A high-resolution record of atmospheric 14C based on Hulu Cave speleothem H82

Southon, John; Noronha, Alexandra; Cheng, Hai; Edwards, R. Lawrence; Wang, Yongjin

doi:10.1016/j.quascirev.2011.11.022

Cited by 152 publications

(200 citation statements)

References 63 publications

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“…The authors noted large, short-term variations in DCF that were superimposed on a constant offset to the IntCal04 radiocarbon calibration curve for the period of overlap (w11e15 thousand years before present). A similar study, conducted by Southon et al (2012) from Hulu Cave, China, also highlighted a constant offset to the more recent IntCal09 curve (Reimer et al, 2009) and, in particular, observed a relatively stable DCF through known perturbations in regional hydrology, such as the Younger Dryas. On this basis, the authors were able to extend the calibration curve by assuming a stable DCF signal.…”

Section: Introductionmentioning

confidence: 61%

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

Griffiths

Fohlmeister

Drysdale

et al. 2012

Quaternary Geochronology

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a b s t r a c tOver the past decade, a number of speleothem studies have used radiocarbon ( 14 C) to address a range of palaeoclimate problems. These have included the use of the bomb pulse 14 C to anchor chronologies over the last 60 years, the combination of U-Th and 14 C measurements to improve the radiocarbon agecalibration curve, and linking atmospheric 14 C 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 14 C, 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 d 18 O, d 13 C and Mg/Ca values), and hence stronger summer monsoon. To explore this relationship, we used a geochemical soil-karst model coupled with 14 C 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 CO 2 , and ultimately led to a greater contribution of dead carbon from the bedrock.Published by Elsevier B.V.

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Section: Introductionmentioning

confidence: 61%

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

Griffiths

Fohlmeister

Drysdale

et al. 2012

Quaternary Geochronology

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“…The apparent stability of the offset between speleothem a 14 C and contemporaneous atmospheric a 14 CO 2 , commonly referred to as the dead carbon proportion (DCP), in some speleothems observed across major climate transitions has been both the most promising and puzzling result of attempts to produce speleothembased records of atmospheric a 14 C. Most exceptionally in the Hulu Cave speleothem, H82, DCP showed no response throughout the Younger Dryas despite the changes in summer monsoon intensity inferred from speleothem d 18 O, and vegetation changes inferred by pollen evidence (Southon et al, 2012). The hypothesis that some speleothems are formed predominately from CO 2 in the vadose zone derived from microbial decomposition of aged organic matter could potentially begin to explain the apparent stability of DCP in speleothems through major climate transitions.…”

Section: Implications For Interpretation Of Speleothem Carbon Isotopementioning

confidence: 99%

Radiocarbon evidence for decomposition of aged organic matter in the vadose zone as the main source of speleothem carbon

Noronha

Johnson

Southon

et al. 2015

Quaternary Science Reviews

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a b s t r a c tSeveral recent studies have used records of the radiocarbon ( 14 C) bomb peak in speleothems to inversely model the soil a 14 CO 2 and the age distribution of soil organic material (SOM) above caves, in part to investigate the potential of speleothems as sensitive records of past SOM dynamics. The results of these modeling studies have suggested that soil CO 2 at karst sites is derived primarily from the decomposition of SOM with turnover times on the order of decades to centuries. This result is in stark contrast with observations of soil a 14 CO 2 at non-karst sites, which indicate that soil CO 2 is derived primarily from root respiration and decomposition of SOM with much shorter turnover times. This discrepancy suggests that SOM in karst settings may have a very different age distribution than sites that have been studied previously and/or that soil CO 2 is not the main source of speleothem carbon. To help resolve this discrepancy, we present an improved inverse model which we use to estimate the age of CO 2 above several caves. We also present results from a detailed case study of soil carbon dynamics at Heshang Cave, China. This work demonstrates that SOM in karst sites may be much older than SOM in non-karst soils that have been studied previously, but that CO 2 produced in the shallow soil zone is unlikely to be the main source of speleothem carbon. A review of the literature suggests that the most likely explanation for the aforementioned discrepancy is that decomposition of down-washed SOM in the vadose zone is the dominant source of speleothem carbon.

