T133 Karst Ecosystems and Biogeochemistry

Monday, 16 October 2023
1:30 PM - 5:30 PM
310 / 311

COMBINING δ13C, RADIOCARBON, AND ELEMENTAL CHEMISTRY TO UNDERSTAND STABLE CARBON LARGE VARIATIONS IN STALAGMITE

Paper number: T133-6
Program: Technical Sessions
Time: 2:35 PM – 2:50 PM

Authors

Abstract

Stable carbon isotopes in stalagmite, δ13Cc, is one of the most complicated and difficult proxies to interpret in paleoclimate and paleoenvironmental studies because of its sensitivity to various local, regional, and global factors. For example, the large δ13Cc shift (~12‰, vs. VPDB) observed in several stalagmites from Anjohibe Cave, in northwestern Madagascar, around the late Holocene remains a subject of scientific study. Although it was previously assumed to reflect C3 to C4 vegetation cover change caused by anthropogenic activities, recent modern investigations inside the cave, at different locations, revealed a wide δ13Cc range of ~10‰ (vs. VPDB), a value that is comparable in its significance to the 12 ‰ mentioned above.

Here, we combine δ13C, radiocarbon (14C), and major and trace elements (MTE) as a proxy to provide additional insights about the possible non-vegetation drivers of δ13Cc. Our study uses two models, the CaveCalc model and the Fohlmeister model, to help our interpretation of the drip water evolution while it percolates down to the cave and precipitates CaCO3. The radiocarbon results, with values >100 pMC, demonstrate that the bomb peak, i.e., the pronounced increase in atmospheric 14C signals, are clearly recorded in these modern stalagmites. This suggests that the samples are younger than 1950 CE, and the soil carbon cycling has been fast without significant formation of aged soil organic matter. These radiocarbon results further suggests that stalagmites from Anjohibe Cave might be of use for future efforts to reconstruct past atmospheric 14C concentrations. Drip water geochemistry, δ13Cc and MTE, combined with two model simulations (CaveCalc and Fohlmeister model) suggests that the great δ13Cc range is best explained by the combined effects of the dissolved inorganic carbon residence time in the epikarst that affect the water-rock interaction and the rate of prior carbonate precipitation. This study therefore demonstrated how combined modeling and multi-proxy approaches can advance our understanding of the control mechanisms of δ13Cc for paleoclimate research.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-395958

© Copyright 2023 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.