High-precision C-14 measurements demonstrate production of in situ cosmogenic (CH4)-C-14 and rapid loss of in situ cosmogenic (CO)-C-14 in shallow Greenland firn

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dc.contributor.authorPetrenko, VVen_AU
dc.contributor.authorSeveringhaus, JPen_AU
dc.contributor.authorSmith, AMen_AU
dc.contributor.authorRiedel, Ken_AU
dc.contributor.authorBaggenstos, Den_AU
dc.contributor.authorHarth, CMen_AU
dc.contributor.authorOrsi, AJen_AU
dc.contributor.authorHua, Qen_AU
dc.contributor.authorFranz, Pen_AU
dc.contributor.authorTakeshita, Yen_AU
dc.contributor.authorBrailsford, Gen_AU
dc.contributor.authorWeiss, RFen_AU
dc.contributor.authorBuizert, Cen_AU
dc.contributor.authorDickson, Aen_AU
dc.contributor.authorSchaefer, Hen_AU
dc.date.accessioned2013-12-02T23:49:09Zen_AU
dc.date.available2013-12-02T23:49:09Zen_AU
dc.date.issued2013-03-01en_AU
dc.date.statistics2013-12-03en_AU
dc.description.abstractMeasurements of radiocarbon (C-14) in carbon dioxide (CO2), methane (CH4) and carbon monoxide (CO) from glacial ice are potentially useful for absolute dating of ice cores, studies of the past atmospheric CH4 budget and for reconstructing the past cosmic ray flux and solar activity. Interpretation of C-14 signals in ice is complicated by the fact that the two major C-14 components-trapped atmospheric and in situ cosmogenic-are present in a combined form, as well as by a very limited understanding of the in situ component. This study measured (CH4)-C-14 and (CO)-C-14 content in glacial firn with unprecedented precision to advance understanding of the in situ C-14 component. (CH4)-C-14 and (CO)-C-14 were melt-extracted on site at Summit, Greenland from three very large (similar to 1000 kg each) replicate samples of firn that spanned a depth range of 3.6-5.6 m. Non-cosmogenic C-14 contributions were carefully characterized through simulated extractions and a suite of supporting measurements. In situ cosmogenic (CO)-C-14 was quantified to better than +/- 0.6 molecules g(-1) ice, improving on the precision of the best prior ice (CO)-C-14 measurements by an order of magnitude. The (CO)-C-14 measurements indicate that most (>99%) of the in situ cosmogenic C-14 is rapidly lost from shallow Summit firn to the atmosphere. Despite this rapid C-14 loss, our measurements successfully quantified (CH4)-C-14 in the retained fraction of cosmogenic C-14 (to +/- 0.01 molecules g(-1) ice or better), and demonstrate for the first time that a significant amount of (CH4)-C-14 is produced by cosmic rays in natural ice. This conclusion increases the confidence in the results of an earlier study that used measurements of (CH4)-C-14 in glacial ice to show that wetlands were the likely main driver of the large and rapid atmospheric CH4 increase approximately 1 1.6 kyr ago. © 2013, Elsevier Ltd.en_AU
dc.identifier.citationPetrenko, V. V., Severinghaus, J. P., Smith, A. M., Riedel, K., Baggenstos, D., Harth, C., Orsi, A., Hua, Q., Franz, P., Takeshita, Y., Brailsford, G., Weiss, R. F., Buizert, C., Dickson, A., & Schaefer, H. (2013). High-precision C-14 measurements demonstrate production of in situ cosmogenic (CH4)-C-14 and rapid loss of in situ cosmogenic (CO)-C-14 in shallow Greenland firn. Earth and Planetary Science Letters, 365, 190-197. doi:10.1016/j.epsl.2013.01.032en_AU
dc.identifier.govdoc5258en_AU
dc.identifier.issn0012-821Xen_AU
dc.identifier.journaltitleEarth and Planetary Science Lettersen_AU
dc.identifier.pagination190-197en_AU
dc.identifier.urihttp://dx.doi.org/10.1016/j.epsl.2013.01.032en_AU
dc.identifier.urihttp://apo.ansto.gov.au/dspace/handle/10238/5057en_AU
dc.identifier.volume365en_AU
dc.language.isoenen_AU
dc.publisherElsevier Science BV.en_AU
dc.subjectGlaciersen_AU
dc.subjectGreenlanden_AU
dc.subjectAtmosphericsen_AU
dc.subjectCosmic ray fluxen_AU
dc.subjectCabon dioxideen_AU
dc.subjectExtractionen_AU
dc.titleHigh-precision C-14 measurements demonstrate production of in situ cosmogenic (CH4)-C-14 and rapid loss of in situ cosmogenic (CO)-C-14 in shallow Greenland firnen_AU
dc.typeJournal Articleen_AU
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