TITLE: 14C measurements in large-volume ice samples from Pakitsoq, West Greenland PI: Jeffrey Severinghaus Scripps Institution of Oceanography Mail Code 0244 Univ. California San Diego 9500 Gilman Dr. La Jolla, CA 92093, USA +1 858 822 2483 jseveringhaus@ucsd.edu Contact for data questions: Vasilii Petrenko Department of Earth and Environmental Sciences University of Rochester Rochester, NY 14627 USA +1 585 276 6094 vpetrenk@z.rochester.edu FUNDING: NSF OPP Award 0221470 DATA SET OVERVIEW 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 results have been published in Petrenko et al. (2009). The ice samples were collected between Jul 1 and Aug 15, 2005. The sampling site coordinates are: N 69.43050˚,W 50.25330˚ 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. DATA FORMAT Excel file with multiple tables. Most column headings are self explanatory. Some clarifications: Table 2: "Change in Qtotal" is as in Brook et al, 2000. Two extreme-end scenarios for the fossil component of the methane budget were assumed for the Younger Dryas: 0 Tg/yr and 45 Tg/yr. Table 3: Modeled cosmogenic 14CO is based on published production rates as in van der Kemp et al. (2002) and Lal et al. (1987). DATA REMARKS None REFERENCES: Brook, E.J., S. Harder, J. Severinghaus, E. J. Steig, 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., Nishiizumi, K., Arnold, J.R. (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., Smith, A. M., Brook, E. J., Lowe, D., Riedel, K., Brailsford, G., Hua, Q., Schaefer, H., Reeh, N., Weiss, R. F., Etheridge, D., and Severinghaus, J. P. (2009). (CH4)-C-14 Measurements in Greenland Ice: Investigating Last Glacial Termination CH4 Sources. Science 324, 506-508. Petrenko, V. V., Severinghaus, J. P., Brook, E. J., Mühle, J., Headly, M., Harth, C., Schaefer, H., Reeh, N., Weiss, R., Lowe, D. C., and Smith, A. M. (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., Smith, A. M., Brailsford, G., Riedel, K., Hua, Q., Lowe, D., Severinghaus, J. P., Levchenko, V., Bromley, T., Moss, R., Muhle, J., and Brook, E. J. (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., Alderliesten, C., Van Der Borg, K., De Jong, A., Lamers, R. Oerlemans, J., Thomassen, M., Van De Wal, R. (2002). In situ produced C-14 by cosmic ray muons in ablating Antarctic ice. Tellus B 54, 186-192.