Pakitsoq Greenland Younger Dryas-Preboreal 14CH4 Data ----------------------------------------------------------------------- World Data Center for Paleoclimatology, Boulder and NOAA Paleoclimatology Program ----------------------------------------------------------------------- NOTE: PLEASE CITE ORIGINAL REFERENCE WHEN USING THIS DATA!!!!! NAME OF DATA SET: Pakitsoq Greenland Younger Dryas-Preboreal 14CH4 Data LAST UPDATE: 10/2011 (Original receipt by WDC Paleo) CONTRIBUTORS: Petrenko, V.V., A.M. Smith, E.J. Brook, D. Lowe, K. Riedel, G. Brailsford, Q. Hua, H. Schaefer, N. Reeh, R.F. Weiss, D. Etheridge, and J.P. Severinghaus IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2011-136 WDC PALEO CONTRIBUTION SERIES CITATION: Petrenko, V.V., et al. 2011. Pakitsoq Greenland Younger Dryas-Preboreal 14CH4 Data. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series # 2011-136. NOAA/NCDC Paleoclimatology Program, Boulder CO, USA. ORIGINAL REFERENCE: Petrenko, V.V., A.M. Smith, E.J. Brook, D. Lowe, K. Riedel, G. Brailsford, Q. Hua, H. Schaefer, N. Reeh, R.F. Weiss, D. Etheridge, and J.P. Severinghaus. 2009. 14CH4 Measurements in Greenland Ice: Investigating Last Glacial Termination CH4 Sources. Science, Vol. 324, pp. 506-508, 24 April 2009. 10.1126/science.1168909 ABSTRACT: The cause of a large increase of atmospheric methane concentration during the Younger Dryas-Preboreal abrupt climatic transition (~11,600 years ago) has been the subject of much debate. The carbon-14 (14C) content of methane (14CH4) should distinguish between wetland and clathrate contributions to this increase. We present measurements of 14CH4 in glacial ice, targeting this transition, performed by using ice samples obtained from an ablation site in west Greenland. Measured 14CH4 values were higher than predicted under any scenario. Sample 14CH4 appears to be elevated by direct cosmogenic 14C production in ice. 14C of CO was measured to better understand this process and correct the sample 14CH4. Corrected results suggest that wetland sources were likely responsible for the majority of the Younger Dryas–Preboreal CH4 rise. ADDITIONAL REFERENCES: Brook, E.J., S. Harder, J. Severinghaus, E.J. Steig, and C.M. Sucher. 2000. On the origin and timing of rapid changes in atmospheric methane during the last glacial period. Global Biogeochem. Cycles 14, 559-572. Lal, D., K. Nishiizumi, and J.R. Arnold. 1987. In-situ cosmogenic H-3, C-14, and Be-10 for determining the net accumulation and ablation rates of ice sheets. J.Geophys. Res., 92 (B6), 4947-4952 Petrenko, V.V., J.P. Severinghaus, E.J. Brook, J. Mühle, M. Headly, C. Harth, H. Schaefer, N. Reeh, R. Weiss, D.C. Lowe, and A.M. Smith. 2008a. A novel method for obtaining very large ancient air samples from ablating glacial ice for analyses of methane radiocarbon. Journal of Glaciology 54, 233-44. Petrenko, V.V., A.M. Smith, G. Brailsford, K. Riedel, Q. Hua, D. Lowe, J.P. Severinghaus, V. Levchenko, T. Bromley, R. Moss, J. Muhle, and E.J. Brook, 2008b. A new method for analyzing C-14 of methane in ancient air extracted from glacial ice. Radiocarbon 50, 53-73. Van Der Kemp, W., C. Alderliesten, K. Van Der Borg, A. De Jong, R. Lamers, J. Oerlemans, M. Thomassen, and R. Van De Wal, R. 2002. In situ produced C-14 by cosmic ray muons in ablating Antarctic ice. Tellus B 54, 186-192. GEOGRAPHIC REGION: Greenland PERIOD OF RECORD: FUNDING SOURCES: US National Science Foundation (NSF) grants OPP0221470 and OPP0221410, Packard