Stalagmite carbon isotopes and dead carbon proportion (DCP) in a near-closed-system situation: an interplay between sulphuric and carbonic acid dissolution

• Main Authors: Bajo, Petra, Borsato, Andrea, Drysdale, Russell, Hua, Quan, Frisia, Silvia, Zanchetta, Giovanni, Hellstrom, John, Woodhead, Jon
• Other Authors: The University of Newcastle. Faculty of Science, School of Environmental and Life Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon Press 2017
• Subjects: speleothem; dead carbon proportion (DCP); stable isotope ratios of carbon (δ¹³C); sulfuric acid dissolution; Corchia Cave; Carbonic acid
• Online Access: http://hdl.handle.net/1959.13/1348299

In this study, the ‘dead carbon proportion’ (DCP) calculated from combined U-Th and radiocarbon analyses was used to explore the carbon isotope systematics in Corchia Cave (Italy) speleothems, using the example of stalagmite CC26 which grew during the last ∼12 ka. The DCP values in CC26 are among the highest ever recorded in a stalagmite, spanning the range 44.8–68.8%. A combination of almost closed-system conditions and sulphuric acid dissolution (SAD) are proposed as major drivers in producing such a high DCP with minor contribution from old organic matter from the deep vadose zone. The long-term decrease in both DCP and δ¹³C most likely reflects post-glacial soil recovery above the cave, with a progressive increase of soil CO 2 contribution to the total dissolved inorganic carbon (DIC). Pronounced millennial-scale shifts in DCP and relatively small coeval but antipathetic changes in δ¹³C are modulated by the effects of hydrological variability on open and closed-system dissolution, SAD and prior calcite precipitation. Hence, the DCP in Corchia Cave speleothems represents an additional proxy for rainfall amount.