Toward a radiometric ice clock: uranium ages of the Dome C ice core

Aciego, S.; Bourdon, Bernard; Schwander, Jakob; Baur, H.; Forieri, A.

doi:10.1016/j.quascirev.2011.06.008

Cited by 45 publications

(43 citation statements)

References 35 publications

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“…This means of estimating the recoil ejection factor has yielded ice core ages (based on the accumulation of 238 U decay recoil products from dust trapped within the ice) comparable to independently obtained ages (Aciego et al, 2011).…”

Section: Recoil Loss Factor F Amentioning

confidence: 67%

Sediment residence times constrained by uranium-series isotopes: A critical appraisal of the comminution approach

Handley

Turner

Afonso

et al. 2013

Geochimica et Cosmochimica Acta

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Cohen, T. (2013). Sediment residence times constrained by uranium-series isotopes: a critical appraisal of the comminution approach. Geochimica et Cosmochimica Acta, 103 (N/A), 245-262. Sediment residence times constrained by uranium-series isotopes: a critical appraisal of the comminution approach AbstractQuantifying the rates of landscape evolution in response to climate change is inhibited by the difficulty of dating the formation of continental detrital sediments. We present uranium isotope data for Cooper Creek palaeochannel sediments from the Lake Eyre Basin in semi-arid South Australia in order to attempt to determine the formation ages and hence residence times of the sediments. To calculate the amount of recoil loss of 234U, a key input parameter used in the comminution approach, we use two suggested methods (weighted geometric and surface area measurement with an incorporated fractal correction) and typical assumed input parameter values found in the literature. The calculated recoil loss factors and comminution ages are highly dependent on the method of recoil loss factor determination used and the chosen assumptions. To appraise the ramifications of the assumptions inherent in the comminution age approach and determine individual and combined comminution age uncertainties associated to each variable, Monte Carlo simulations were conducted for a synthetic sediment sample. Using a reasonable associated uncertainty for each input factor and including variations in the source rock and measured (234U/238U) ratios, the total combined uncertainty on comminution age in our simulation (for both methods of recoil loss factor estimation) can amount to ±220-280 ka. The modelling shows that small changes in assumed input values translate into large effects on absolute comminution age. To improve the accuracy of the technique and provide meaningful absolute comminution ages, much tighter constraints are required on the assumptions for input factors such as the fraction of α-recoil lost 234Th and the initial (234U/238U) ratio of the source material. In order to be able to directly compare calculated comminution ages produced by different research groups, the standardisation of pre-treatment procedures, recoil loss factor estimation and assumed input parameter values is required. We suggest a set of input parameter values for such a purpose. Additional considerations for calculating comminution ages of sediments deposited within large, semi-arid drainage basins are discussed. AbstractQuantifying the rates of landscape evolution in response to climate change is inhibited by the difficulty of dating the formation of continental detrital sediments. We present uranium isotope data for Cooper Creek palaeochannel sediments from the Lake Eyre Basin in semi-arid South Australia in order to attempt to determine the formation ages and hence residence times of the sediments. To calculate the amount of recoil loss of 234 U, a key input parameter used in the comminution approach, we use two suggested methods (weighted geome...

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Section: Recoil Loss Factor F Amentioning

confidence: 67%

Sediment residence times constrained by uranium-series isotopes: A critical appraisal of the comminution approach

Handley

Turner

Afonso

et al. 2013

Geochimica et Cosmochimica Acta

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“…Also U / Th dating has been developed for ice cores and applied to the EDC ice core. This provided accurate ages, however, the error is on the order of 25 % for 800 000 yr old ice and becomes substantially larger for 1.5 million yr (Aciego et al, 2011). Absolute age markers are also provided by maxima in the 10 Be deposition flux caused by anomalous 10 Be production rates during geomagnetic anomalies.…”

Section: Future Reconnaissance Studiesmentioning

confidence: 99%

Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core

et al. 2013

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Abstract. The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful presite selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, we strongly suggest significantly reduced ice thickness to avoid bottom melting. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 Myr old ice (i.e., more than 700 m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, Published by Copernicus Publications on behalf of the European Geosciences Union. H. Fischer et al.:Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice.

