Oceanic circulation modes of the Glacial-Interglacial cycle - high resolution measurements of Neodymium isotopes on Atlantic IODP/ODP sediment cores.

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It is supposed that in the global interplay of hemispheres either the deep water production in the North or in the South Atlantic dominated, having direct and significant influence on the heat budget of the respective hemisphere. Although great efforts have been undertaken in order to reconstruct the past of the extremely climate relevant Atlantic Ocean, it has so far not been possible to identify the role of the ocean circulation as cause or consequence of the in part dramatic climate fluctuations which have taken place in the past 100,000 years. The branch of research considering these questions, the palaeoceanography, faces two essential problems here: On the one hand , the methods used often have weaknesses and limited applicability, especially tracers which take part in the nutrient cycle and are subject to diagenetic processes. On the other hand the temporal and spacial coverage of existing measurements allows only for limited conclusions which may deliver local information which cannot be extrapolated to a global scale. In order to come to reliable results about the oceanic past of heat transport and the distribution of carbon and nutrients it is necessary to collect a high amount of data. The material provided from the IODP/ODP core repositories represents a unique fundament for this work. In the younger past the measurement of the neodymium isotope ratio 143Nd/144Nd emerged as method of choice. The distinct isotopic signatures of water masses originating in the Pacific and the North Atlantic Deep Water render neodymium a unique tracer for the ocean circulation in the Atlantic. The neodymium signature and with it the mixing ratio of the prominent water masses in the past is preserved in ferromanganese accretions in the sediment. The appraoch of careful separation of these accrections from the bulk sediment and the subsequent measurement of their neodymium isotopy serves as a methodology which is, applied on a large scale, uttermost promising. It is applicable wherever there are cores available, it is reliably measurable with modern standard mass spectrometers and the chemical treatment of the sample material is relatively fast and cost-efficient, if the respective experience and the knowledge of the chemical work steps exist. Therefore, using selected IODP/ODP cores the question of the timings of water mass transitions in the Atlantic shall be pursued. It shall be clarified how fast these transitions took place and in which global climatological phase which circulation pattern was prominent. With the aid of box models and the comparison with further tracers (231Pa/230Th, d13C) a comprehensive image of the past glacial-interglacial cycle shall be drawn, allowing inference of the crucial feedback effects and interactions in the climate system, which are directly necessary for the improvement and validation of climate models.