Pakitsoq Greenland Ice Methane Carbon Isotope Data ----------------------------------------------------------------------- World Data Center for Paleoclimatology, Boulder and NOAA Paleoclimatology Program ----------------------------------------------------------------------- NOTE: PLEASE CITE CONTRIBUTORS WHEN USING THIS DATA!!!!! NAME OF DATA SET: Pakitsoq Greenland Ice Methane Carbon Isotope Data LAST UPDATE: 8/2006 (Original receipt by WDC Paleo) CONTRIBUTOR: Hinrich Schaefer, University of Victoria and Oregon State University. IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2006-083 SUGGESTED DATA CITATION: Schaefer, H., et al. 2006. Pakitsoq Greenland Ice Methane Carbon Isotope Data. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series # 2006-083. NOAA/NCDC Paleoclimatology Program, Boulder CO, USA. ORIGINAL REFERENCE: Schaefer, H., M.J. Whiticar, E.J. Brook, V.V. Petrenko, D.F. Ferretti, and J.P. Severinghaus. 2006. Ice Record of d13C for Atmospheric CH4 Across the Younger Dryas–Preboreal Transition. Science, Vol. 313, pp. 1109-1112, 10.1126/science.1126562, 25 August 2006. ABSTRACT: We report atmospheric methane carbon isotope ratios (d13CH4) from the Western Greenland ice margin spanning the Younger Dryas-to-Preboreal (YD-PB) transition. Over the recorded ~800 years, d13CH4 was around -46 per mil; that is, ~1 per mil higher than in the modern atmosphere and ~5.5 per mil higher than would be expected from budgets without 13C-rich anthropogenic emissions. This requires higher natural 13C-rich emissions or stronger sink fractionation than conventionally assumed. Constant d13CH4 during the rise in methane concentration at the YD-PB transition is consistent with additional emissions from tropical wetlands, or aerobic plant CH4 production, or with a multisource scenario. A marine clathrate source is unlikely. ADDITIONAL REFERENCES: Petrenko, V. V., J.P. Severinghaus, E.J. Brook, N. Reeh, and H. Schaefer. 2006. Gas records from the West Greenland ice margin covering the Last Glacial Termination: a horizontal ice core. Quaternary Science Reviews, Vol. 25, Issues 9-10, pp. 865-875, May 2006. Schaefer H. 2005. Stable Carbon Isotopic Composition of Methane from Ancient Ice Samples. Thesis, pp.191, University of Victoria. GEOGRAPHIC REGION: Western Greenland PERIOD OF RECORD: Younger Dryas–Preboreal Transition, 12.2 - 11.3 KyrBP FUNDING SOURCES: The project was supported by a German Academic Exchange Service (DAAD) fellowship (H.S.), a Canadian Centre for Climate Modeling and Analysis Environment Canada grant (M.J.W.), a Natural Sciences and Engineering Research Council Discovery Grant (M.J.W.), Canadian Foundation for Climate and Atmospheric Sciences Project Grant GR-417 (M.J.W.), and NSF grants OPP-0221410 (E.J.B.) and OPP-0221470 (J.P.S.). DESCRIPTION: d13CH4 in air dating between 11,360 and 12,220 years before the present was measured in ice samples from the Pakitsoq outcrop (Western Greenland). The record covers the transition between the Younger Dryas (YD) and Preboreal Holocene (PB), when temperature and CH4 increased rapidly at the termination of the last ice age. A total of 82 ice samples from Pakitsoq were analyzed for d13CH4 of enclosed air. The estimated range in age per sample is ca. 25 - 35 yr, which includes both sample thickness and gas age distribution due to diffusion and bubble enclosure. For replicate measurements (multiple ice samples of equal age) we report mean values with standard errors. For single measurements we show analytical precision as derived from the standard ice measurements during that measurement period. Several kinds of visible post-depositional features in the ice, such as fractures, layers or occlusions of dust, as well as certain bubble free bands, were associated with anomalously high values for both [CH4] and d13CH4, compared to surrounding unaffected samples. 