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“…Beck et al, 2001;Weyhenmeyer et al, 2003;Dorale et al, 2008;McDermott et al, 2008;Hoffmann et al, 2010;Southon et al, 2012). Speleothems hold some key advantages over floating tree rings, varved chronologies, and marine records: (1) They can be precisely and absolutely dated using U-Th methods (Richards and Dorale, 2003); (2) Their fast growth rates, highly resolvable stratigraphy, and excellent preservation allow for often continuous highresolution 14 C measurement over the entire 14 C dating range; (3) they are widely used for paleoclimate reconstruction (Fairchild et al, 2006) so access to numerous U-Th dated samples is possible and will allow for replication of records and direct comparison with climate proxy data.…”

Section: Speleothem-based Records Of Atmospheric Radiocarbonmentioning

confidence: 99%

“…In natural systems, carbonate dissolution usually falls somewhere between the two end member scenarios, with average DCP around 15 ± 5% . Despite the potential for variable DCP to complicate speleothem-based reconstructions of atmospheric 14 C, speleothem radiocarbon records have been used to provide valuable constraints on the calibration curve during intervals where true atmospheric 14 C data is limited (Beck et al, 2001;Hoffmann et al, 2010;Southon et al, 2012).…”

Section: Speleothem-based Records Of Atmospheric Radiocarbonmentioning

confidence: 99%

“…The speleothem-based records of atmospheric 14 C that have been included in IntCal13 are a record spanning 10.6-26.8 ka from Hulu Cave, China (Southon et al, 2012), and a record spanning 11.1-44.1 from the Bahamas (Beck et al, 2001;Hoffmann et al, 2010). These records were constructed using a trench-and-wall sampling technique, where 14 C measurements on intact chips of calcite from the walls are interleaved with U-Th measurements on powder from drilled trenches, resulting in a robust and wellconstrained calendar chronology for the 14 C record.…”

Section: Speleothem-based Records Of Atmospheric Radiocarbonmentioning

confidence: 99%

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Assessing influences on speleothem dead carbon variability over the Holocene: Implications for speleothem-based radiocarbon calibration

Noronha¹,

Johnson²,

et al. 2014

Earth and Planetary Science Letters

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Recently, it has been shown that U-Th dated speleothems may provide a valuable archive of atmospheric radiocarbon ( 14 C), but the reliability of these records is dependent upon the stability of the dead carbon proportion (DCP) derived from the soil and bedrock. In order to assess climatic influences on speleothem DCP, we have investigated DCP variability over the Holocene interval where atmospheric 14 C is well known based on dendrochronologically dated tree rings by conducting 14 C measurements on a U-Th dated stalagmite (HS4) from Heshang Cave, Hubei Province, China (30 • 27 N, 110 • 25 E; 294 m) spanning 0.5-9.6 ka. We investigated climatic controls on DCP, and found that DCP in HS4 has an average value over the Holocene of 10.3 ± 1.5%, with an average age offset from atmospheric radiocarbon of 875 ± 130 years, and displays a response to both precipitation increases and decreases. HS4 DCP increases during the wetter mid-Holocene interval (∼5.5-7.1 ka), likely reflecting a shift to more closed-system dissolution in response to increased soil moisture. DCP decreases during the 8.2 ka event, a time period of dry conditions at Heshang Cave, though the lower amplitude of this shift indicates that DCP may be less sensitive to dry events. Speleothems are potentially valuable archives of atmospheric radiocarbon, especially in older portions of the 14 C calibration curve where knowledge of atmospheric 14 C is limited, however minor climatic influences on DCP could introduce uncertainties of several hundred years to calibrated ages.

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A high-resolution record of atmospheric 14C based on Hulu Cave speleothem H82

Cited by 152 publications

References 63 publications

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

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

Radiocarbon evidence for decomposition of aged organic matter in the vadose zone as the main source of speleothem carbon

Assessing influences on speleothem dead carbon variability over the Holocene: Implications for speleothem-based radiocarbon calibration

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