Climatic implications of annual to decadal resolution stable isotope data from calcite varves of the Piànico interglacial lake record, Southern Alps

• Published in: Global and planetary change 2010-04, Vol.71 (3), p.168-174
• Main Authors: Mangili, Clara, Plessen, Birgit, Wolff, Christian, Brauer, Achim
• Format: Article
• Language: English
• Subjects: Calcite; endogenic calcite; Freshwater; Intervals; Isotopes; Lakes; Oscillations; oxygen isotopes; Piànico palaeolake; Sampling; sampling resolution; Sediments; Spectra; spectral analyses; Time series; varves
• ISSN: 0921-8181; 1872-6364
• DOI: 10.1016/j.gloplacha.2010.01.027

Stable oxygen isotope analyses at annual, 2-, 5-, 10- and 20-varve sample resolutions were carried out on two selected varve intervals from the interglacial sediment record of the Piànico palaeolake. These sediments are particularly suitable for ultra-high-resolution isotope analyses on lacustrine endogenic calcite because of the exceptionally well-preserved varve structure. A bias through detrital contamination can be excluded because microscopically controlled sampling enabled selecting detritus-free samples. The studied sediment intervals comprise 352 and 88 continuous varve series formed during periods of rapid climate change at the onset and end of a marked millennial-scale cool interval during the Piànico Interglacial. The most intriguing result is a pronounced short-term oscillation in the bi-annually resolved isotope record superimposed on the general decreasing and increasing δ 18O trends at the climatic transitions that is recorded at lower sample resolution. Spectral analyses of the bi-annual time series reveal periodicities indicating solar and NAO controls on the δ 18O record. Multiple δ 18O measurements from endogenic calcite of individual varves showed variations of up to 0.6‰, thus larger than the observed inter-annual variability and most likely explained by seasonal effects.