11 samples were rejected from the final data set for this reason. Pakitsoq age scale The gas age scale used for assigning dates according to location in the sample profile is derived by comparison of three geochemical records from Pakitsoq and GISP2. Start and end points of prominent fluctuations in d15N, CH4, and d18Oice observed in Pakitsoq were matched with corresponding events recorded in GISP2. The tie points are: (i) the start and peak of the end-of-YD d15N increase; (ii) the start and end of the Allerød – YD CH4 decline; (iii) the d18Oice minimum during the intra-Allerød cold period; and (iv) the d18Oice drop into the YD and rise into the PB. The corresponding ages of the GISP2 age scale were corrected by -80 yr to match the date of 11,570 yrBP for the end-of-YD event derived from tree ring ages and assigned to the Pakitsoq inflection points as fixed ages. Between these dates, which are apart by 500 yr at the most, age was interpolated linearly. DATA: Sampling campaign: identifies in which of three sampling campaigns any sample in this composite data set was collected. Trench location: the distance to an arbitrary reference point, comparable to the depth of an ice core sample. Age: as a function of distance in the Pakitsoq gas age scale, relative to 1950 A.D. (Schaefer et al. 2006). Methane concentration: calculated from GC-IRMS results (a/m = 42 peak size), sample size and air content. d13C uncorrected: the raw GC-IRMS data d15N correction: correction factor for gravitational and thermal fractionation derived by interpolation from Pakitsoq d15N data (Petrenko et al. 2006). Diffusion correction: correction factor for the effects of abrupt changes in atmospheric methane concentration derived from a firn diffusion model (Schaefer, 2005). d13C corrected: including d15N and diffusion correction. Sampling Trench Age Methane d13C d15N Diffusion d13C Standard campaign location concentrat. uncorr. correct. correct. correct. error (m) (kyr BP) (ppbV) (permil) (permil) (permil) (permil) (permil) Pak2001 1.29 12.222 457 -45.73 -0.38 0 -46.11 0.44 Pak2001 1.48 12.101 472 -46.50 -0.38 0 -46.88 0.44 Pak2001 1.57 12.044 443 -45.55 -0.39 0 -45.93 0.68 Pak2002 1.62 12.014 517 -45.25 -0.37 0 -45.62 0.37 Pak2002 1.64 12.000 473 -45.61 -0.37 0 -45.98 0.37 Pak2002 1.67 11.986 527 -45.42 -0.37 0 -45.79 0.37 Pak2002 1.71 11.960 461 -45.70 -0.38 0 -46.08 0.37 Pak2002 1.74 11.941 527 -45.49 -0.38 0 -45.87 0.05 Pak2002 1.83 11.859 583 -45.33 -0.39 0 -45.71 0.26 Pak2001 1.83 11.857 483 -44.79 -0.40 0 -45.19 0.44 Pak2002 1.94 11.763 527 -44.73 -0.42 0 -45.15 0.37 Pak2002 2.03 11.680 500 -45.39 -0.44 0 -45.83 0.37 Pak2003 2.05 11.660 639 -46.08 -0.40 0 -46.48 0.23 Pak2001 2.09 11.626 459 -45.76 -0.40 0 -46.16 0.44 Pak2003 2.12 11.597 565 -46.06 -0.42 0 -46.48 0.56 Pak2003 2.14 11.579 573 -46.36 -0.43 0 -46.79 0.20 Pak2003 2.17 11.562 596 -46.85 -0.45 0.30 -46.99 0.58 Pak2003 2.22 11.543 658 -47.20 -0.48 0.63 -47.04 0.27 Pak2003 2.24 11.535 712 -46.45 -0.49 0.69 -46.25 0.48 Pak2003 2.26 11.527 710 -45.02 -0.51 0.72 -44.81 1.52 Pak2002 2.28 11.520 622 -46.24 -0.52 0.74 -46.02 0.40 Pak2002 2.33 11.501 646 -46.55 -0.52 0.75 -46.32 0.37 Pak2003 2.34 11.495 730 -46.62 -0.54 0.75 -46.41 0.18 Pak2003 2.43 11.463 741 -46.07 -0.54 0.71 -45.90 0.39 Pak2002 2.45 11.459 717 -46.13 -0.53 0.70 -45.96 0.07 Pak2002 2.53 11.448 694 -45.76 -0.52 0.69 -45.59 0.37 Pak2003 2.54 11.446 837 -45.90 -0.53 0.69 -45.74 0.35 Pak2002 2.64 11.432 756 -45.16 -0.50 0.61 -45.05 0.51 Pak2001 2.64 11.431 733 -44.98 -0.52 0.60 -44.90 0.44 Pak2003 2.64 11.431 845 -45.30 -0.52 0.60 -45.22 0.48 Pak2002 2.64 11.431 706 -45.27 -0.50 0.60 -45.17 0.37 Pak2002 2.70 11.422 798 -45.19 -0.51 0.24 -45.46 0.37 Pak2003 2.74 11.417 784 -46.08 -0.51 0 -46.59 0.11 Pak2001 2.79 11.409 677 -46.76 -0.52 0 -47.28 0.44 Pak2003 2.83 11.403 844 -45.88 -0.52 0 -46.39 0.33 Pak2001 2.88 11.396 704 -42.65 -0.51 0 -43.16 0.44 Pak2003 2.93 11.388 810 -45.42 -0.52 0 -45.94 0.48 Pak2001 3.13 11.360 674 -44.62 -0.50 0 -45.12 0.72