Hydrological control of the dead carbon fraction in a Holocene tropical speleothem

Griffiths, M. L., Fohlrneister, J., Drysdale, R. N., Hua, Q., Johnson, K. R., Hellstrom, J. C., Gagan, M. K. and Zhao, J. -x. (2012) Hydrological control of the dead carbon fraction in a Holocene tropical speleothem. Quaternary Geochronology, 14 81-93. doi:10.1016/j.quageo.2012.04.001

Author Griffiths, M. L.
Fohlrneister, J.
Drysdale, R. N.
Hua, Q.
Johnson, K. R.
Hellstrom, J. C.
Gagan, M. K.
Zhao, J. -x.
Title Hydrological control of the dead carbon fraction in a Holocene tropical speleothem
Journal name Quaternary Geochronology   Check publisher's open access policy
ISSN 1871-1014
Publication date 2012-12
Year available 2012
Sub-type Article (original research)
DOI 10.1016/j.quageo.2012.04.001
Volume 14
Start page 81
End page 93
Total pages 13
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Collection year 2013
Language eng
Formatted abstract
Over the past decade, a number of speleothem studies have used radiocarbon (14C) to address a range of palaeoclimate problems. These have included the use of the bomb pulse 14C to anchor chronologies over the last 60 years, the combination of U-Th and 14C measurements to improve the radiocarbon age-calibration curve, and linking atmospheric 14C variations with climate change. An issue with a number of these studies is how to constrain, or interpret, variations in the amount of radioactively dead carbon (i.e. the dead carbon fraction, or DCF) that reduces radiocarbon concentrations in speleothems. In this study, we use 14C, stable-isotopes, and trace-elements in a U-Th dated speleothem from Flores, Indonesia, to examine DCF variations and their relationship with above-cave climate over the late Holocene and modern era. A strong association between the DCF and hydrologically-controlled proxy data suggests that more dead carbon was being delivered to the speleothem during periods of higher cave recharge (i.e. lower δ18O, δ13C and Mg/Ca values), and hence stronger summer monsoon. To explore this relationship, we used a geochemical soil-karst model coupled with 14C measurements through the bomb pulse to disentangle the dominant components governing DCF variability in the speleothem. We find that the DCF is primarily controlled by limestone dissolution associated with changes in open- versus closed-system conditions, rather than kinetic fractionation and/or variations in the age spectrum of soil organic matter above the cave. Therefore, we infer that periods of higher rainfall resulted in a higher DCF because the system was in a more closed state, which inhibited carbon isotope exchange between the karst water dissolved inorganic carbon and soil-gas CO2, and ultimately led to a greater contribution of dead carbon from the bedrock.
Keyword Radiocarbon
Dead carbon fraction
U-Th dating
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ
Additional Notes Available online: 12 April 2012.

Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2013 Collection
Centre for Microscopy and Microanalysis Publications
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