Natural Abundances of Carbon Isotopes (¹⁴C,¹³C) in Lichens and Calcium Oxalate Pruina: Implications for Archaeological and Paleoenvironmental Studies

Abstract

ABSTRACT. Radiocarbon ages of calcium oxalate that occurs naturally on rock surfaces have been used recently in archaeological and paleoenvironmental studies. Oxalate rock coatings are found globally, with most appearing to be residues from epilithic lichens. To explore the source(s) of carbon used by these organisms for the production of oxalate we measured the natural abundances of 14 C and 13 C in 5 oxalate-producing lichen species, 3 growing on limestone in southwestern Texas and 2 on sandstone in Arkansas. We also examined the distribution of the isotopes between the calcium oxalate and lichen tissues by separating these components and measuring the 13 C/C independently. The results demonstrate that the limestone species were slightly enriched in 14 C, by 1.7‰, relative to the sandstone species, which suggests that "dead" carbon from the limestone substrate does not constitute a significant source of carbon for the production of oxalate. The calcium oxalate produced by the lichens is also enriched in 13 C by 6.5‰ compared to the lichen tissues, demonstrating that there is a large carbon isotope discrimination during oxalate biosynthesis. These results support the reliability of 14 C ages of calcium oxalate rock coatings used for archaeological and paleoclimate studies.

Changes in size and composition of pigweed (Amaranthus hybridus L.) calcium oxalate crystals under CO2 starvation conditions

“…Concerning the isolated crystals, in all treatments (including the control), the δ 13 C content was considerably higher than that of any biomass sample, suggesting lower 13 C discrimination during the formation of the CaOx crystals compared to the bulk of organic carbon independent of the treatment. This result (see also Tooulakou et al ) agrees with previous findings in isolated crystals of other plant species (Rivera and Smith , Raven et al ) and CaOx pruina of lichens (Beazley et al ). One reason for the difference in stable isotope composition between crystals and biomass could be the use of carbon transferred from the root during restoration of the crystals.…”

Calcium oxalate AMS 14C dating and chronology of post-Palaeolithic rock paintings in the Iberian Peninsula. Two dates from Abrigo de los Oculados (Henarejos, Cuenca, Spain)

“…There are several hypotheses on the origin of calcium oxalate coatings, ranging from results of human activity (Rampazzi, 2004), to metabolic action of lichens, bacteria and microbes inhabiting the outer layers of rock faces (Beazley et al, 2002;Hess et al, 2007;Krumbein et al, 2003). It has also been proposed that pictographs may sometimes abet the formation of these crusts, due to bacteria and fungi feeding on chemical components of the paint (Cole and Watchman, 2005).…”

Stable carbon isotope analyses show dominance of C3 grasses in the feed selected by small herbivores at the alpine meadow at the Tibetan Plateau

“…The muscle stable carbon isotopic data suggest that it is reasonable to use small mammals to reveal the abundance and distribution of different photosynthetic pathway grasses within the ecosystem. Stable isotope analyses of plant and animal tissues are providing additional methods to study modern ecological systems (Rundel et al, 1989;Yi et al, 2003b;Li et al, 2004a;Yi, 2005a,b;Yi and Zhang, 2005) even paleoecology (Cormie and Schwarcz, 1994;Jahren et al, 1998;Boutton et al, 1999;Franz-Odendaal et al, 2002;Beazley et al, 2003).…”