Fellowship, American Chemical Society grant PRF 42551-AC2, ANSTO Cosmogenic Climate Archives of the Southern Hemisphere project, New Zealand Foundation of Science and Technology (contract C01X0703), Australian Climate Change Science Program. DESCRIPTION: 14C measurements in large-volume ice samples from Pakitsoq, West Greenland. This data set contains measurements of 14C of methane made on ancient air extracted from large-volume glacial ice samples spanning the Younger Dryas - Preboreal climatic transition about 11,600 years ago. The data set also contains supporting measurements of 14C of carbon monoxide and 14C of carbon dioxide. The measurements were made to test the hypothesis that catastrophic destabilization of marine methane clathrates caused the methane increase at the end of the Younger Dryas. The results suggested little to no change in 14CH4 over the time of the methane increase, arguing against major clathrate involvement. The ice samples were collected between Jul 1 and Aug 15, 2005. INSTRUMENT AND METHOD DESCRIPTION The field and analytical system for determinations of 14CH4 in large-volume glacial ice samples have been described in (Petrenko et al., 2008a; Petrenko et al., 2008b; Petrenko et al., 2009). This system involves the melt-extraction of occluded air from very large volumes of glacial ice or at the sampling / ice coring site. Briefly, the present field system consists of a large chemically polished aluminum vacuum melting tank (~670 L internal volume) and a series vacuum and transfer pumps. The ice is loaded into the tank, and the headspace is evacuated and flushed 3x with either ultra-high purity (UHP) air, nitrogen or argon. The ice is then melted, releasing the ancient air into the headspace. The air is then extracted from the tank by clean diaphragm transfer pumps and stored in electropolished stainless steel canisters for further laboratory handling and analyses. In the laboratory, the air is first processed through a system that converts either CH4 or CO to CO2, and captures this CO2 for further handling. In the case of CH4 processing, H2O, CO2, N2O and other condensibles are first removed by a series of traps at liquid nitrogen temperature. CO is then quantitatively oxidized to CO2 by the Sofonocat reagent and subsequently removed by further cryotraps. CH4 is then combusted to CO2 by passing the air through a 800°C furnace containing platinized quartz wool. The CH4-derived CO2 is then captured. This CO2 is then converted to graphite over ultra-high-purity iron powder and subsequently measured for 14C by AMS. The combined procedural 14CH4 blank for all steps of sampling handling was determined to be 0.75 ± 0.38 pMC, on the basis of 72 processed blank and standard samples (Petrenko et al., 2008b). For CO analyses, the sample handling is very similar except that the air bypasses Sofnocat, and the furnace temperature is reduced from 800 to 150°C. This allows for complete combustion of CO while CH4 passes through unaffected. CO2 derived from CO was diluted with 14-C free CO2 to increase the carbon mass to allow for a 14C measurement. For sample 14CO2 measurements, CO2 was extracted cryogenically from ~0.5 L of air. DATA COLLECTION AND PROCESSING The 14CH4 data are corrected the procedural blank. Where indicated, 14CH4 data are also corrected for cosmogenic 14C production in ice. For 14CO, corrections are applied for ambient air inclusion and processing blank. For 14CO2, processing blank corrections are applied where