Description: The sediments recovered at ODP Sites 745 and 746 in the Australian-Antarctic Basin are characterized by cyclic facies changes between clayey diatom oozes and diatomaceous clays ranging in age from late Miocene (about 10 Ma) to Quaternary.The gravel and terrigenous sand content of the sediments is used as an indicator of the intensity of ice rafting through time. Maxima are recorded at 8.7-7.9, 6.6-6.0, 5.0-4.4, and 4.0-3.2 Ma. The maxima in more recent times are much less pronounced and occur at 2.4-1.6 and 1.4-1.0 Ma. All sand- and gravel-sized terrigenous sediment particles are of gneissic or granitic origin and originated from the East Antarctic continent. The maxima of ice rafting recorded at Sites 745 and 746 do not appear to represent local phenomena. Rather they document major advances and decays of the Antarctic ice shelves and glaciers and therefore represent events of great importance for the reconstruction of the paleoceanography of the Southern Ocean and the glacial history of Antarctica. In general, ice rafting was pronounced in the late Miocene and early Pliocene epochs, which are characterized by repeated ice advances and retreats. Ice rafting was less intensive during the late Pliocene to Quaternary time period, when ice shelves remained relative stable.The clay minerals indicate the fluctuating influence of different source areas on the delivery of fine-grained terrigenous sediment components. Part of this material may have been delivered from the Permian Amery Formation or from equivalents of this formation.

Description: To reveal the late Quaternary paleoenvironmental changes at the Antarctic continental margin, we test a lithostratigraphy, adjusted to a stable isotope record from the eastern Weddell Sea. The stratigraphy is used to produce a stacked sedimentological data set of eleven sediment cores. We derive a general model of glacio marine sedimentation and paleoenvironmental changes at the East Antarctic continental margin during the last two climatic cycles (300 kyr).The sedimentary processes considered include biological productivity, ice-rafting, current transport, and gravitational downslope transport. These processes are controlled by a complex interaction of sea-level changes and paleoceanographic and paleoglacial conditions in response to changes of global climate and local insolation. Sedimentation rates are mainly controlled by ice-rafting which reflects mass balance and behaviour of the Antarctic ice sheet. The sedimentation rates decrease with distance from the continent and from interglacial to glacial. Highest rates occur at the very beginning of interglacials, i.e. of oxygen isotope events 7.5, 5.5, and 1.1, these being up to five times higher than during glacials.The sediments can be classified into five distinct facies and correlated to different paleoenvironments: at glacial terminations (isotope events 8.0, 6.0, and 2.0), the Antarctic cryosphere adjusts to new climatic conditions. The sedimentary processes are controlled by the rise of sea level, the destruction of ice shelves, the retreat of sea-ice and the recommenced feeding of warm North Atlantic Deep Water (NADW) to the Circumpolar Deep Water (CDW). During peak warm interglacial periods (at isotope events 7.5, 7.3, 5.5., and 1.1), the CDW promotes warmer surface waters and thus the retreat of sea-ice which in turn controls the availability of light in surface waters. At distinct climatic thresholds local insolation might also influence sea-ice distribution. Primary productivity and bioturbation increase, the CCD rises and carbonate dissolution occurs in slope sediments also in shallow depth. Ice shelves and coastal polynyas favour the formation of very cold and saline Ice Shelf Water (ISW) which contributes to bottom water formation. During the transition from a peak warm time to a glacial (isotope stages 7.2-7.0, and 5.4-5.0) the superimposition of both intense ice-rafting and reduced bottom currents produces a typical facies which occurs with a distinct lag in the time of response of specific sedimentary processes to climatic change. With the onset of a glacial (at isotope events 7.0 and 5.0) the Antarctic ice sheet expands due to the lowering of sea-level with the extensive glaciations in the northern Hemisphere. Gravitational sediment transport becomes the most active process, and sediment transfer to the deep sea is provided by turbidity currents through canyon systems. During Antarctic glacial maxima (isotope stages between 7.0-6.0, and 5.0-2.0) the strongly reduced input of NADW into the Southern Ocean favours further advances of the ice shelves far beyond the shelf break and the continous formation of sea ice. Below ice shelves and/or closed sea ice coverage contourites are deposited on the slope.

