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UP: Umweltphysik

UP 23: Atmosph
äre und Klima

UP 23.1: Fachvortrag

Mittwoch, 15. März 2006, 16:30–16:45, D

Laboratory experiments to determine the fractionation of stable isotopes in speleothems — •Denis Scholz, Elke Wiedner, Augusto Mangini, and Ricardo März — Heidelberger Akademie der Wissenschaften, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany

Recent studies have shown that speleothems are a promising archive for past climate. Stalagmites can be dated very precisely with the Th/U method and stable isotopes that can be measured at a spatial resolution corresponding to few years of growth, respond very sensitively to climate changes. We performed a series of laboratory experiments to study the fractionation of oxygen and carbon isotopes during the precipitation of carbonate with the aim to better understand the non-equilibrium precipitation of calcite, which most often is met in natural speleothems. Carbonate was precipitated under controlled conditions both from a body of standing water and from a solution flowing along a rod. Slow degassing of CO₂ produced a carbonate with δ¹⁸O values in equilibrium with the solution, but with a significant enrichment of δ¹³C which was inversely proportional to the height of the solution. The resulting slope of Δδ¹⁸O/Δδ¹³C was 0. Fast degassing of CO₂ along the rod at a relative humidity of 100