indicated. Sampling Location, Pakitsoq, Greenland: 69.43050°N, 50.25330°W, 350m DATA: The tables below contain data from a study that performed measurements of 14CH4 on large-volume samples of glacial ice from an ice margin site called Pakitsoq in West Greenland. As-measured data, as well as data corrected for cosmogenic 14CH4 production in ice are shown. The amount of cosmogenic 14CH4 was estimated based on measurements of cosmogenic 14CO in the samples (Table 2) Maximum expected 14CH4 values are based on sample age and the assumption that 14C of CH4 is equal to 14C of contemporaneous atmospheric CO2. 1. Table 1 Sample Mean gas age, yr BP Max.PossAirAgeRange 14CH4 measured,pMC MaxExpect14CH4 CH4ppb ExpectedCH4ppb 14CH4corr.For14C Corrected 14CH4, age-corrected Younger Dryas 1 11637 ± 75 11560 - 11739 35.42 ± 1.21 28.52 524.1 ± 1.85 519.92 ± 11.1 28.64 ± 1.23 170.4 ± 50.3 Younger Dryas 2 11631 ± 73 11551 - 11739 35.1 ± 1.19 28.57 527.16 ± 1.58 519.92 ± 11.1 28.45 ± 1.21 161.8 ± 49.2 YD-PB Transition 1 11480 ± 15 11416 - 11587 34.4 ± 1.05 28.7 659.1 ± 2.1 670.07 ± 20.28 28.28 ± 1.07 134.1 ± 43 YD-PB Transition 2 11470 ± 15 11418 - 11559 33.72 ± 1.04 28.74 678.62 ± 2.43 687.23 ± 19.46 28.96 ± 1.05 159.8 ± 42 Preboreal 1 11364 ± 109 11293 - 11416 32.11 ± 1 28.86 768.49 ± 2.03 757.04 ± 12.14 26.1 ± 1.02 32.1 ± 40.4 Preboreal 2 11354 ± 132 11312 - 11435 33.66 ± 1.03 28.94 760.26 ± 2.61 748.09 ± 12.1 28.16 ± 1.05 112.2 ± 41.6 2. Table 2 Variations in the total methane source (Qtotal) and the fossil fraction of the methane source (Qfossil) during the Younger Dryas - Preboreal transition as derived from 14CH4 data Periods compared ChangeQtot ChangeQfossil Q=0YD QChangeQfossil; assume Qfossil = 45 Tg/y for YD Younger Dryas (141 Tg/yr) -> YD-PB Trans. +43 -7 - +11 -5 - +13 Younger Dryas -> Preboreal +63 +6 - +23 +16 - +34 3. Table 3 C-14 of CO measured in Pakitsoq large-volume ancient air samples. Modeled cosmogenic 14CO is based on estimates of cosmic ray intensities at the Pakitsoq site and production rates of 14C by neutrons and muons with depth. Sample [COppb Meas14CO,diluted Inferred14COundil. Determined14COcosmo Modeled14COcosmo, molecules per g ice Younger Dryas 1 671 71.8 ± 1.0 394.9 ± 23.5 2.1 - 7.5 9.5 Younger Dryas 2 584 49.1 ± 0.6 444.6 ± 28.3 0.0 - 4.9 9.4 YD-PB Transition 1 636 78.7 ± 0.6 431.2 ± 25.1 3.0 - 7.8 10.7 YD-PB Transition 2 736 69.3 ± 1.1 381.5 ± 22.9 2.3 - 7.2 8.6 Preboreal 1 567 83.4 ± 0.9 477.2 ± 28.4 3.5 - 8.1 12.3 Preboreal 2 879 71.7 ± 0.7 367.9 ± 21.2 2.8 - 8.9 11.2 4. Table 4 Measurements of CO2 and 14CO2 in Pakitsoq large-volume air samples "Blank CO2…" and "Modern CO2…" are synthetic samples used to assess the procedural blank from CO2 extractions from air at SIO "SIO modern …" and "SIO dead …" are aliquots of pure CO2 from tanks that were used to make up the "Modern CO2…" and "Blank CO2 …" samples Sample MeasCO2air 14CO2,pMC,corrANSTO 14CO2,pMCcorrSIO Expected14CO2,pMC,based on sample age Younger Dryas 1 110 68.45 ± 0.63 71.18 ± 2.75 28.52 Younger Dryas 2 131 71.69 ± 0.75 74.04 ± 2.33 28.57 YD - PB Transition 163 71.95 ± 0.98 73.85 ± 2.71 28.63 YD - PB Transition 209 72.35 ± 0.77 73.85 ± 2.14 28.68 Preboreal 1 155 65.47 ± 0.67 67.30 ± 2.53 28.86 Preboreal 2 215 75.85 ± 0.72 77.36 ± 2.15 28.94 Blank CO2 mix #1 -0.04 ± 0.20 Modern CO2 mix #1 105.16 ± 1.34 Modern CO2 mix #2 103.71 ± 1.45 Blank CO2 mix #2 0.16 ± 0.22 SIO modern CO2 106.71 ± 1.19 SIO modern CO2 107.64 ± 1.20 SIO dead CO2 0.13 ± 0.14 SIO dead CO2 0.11 ± 0.15