High-resolution fast ion chromatography (FIC) measurements of chloride, nitrate and sulphate along the EPICA Dome C ice core Rita TRAVERSI, Silvia BECAGLI, Emiliano CASTELLANO, Alessio MIGLIORI, Mirko SEVERI, Roberto UDISTI Department of Chemistry, University of Florence, I-50019 Sesto F.no (Florence), Italy E-mail: rita.traversi@unifi.it ABSTRACT . Fast ion chromatographic (FIC) analysis of the first European Project for Ice Coring in Antarctica (EPICA) Dome C ice core (788 m deep) was used to obtain high-resolution profiles for Cl ^ , NO 3 ^ and SO 4 2^ , spanning the last 45000 years. About 19 000 determinations for each component, with an average resolution of 4.0 cm, were per- formed in the field on continuously melted firn- and ice-core sections. The measured core covers the Holocene, the glacial/interglacial transition and about one-third of the last ice age. In the glacial period, mean concentrations of 93.8, 24.4 and 178.4 mgL ^1 were cal- culated for Cl ^ , NO 3 ^ and SO 4 2^ , respectively. The mean levels significantly increase in the Last Glacial Maximum (LGM), when these compounds reach values of 149.6, 53.9 and 219.3 mgL ^1 . During the glacial/interglacial transition, the mean concentrations quickly decrease reaching the typical Holocene values of 19.1, 12.9 and 93.3 mgL ^1 , for Cl ^ , NO 3 ^ and SO 4 2^ , respectively. All species settle on Holocene-like values about 4000 years before the beginning of the warm period (from the isotopic curve) showing a low (chloride) and no (nitrate and sulphate) sensitivity to Antarctic Cold Reversal climatic change.The sulphate decrease is consistent with the dilution factor due to the higher accu- mulation rate in the interglacial conditions (about 2.5), suggesting no significant change in source intensity or transport efficiency occurred for this component. On the contrary, the Holocene values for chloride and nitrate, being much lower than those measured in the LGM, suggest a source-intensity and transport-efficiency enhancement during the LGM and/or a more effective fixing of HCl and HNO 3 in the snow layers through the neutraliz- ing effect of the higher atmospheric dust load. 1. INTRODUCTION A reliable understanding of the processes involved in climatic change at regional or global scale is closely related to the pos- sibility of obtaining long-time, high-resolution records of cli- matic and environmental direct indicators or proxy-markers. In this way, the forcing factors and the negative or positive feedback mechanisms of the climatic system can be studied and effectively interpreted. To do this, it is essential to have available natural archives able to provide palaeoclimatic and palaeoenvironmental data over the longest period and with the highest time resolution possible. Among the natural palaeo-data archives, ice cores appear to constitute the best compromise between the maximum temporal range and the minimum sampling interval, at least for detailed studies of environmental and climatic changes in the last-glacial/inter- glacial cycles (Bradley and Eddy,1991). To obtain continuous, time-resolved palaeo-datasets, it is necessary to analyze ice-core sections with a depth resolution of a few centimetres. This means that a very large number of subsamples has to be produced, making the analytical work tedious, time-consuming and expensive. In the 1980s, some relevant parameters, such as liquid or solid (electrical conduc- tivity measurements (ECM) and dielectric profiling (DEP)) conductivity, were continuously measured in the field (Hammer, 1980; Moore and others, 1989), but chemical analysis was carried out on single subsamples, leading to many contamination problems, mainly caused by sample manipulation. The fast, high-resolution determination of chemical compounds, carried out in series with drilling activ- ity and subsampling, allows an immediate interpretation of temporal profiles of climatic and environmental markers, pro- vides a useful indication for a reliable subsampling (driving a higher-resolution sampling where the profile trends look particularly interesting), identifies temporal horizons (e.g. volcanic signatures) and reveals post-depositional processes affecting the stratigraphic distribution of some species. Recently, chemical flow analysis (CFA) methods, based on continuous ice-core melting followed by spectrofluorimetric and spectrophotometric flow analysis, have been developed and used for measurements in the field (Fuhrer and others, 1993; Sigg and others, 1994; RÎthlisberger and others, 2000b). Nevertheless, some ionic components, especially chloride and sulphate, were not measured (chloride) or were partially determined (sulphate), because the continuous methods at present do not have sufficient sensitivity to determine low levels. To overcome this information gap, we set up a semi-continuous ion chromatographic method (Udisti and others, 2000), named fast ion chromatography (FIC), able to carry out one deter- mination of chloride, nitrate and sulphate every minute. In Annals of Glaciology 35 2002 # International Glaciological Society 291