EGU2020-7298, updated on 15 Feb 2021
https://doi.org/10.5194/egusphere-egu2020-7298
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Laser Ablation radiocarbon analysis of a high alpine stalagmite - a hint to an old organic carbon pool?

Caroline Welte1,2, Jens Fohlmeister3, Lukas Wacker1, Melina Wertnik1,2, Christoph Spötl4, Christiane Yeman1, Bodo Hattendorf5, Marcus Christl1, Timothy I. Eglinton2, and Hans-Arno Synal1
Caroline Welte et al.
  • 1Laboratory of Ion Beam Physics, ETH Zürich, 8093 Zurich, Switzerland
  • 2Geological Institute, ETH Zürich, 8092 Zurich, Switzerland
  • 3Potsdam Institute for Climate Impact Research (PIK) e.V., 14473 Potsdam, Germany
  • 4Institute of Geology, University of Innsbruck, Austria
  • 5Laboratory of Inorganic Chemistry, ETH Zürich, 8093 Zurich, Switzerland

A novel technique making use of laser ablation coupled online to accelerator mass spectrometry (LA-AMS) allows analyzing the radiocarbon concentration (F14C) in carbonate samples at a spatial resolution down to ~100 µm within very short analysis times [1]. This new technique can provide radiocarbon data close to the spatial resolution of stable carbon isotope measurements and, thus, can help to interpret δ13C signatures, which otherwise are difficult to understand [2]. Conventional analytical methods applied to stalagmite samples for 14C analysis, where a micro-sample is drilled or milled and carbon is liberated by the addition of phosphoric acid provide exclusively the isotope composition of the CaCO3, but not of organic matter also captured in stalagmites. LA-AMS allows accessing the 14C concentration of both materials opening up new opportunities for gaining insights into vegetation and soil dynamics.

SPA-127 is a stalagmite from Spannagel cave (W Austrian Alps) that grew between 8500 and 2500 a BP at an average rate of 25 μm/a [3]. δ13C and 14C were analyzed with high resolution along the full range of the 15 cm long specimen. During LA-AMS 14C analysis, positive anomalies in ion currents were observed in the older stalagmite section. These comparably higher CO2 conversion efficiencies are associated with organic materials compared to CaCO3 during LA. Lower F14C were observed along with these anomalies. The signal structure could be reproduced both after removing ~0.5 mm of the carbonate surface layer and on the stalagmite’s archive slab making possible contamination unlikely. So far, we deduce that the observed anomalies are caused by several flushing events in the early Holocene, in which 14C dead organic components (acids) entered the cave and were incorporated into the stalagmite matrix. Due to the high elevation of the cave and cold conditions during the glacial, the ancient organic acids most likely stem from the Eemian and were stored in the host rock.

[1] C. Welte, et al., (2016). Anal. Chem., 88, 8570– 8576.

[2] F. McDermott, (2004). Quat. Sci. Rev., 23, 901-918.

[3] Fohlmeister J. et al., (2013). Holocene, 23, 749–754.

 

How to cite: Welte, C., Fohlmeister, J., Wacker, L., Wertnik, M., Spötl, C., Yeman, C., Hattendorf, B., Christl, M., Eglinton, T. I., and Synal, H.-A.: Laser Ablation radiocarbon analysis of a high alpine stalagmite - a hint to an old organic carbon pool?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7298, https://doi.org/10.5194/egusphere-egu2020-7298, 2020

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