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“…At present, the comminution method appears to yield relatively trustworthy absolute ages where sediment provenance is relatively simple, fine-grained sediment is formed rapidly and where sediment transport and storage are limited (e.g., glacially produced sediment deposited in the Kings River Fan, California; Lee et al, 2010) or where the sediments are subject to minimal post-depositional weathering (e.g., dust trapped in ice sheets; Aciego et al, 2011). However, this study suggests that the comminution approach has, at present, limited applicability and accuracy for sediment deposited within catchments involving of multiple sediment sources and proven non-secular equilibrium source material.…”

Section: Discussionmentioning

confidence: 99%

“…The most commonly employed methods are at present based upon either a weighted geometric estimation (DePaolo et al, 2006) using sample grain size distributions and assumptions for surface roughness and grain aspect ratio, or measurements of specific surface area (e.g., Brunauer-Emmett-Teller (BET) gas adsorption measurements) with an incorporated fractal correction Aciego et al, 2011) to account for the significant difference between the size of the adsorbed gas molecule (commonly N 2 : 0.354 nm) and the recoil length scale (~20-50 nm; Hashimoto et al, 1985;Ziegler, 1996) (see the appendix for fα calculation equations and input parameter details). As pointed out by previous authors of the few comminution studies undertaken so far (e.g., Lee et al, 2010;Handley et al, in press) the technique holds significant potential, but much more work is required before it can be considered as an accurate dating tool.…”

Section: Comminution Age Theorymentioning

confidence: 99%

“…The comminution dating approach utilises 234 U-238 U disequilibrium in fine-grained sediments attributed to recoil loss of 234 U (see Section 2 for details). U-series recoil-loss dating has yielded reasonable timescale estimates when compared to independently constrained ages (e.g., Aciego et al, 2011), but can be offset by several 100 ka (Lee et al, 2010). Therefore, further testing and consideration of the methodology is required to improve the accuracy of ages produced and prove its value as a dating technique.…”

Section: Introductionmentioning

confidence: 99%

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Considerations for U-series dating of sediments: Insights from the Flinders Ranges, South Australia

Handley¹,

Turner²,

Dosseto³

et al. 2013

Chemical Geology

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Uranium isotope ratios have been determined for the fine-grained detrital fraction of Pleistocene Wilkawillina valley-fill sediments, four local Proterozoic bedrock samples and fine-grained aeolian material from a sand dune deposit of the Flinders Ranges, South Australia. The aim was to quantify the comminution age, i.e. the time elapsed since physical weathering of the bedrock, and residence time of the valley-fill sediments and to place tighter constraints on input parameters for the comminution age calculation. Despite using two independent approaches for determination of the recoil lost fraction of 234U from the sediment (weighted geometric and surface area estimates), samples fail to produce realistic comminution ages and hence, residence times. The issues involved in the ability to determine sediment comminution ages are discussed. The (234U/238U) activity ratio of the local bedrock is not in secular equilibrium, despite the bedrock being much older than 1Ma, i.e. the timeframe for 234U and 238U to reach secular equilibrium in a closed system. Using the average Flinders Ranges bedrock (234U/238U) ratio instead of an assumed (234U/238U) activity ratio of unity for the source would significantly reduce calculated residence times. This result warrants concern for future studies using the comminution approach for which a secular equilibrium source (234U/238U) activity ratio is assumed. Significant input of aeolian material may modify the measured (234U/238U) activity ratios. Such input may be more tightly constrained in future studies using rare earth element and radiogenic isotopic data. Future comminution studies would benefit from further consideration of the importance of 1) leaching lost 234U from source rock and bulk sediment samples, 2) wind deposition of fine-grained material and 3) the appropriateness and robustness of sample pre-treatment procedures. AbstractUranium isotope ratios have been determined for the fine-grained detrital fraction of Pleistocene Wilkawillina valley-fill sediments, four local Proterozoic bedrock samples and fine-grained aeolian material from a sand dune deposit of the Flinders Ranges, South Australia. The aim was to quantify the comminution age, i.e. the time elapsed since physical weathering of the bedrock, and residence time of the valley-fill sediments and to place tighter constraints on input parameters for the comminution age calculation. Despite using two independent approaches for determination of the recoil lost fraction of 234 U from the sediment (weighted geometric and surface area estimates), samples fail to produce realistic comminution ages and hence, residence times. The issues involved in the ability to determine sediment comminution ages are discussed. The ( 234 U/ 238 U) activity ratio of the local bedrock is not in secular equilibrium, despite the bedrock being much older than 1 Ma, i.e. the timeframe for 234 U and 238 U to reach secular equilibrium in a closed system. Using the average Flinders Ranges bedrock ( 234 U/ 238 U) ratio instead of an ass...

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Toward a radiometric ice clock: uranium ages of the Dome C ice core

Cited by 45 publications

References 35 publications

Sediment residence times constrained by uranium-series isotopes: A critical appraisal of the comminution approach

Sediment residence times constrained by uranium-series isotopes: A critical appraisal of the comminution approach

Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core

Considerations for U-series dating of sediments: Insights from the Flinders Ranges, South Australia

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Toward a radiometric ice clock: uranium ages of the Dome C ice core

Cited by 45 publications

References 35 publications

Sediment residence times constrained by uranium-series isotopes: A critical appraisal of the comminution approach

Sediment residence times constrained by uranium-series isotopes: A critical appraisal of the comminution approach

Where to find 1.5 million yr old ice for the IPICS &quot;Oldest-Ice&quot; ice core

Considerations for U-series dating of sediments: Insights from the Flinders Ranges, South Australia

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Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core