistributed after deposition. Under glacial conditions, where NO3- shows a higher concentration level and also a larger variability, non-sea-salt calcium seems to act as a stabilizer, preventing volatilization of NO3- from the surface snow layers.

Abstract: The very successful application of a CFA (Continuous flow analysis) system in the GRIP project (Greenland Ice Core Project) for high-resolution ammonium, calcium, hydrogen peroxide, and formaldehyde measurements along a deep ice core led to further development of this analysis technique. We included methods for continuous analysis of sodium, nitrate, sulfate, and electrolytical conductivity, while the existing methods have been improved. The melting device has been optimized to allow the simultaneous analysis of eight components. Furthermore, a new melter was developed for analyzing firn cores. The system has been used in the frame of the European Project for Ice Goring in Antarctica (EPICA) for in-situ analysis of several firn cores from Dronning Maud Land, Antarctica, and for the new ice core drilled at Dome C, Antarctica.