Radiocarbon and stable C isotope variability of two Holocene stalagmites from the high-alpine Spannagel Cave

Stable carbon (C) isotope records from stalagmites are readily available as they are often measured alongside stable oxygen isotopes (δ¹⁸O). Their interpretation, however, remains challenging due to several processes contributing to changes in the C-isotope ratio (e.g., fractionation, mixing). Spatially resolved radiocarbon (¹⁴C) data can help to interpret ¹³C signatures [1] but are rarely available due to expensive and time-consuming analysis. Rapid and continuous analysis of ¹⁴C concentration in carbonate samples at spatial resolution down to 100 μm has been recently made possible with the new LAAMS (laser ablation accelerator mass spectrometry) technique [2].

This novel technique has previously been applied to a Holocene stalagmite (SPA 127) from the high-alpine Spannagel Cave, Austria. Combined δ¹³C and ¹⁴C profiles (expressed as dead carbon fraction, dcf) allowed to hypothesize on the interplay of regional climate and contribution of an old organic C reservoir to stalagmite growth [3]. Here, we present LA-AMS results from a second Holocene stalagmite from Spannagel Cave (SPA 128). This stalagmite grew at a location close to that of SPA 127 with overlapping growth periods and consistent δ¹⁸O signals [4]. Both stalagmites show large and fast variations in the dcf and ^δ13C. SPA 128 has a generally higher dcf (with values above 60%) and a more negative δ¹³C signal that point towards contribution of an old organic C reservoir to the stalagmite C.

 

 

[1]D. Rudzka et al., (2011), GCA 75, 4321-4339.

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

[3] C. Welte et al., (2021), Clim. Past 17, 2165–2177.

[4] J. Fohlmeister et al., (2013), The Holocene 23, 749-754.