Description: During the I997-98 Italian Antarctic Programme (PNRA) summer season, two snow pits were dug 3km north-westward of the ltalian-French Dome C Station (East Antarctica, 75o 09'S, 123o 06'E, 3200m a.s.l.) and the EPICA project drilling site. These 4 m depth pits were done upwind of the station to avoid the risk of pollution. In the first pit, after cleaning of walls, a high resolution sampling was carried out for chemical (anions, cations, organic acids), stable isotope ( d 180 and d D), tritium and dust (concentration, size distribution, AI concentration) measurements. In the second pit, dug 50cm apart, visual stratigraphy was done. The concentration/depth profiles and any eventual correlation between chemical components were examined to obtain environmental information about primary and secondary aerosol sources, transport phenomena and any evidence of relevant trends in the temporal series of some components. Particular attention was spent on the relative contribution of sea spray components (Na+, Cl-, Mg2+) and substances from biogenic origin (nssSO42- and MSA) to atmospheric aerosol. Using Na+ and MSA as source tracers, fractionating phenomena induced variations of CI-/Na+ and nssSO42-/MSA ratios were valued. nssSO42-/MSA relationship with MSA reveals the importance of long range transport effects and the presence of other nssSO42- sources. Temporal data series for Ca2+, K+, No3-, F- and some short chain carboxylic acids are also reported. For almost all the components ng/g or sub-ng/g concentration levels were found, as expected for a station located at a very long distance from the most part of aerosol sources and at high altitude. Tritium analyses were carried out in order to identify the peak related to the thermonuclear tests performed in the atmosphere in the early sixties as a reference horizon for dating purpose. The seasonal signal in the stable isotopes was not observed due to the low accumulation of this site, but nevertheless the main trends were compared to other Antarctic sites and to temperature records available from the main East Antarctica automatic weather stations. The dust concentration, size distribution (Particles Counter) and AI (Atomic Absorption) measurements show records of continental influences on the Dome C insoluble aerosols. The very low annual accumulation rate, 3 to 3.5 cm (W.E.) and, probable, wind erosion are the main reasons of the absence of seasonal variations. Because of this limitation, of more interest is the correlation of the measured records with the visual stratigraphy. The main topics from these pits measurements can provide: 1) the sutdy of the last tens years of atmospheric deposition in the Dome C area, 2) define the atmosphere-snow transport processes, also on the comparison with EPICA ice core, 3) identification of primary and secondary sources at this site.

Description: The Biesenthal Basin formed by thawing of dead ice, is located at the northern rim of the Bamim Plateau north of Berlin; in it sedimentary processes varied considerably during the Late Weichsel Glacial Period. Their variations are reflected in sedimentary fabrics, grain size distributions and repeated overprinting of surface textures on quartz grains. The glacifluviolimnic, Iimnic and aeolian sediments were deposited on the shore of a periglacial water within the area shaped by the last glacial advance; presently it is located at the border between lowlands and plateau. The sedimentary sequence is characterized by variations and deformations at the scale of micrometers, hence the present study focussed on microfabric analysis.

Description: Im grönländischen Inlandeis sind wegen ihrer unterschiedlichen optischen Eigenschaften Sommer- und Winterschichten visuell zu unterscheiden. Dies wurde zur Datierung u.a. des GISP2 Kerns bis etwa 50 000 BP in Kombination mit anderen Datierungsverfahren benutzt (ALLEY et al., 1997). 1996 setzte das Alfred-Wegener-Institut eine line-scan Kamera zur Dokumentation des NGRIP Eiskernes ein. Die aus diesen Aufnahmen gewonnenen Grauwertprofile, die ein Maß für die Bildhelligkeit in Abhängigkeit von der Kernteufe sind, zeigen Schwankungen, die mit entsprechenden durch visuelle stratigraphische Beobachtung gefundenen Schichten korrespondieren. Die Ursache für unterschiedliche Bildhelligkeit liegt im unterschiedlichen Streu- und Absorptionsvermögen der Eisschichten. Um von der Kernoberfläche ausgehende Störungen auszuschalten wurden line-scan Aufnahmen an hierfür speziell präparierten planparallelen Kernschnitten durchgeführt. Die Bildhelligkeit korreliert mit der Kristallgröße, die an Dünnschnitten der selben Kernsequenzen ermittelt wurde. Die Möglichkeiten des Einsatzes von line-scan und Schlitzkameras zur Erfassung der Eiskernstratigraphie werden anhand von Daten aus grönländischen und antarktischen Eiskernen (NGRIP, Dome C) aufgezeigt. Die Ergebnisse werden mit anderen jahreszeitlich schwankenden Daten (elektrische Leitfähigkeit aus DEP-Messungen u. a.) verglichen und die Möglichkeiten und Grenzen einer teilweise automatisierten Eiskerndatierung mit optischen Methoden diskutiert. ALLEY et al., Visual-stratigraphic dating of the GISP2 ice core: Basis, reproducibility, and application. J. Geophys. Res. 102, C12 (1997), p. 26,367-26,381