Radiocarbon Measurements and Annual Rings in Cave Formations

Broecker, Wallace S.; Olson, Edwin A.; Orr, Phil C.

doi:10.1038/185093a0

Cited by 69 publications

(47 citation statements)

References 3 publications

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“…Some of the earliest speleothem research employed 14 C as a dating tool (Broecker et al, 1960;Hendy and Wilson, 1968), but up until recently it has played a very minor role in speleothem research because of the 'dead carbon' problem. This problem stems from the inclusion of bedrock-derived, 'radioactively dead' carbon into the total dissolved inorganic carbon (DIC) pool that is subsequently encoded into a growing speleothem.…”

Section: Introductionmentioning

confidence: 99%

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: 99%

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

Griffiths

Fohlmeister

Drysdale

et al. 2012

Quaternary Geochronology

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“…Franke (1951), Franke et al (1959), Broecker at al. (1960), Hendy and Wilson (1968), and Geyh and Franke (1970) were among the first who used 14 C embedded in stalagmites calcite to date speleothems.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Soil Organic Matter Age Spectrum on the Reconstruction of Atmospheric ¹⁴C Levels Via Stalagmites

2011

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ABSTRACT. The imprint of the radiocarbon bomb peak was detected in the top of stalagmite ER-77 from Grotta di Ernesto (NE Italy). This recently grown stalagmite reveals a reservoir age, also known as dead carbon fraction (dcf), of ~1050 14 C yr, or 12%. By applying a 14 C soil-karst model, the age spectrum of soil organic matter (SOM) as well as the CO 2 contribution of the single SOM reservoirs to the total soil CO 2 can be derived. Under the assumption of constant vegetation, meaning both vegetation density and the age spectrum of SOM, it is possible to derive the soil-air 14 C activity of the past using the 14 C calibration curve (IntCal04). Hence, it is also possible to calculate an artificial stalagmite 14 C data set covering the last 25,000 yr with parameters determined for stalagmite ER-77. With this artificially constructed data set, we derived the hypothetical atmospheric 14 C activity by using the common method of applying a constant dcf on the modeled 14 C data set of the stalagmite. This theoretical approach allows to analyze the impact of a constant and variable SOM age spectrum on atmospheric 14 C reconstructions performed with real stalagmite 14 C measurements. We observe deviations between IntCal04 and the atmospheric 14 C activity as derived with our modeled 14 C data set, which are larger for older SOM than for younger SOM and vary in time up to 2 pMC, depending on the strength of the variations in the atmospheric 14 C level. This value is comparable with the 1- uncertainty given by IntCal04 for the last glacial. For a varying SOM age spectrum, the deviations between the calibration curve and 14 C level of the atmosphere reconstructed with a stalagmite exceed 3 pMC, which is larger than the 1- uncertainty of IntCal04. In general, the SOM has smoothing, shifting, and 14 C-depleting effects on the stalagmite 14 C record and, therefore, on the stalagmite-derived atmospheric 14 C activity. In this study, changes in soil-air pCO 2 and carbonate dissolution conditions, which have also an important impact on the 14 C record of a stalagmite, are not accounted for.

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“…It had been occupied by palaeo Indians on and off for at least 8,000 years. I obtained a 14 C date of 7830 ± 350 years on fragments of netting from the lowest habitation level (Broecker and Orr, 1958;Broecker et al, 1960c). As a budding geologist, my interest was in the history of the lake itself.…”

Section: Figure 4bmentioning

confidence: 99%

The Carbon Cycle and Climate Change: Memoirs of my 60 years in Science

Broecker¹

2012

geochempersp

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Radiocarbon Measurements and Annual Rings in Cave Formations

Cited by 69 publications

References 3 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

The Influence of Soil Organic Matter Age Spectrum on the Reconstruction of Atmospheric ¹⁴C Levels Via Stalagmites

The Carbon Cycle and Climate Change: Memoirs of my 60 years in Science

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Radiocarbon Measurements and Annual Rings in Cave Formations

Cited by 69 publications

References 3 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

The Influence of Soil Organic Matter Age Spectrum on the Reconstruction of Atmospheric 14C Levels Via Stalagmites

The Carbon Cycle and Climate Change: Memoirs of my 60 years in Science

Contact Info

Product

Resources

About

The Influence of Soil Organic Matter Age Spectrum on the Reconstruction of Atmospheric ¹⁴C Levels Via Stalagmites