Description: The upper Miocene to Pleistocene sediments recovered at ODP Sites 745 and 746 in the Australian-Antarctic Basin are characterized by cyclic facies changes. Sedimentological investigations of a detailed Quaternary section reveal that facies A is dominated by a high content of siliceous microfossils, a relatively low terrigenous sediment content, an ice-rafted component, low concentrations of fine sediment particles, and a relatively high smectite content. This facies corresponds to interglacial sedimentary conditions. Facies B, in contrast, is characteristic of glacial conditions and is dominated by a large amount of terrigenous material and a smaller opaline component. There is also a prominent ice-rafted component. The microfossils commonly are reworked and broken. The clay mineral assemblages show higher proportions of glacially derived illite and chlorite.A combination of four different processes, attributed to glacial-interglacial cycles, was responsible for the cyclic facies changes during Quaternary time: transport by gravity, ice, and current and changes in primary productivity. Of great importance was the movement of the grounding line of the ice shelves, which directly influenced the intensity of ice rafting and of gravitational sediment transport to the deep sea. The extension of the ice shelves was also responsible for the generation of cold and erosive Antarctic Bottom Water, which controlled the grain-size distribution, particularly of the fine fraction, in the investigated area.

Description: Vortrag zur Klima- und Polarforschung (Pressemitteilung)Mit der Verbrennung von Öl, Kohle und Gas hat die Menschheit unfreiwillig ein globales Klimaexperiment begonnen, dessen Tragweite bis heute nur schwer abzuschätzen ist. Der Vortrag versucht zum Verständnis der wichtigsten Prozesse, Zusammenhänge und Auswirkungen innerhalb des ungemein komplexen globalen Klimasystems beizutragen. Die speziellen Aufgaben und Ziele der Klimaforschung unter besonderer Berücksichtigung der Polargebiete werden an Beispielen aus den verschiedenen Bereichen naturwissenschaftlicher Grundlagenforschung dargestellt. Seit nunmehr 10 Jahren ist die Bundesrepublik verstärkt in der Polar- und Klimaforschung tätig. Koordinierendes

Description: Vortrag zur Klima- und Polarforschung vonDr. Hannes Grobe, Alfred-Wegener-Institut für Polar- und Meeresforschung (Pressemitteilung)Seit nunmehr 10 Jahren ist die Bundesrepublik verstärkt in der Polar- und Klimaforschung tätig. Koordinierendes Forschungszentrum ist das Alfred-Wegener-Institut für Polar- und Meeresforschung in Bremerhaven. Die vom Minister für Forschung und Technologie finanzierte Großforschungseinrichtung hat in den letzten Jahren international an Rang und Namen gewonnen. Hierzu hat nicht zuletzt das modernste und leistungsfähigste Forschungsschiff der Welt, die Polarstern, beigetragen.Besonders die Erforschung von Arktis und Antarktis wird als eines der letzten großen Abenteuer auf unserem Planeten angesehen. Sowohl für die Entstehung der Ozeane und Kontinente in ihrer heutigen Anordnung, als auch für das globale Klimageschehen kommt den Polargebieten eine Schlüsselrolle zu.Die Klimaforschung gewinnt durch die aktuellen Umweltprobleme unserer Zeit zunehmend an Bedeutung. Mit der Verbrennung von Öl, Kohle und Gas, ergänzt durch die Produktion noch weiterer klimarelevanter Treibhausgase, hat die Menschheit unfreiwillig ein globales Klimaexperiment begonnen, dessen Tragweite bis heute nur schwer abzuschätzen ist. Das Verständnis der wichtigsten Prozesse, Zusammenhänge und Auswirkungen innerhalb des ungemein komplexen globalen Klimasystems ist Voraussetzung für ein neues Umweltbewußtsein, das die Menschheit gezwungener Maßen in den nächsten Jahrzehnten entwickeln muß.Ergänzt durch Farbgrafiken und ungewöhnliche Aufnahmen aus den Polargebieten, werden die Aufgaben und Ziele der deutschen Polar- und Klimaforschung in einem Vortrag von Dr. Hannes Grobe, Geologe am Alfred-Wegener-Institut, am 30. Oktober 1992 in Bramstedt (Niedersachsenhaus - Heimatverein) vorgestellt.