# NEEM-2011-S1 Ice Core 1800 Year Continuous Methane Data #----------------------------------------------------------------------- # World Data Center for Paleoclimatology, Boulder # and # NOAA Paleoclimatology Program #----------------------------------------------------------------------- # NOTE: Please cite original reference when using these data, # plus the Online Resource and date accessed. # # Online_Resource: http://hurricane.ncdc.noaa.gov/pls/paleox/f?p=519:1:::::P1_STUDY_ID:14173 # # Original_Source_URL: ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/neem/neem2011s1-ch4-5yr.txt # # Description/Documentation lines begin with # # Data lines have no # # # Archive: Ice Cores #-------------------- # Contribution_Date # Date: 2013-04-04 #-------------------- # Title # Study_Name: NEEM-2011-S1 Ice Core 1800 Year Continuous Methane Data #-------------------- # Investigators # Investigators: Rhodes, R.H.; Faïn, X.; Stowasser, C.; Blunier, T.; Chappellaz, J.; McConnell, J.R.; Romanini, D.; Mitchell, L.E.; Brook, E.J. #-------------------- # Description_and_Notes # Description: Methane concentration from the Greenland NEEM-2011-S1 Ice Core from 71 to 408m depth (~270-1961AD). # Methane concentrations analysed online by laser spectrometer (SARA, Spectroscopy by Amplified Resonant Absorption, # developed at Laboratoire Interdisciplinaire de Physique, Grenoble, France) on gas extracted from an ice core # processed using a continuous melter system (Desert Research Institute). Methane data have a 5 second integration time # (raw data acquisition rate 0.6 Hz). Analytical precision, from Allan Variance test, is 0.9 ppb (2 sigma). # Long-term reproducibility is 2.6% (2 sigma). Gaps in the record are due to problems during online analysis. # Online analysis conducted August-September 2011. # Note: Lat-Long provided is for main NEEM borehole. The NEEM-2011-S1 core was drilled 200 m distance away in 2011 to 410 m depth. # # Four data series are presented, as follows: # 1: neem2011s1-ch4.txt = entire dataset # 2: neem2011s1-ch4-outliers-removed.txt = Data minus data points exceeding cut-off value. # Cut-off value is 2*median absolute deviation (MAD)> 15 yr running median. # Different MAD values used for 250-1000 AD and 1100-1835 AD sections of record. # 3: neem2011s1-ch4-outliers.txt = Data points removed from dataset according to specified cut-off value. # Please refer to Rhodes et al. (2013) for full discussion of origins outlying data points. # Briefly, these high frequency features are not artifacts of the continuous method # and have been replicated by traditional discrete analyses. Comparison to chemistry # measurements suggests they are related to biological in situ production of methane. # 4: neem2011s1-ch4-5yr.txt = Median CH4 concentrations for 5 year time slices of Data_outliers_removed. # This can be utilised as a time series of atmospheric methane concentration because the # influence of outliers and other high frequency features (that could not survive firn # smoothing processes (see Spahni et al., 2003) is removed. # # Methane concentrations are reported on NOAA2004 scale (instrument calibrated on dry synthetic air standards). # # A correction factor of 1.079 has been applied to all data to correct for methane dissolution in melted ice core sample # prior to gas extraction. Correction factor calculated using empirical data (concentrations not aligned/tied to existing # discrete methane measurements). # # Additional methods description provided in: # Stowasser, C., Buizert, C., Gkinis, V., Chappellaz, J., Schupbach, S., Bigler, M., Fain, X., Sperlich, P., Baumgartner, M., # Schilt, A., Blunier, T., 2012. Continuous measurements of methane mixing ratios from ice cores. Atmos. Meas. Tech. 5, 999-1013. # # Morville, J., Kassi, S., Chenevier, M., Romanini, D., 2005. # Fast, low-noise, mode bymode, cavity-enhanced absorption spectroscopy by diode-laser self-locking. Appl. Phys. B Lasers Opt. 80, 1027-01038. # # NEEM (North Greenland Eemian Ice Drilling) project information http://neem.dk/ # #-------------------- # Publication # Authors: Rachael H. Rhodes, Xavier Faïn, Christopher Stowasser, Thomas Blunier, Jérôme Chappellaz, Joseph R. McConnell, Daniele Romanini, Logan E. Mitchell, Edward J. Brook # Published_Date_or_Year: 2013-04-15 # Published_Title: Continuous methane measurements from a late Holocene Greenland ice core: Atmospheric and in-situ signals # Journal_Name: Earth and Planetary Science Letters # Volume: 368 # Issue: # Pages: 9-19 # DOI: 10.1016/j.epsl.2013.02.034 # Abstract: Ancient air trapped inside bubbles in ice cores can now be analysed for methane concentration utilising a laser spectrometer coupled to a continuous melter system. We present a new ultra-high resolution record of atmospheric methane variability over the last 1800 yr obtained from continuous analysis of a shallow ice core from the North Greenland Eemian project (NEEM-2011-S1) during a 4-week laboratory-based measurement campaign. Our record faithfully replicates the form and amplitudes of multi-decadal oscillations previously observed in other ice cores and demonstrates the detailed depth resolution (5.3 cm), rapid acquisition time (30 m day-1) and good long-term reproducibility (2.6%, 2sigma) of the continuous measurement technique. In addition, we report the detection of high frequency ice core methane signals of non-atmospheric origin. Firstly, measurements of air from the firn-ice transition region and an interval of ice core dating from 1546-1560 AD (gas age) resolve apparently quasi-annual scale methane oscillations. Traditional gas chromatography measurements on discrete ice samples confirm these signals and indicate peak-to-peak amplitudes of ca. 22 parts per billion (ppb). We hypothesise that these oscillations result from staggered bubble close-off between seasonal layers of contrasting density during time periods of sustained multi-year atmospheric methane change. Secondly, we report the detection of abrupt (20-100 cm depth interval), high amplitude (35-80 ppb excess) methane spikes in the NEEM ice that are reproduced by discrete measurements. We show for the first time that methane spikes present in thin and infrequent layers in polar, glacial ice are accompanied by elevated concentrations of carbon- and nitrogen-based chemical impurities, and suggest that biological in-situ production may be responsible. #------------------ # Funding_Agency # Funding_Agency_Name: US National Science Foundation # Grant: 0944552, 0909541, 0968391 #------------------ # Funding_Agency # Funding_Agency_Name: ANR France # Grant: ANR-10-RPDOC-002-01, ANR-07-VULN-09-001 #------------------ # Funding_Agency # Funding_Agency_Name: European Research Council # Grant: FP7/2007-2013 Grant Agreement 291062 #------------------ # Site_Information # Site_Name: NEEM # Location: North America>Greenland # Country: # Northernmost_Latitude: 77.451 # Southernmost_Latitude: 77.451 # Easternmost_Longitude: -51.061 # Westernmost_Longitude: -51.061 # Elevation: 2450 m #------------------ # Data_Collection # Collection_Name: NEEM-2011-S1-CH4-5yr # Earliest_Year: 273 # Most_Recent_Year: 1942 # Time_Unit: AD # Core_Length: 408 m # Notes: #------------------ # Chronology: # # Gas age scale constructed from annual-layer-counted ice age (Sigl et al., # in press, Journal of Geophysical Research, doi:10.1029/2012JD018603) # and constant delta age of 190.1 yr. Time span of record is 270-1961 AD. # #---------------- # Variables # # Data variables follow (have no #) # Data line variables format: Variables list, one per line, shortname-tab-longname-tab-longname components (9 components: what, material, error, units, seasonality, archive, detail, method, C or N for Character or Numeric data) # ## age_AD age, , , AD, , , , ,N ## ch4_ppb CH4 concentration, , , ppb, , , , ,N # #---------------- # Data: # Data lines follow (have no #) # Data line format - tab-delimited text, variable short name as header # Missing Values: age_AD ch4_ppb 273 712.3 278 702.75 283 705.6 287 693.4 292 699.35 300 690.9 305 689.5 310 694.35 315 693.9 320 693.35 325 693.6 330 694.7 335 697 339 693.3 352 689.5 358 687.6 363 679.8 366 682.15 373 682.2 378 676.9 381 675.45 391 672.35 395 671.7 403 681.1 407 682.6 411 677.8 417 681.3 422 687.6 429 689.15 434 691.85 439 688.3 444 681.6 449 680.8 453 679.2 458 678.35 516 669.5 520 675.25 527 676.8 532 678.75 537 682.95 542 684.6 547 682.7 551 693.2 559 698.4 564 697.9 568 691.2 574 691.5 581 695 586 692.2 590 685.8 596 684.1 603 684.2 610 682.45 615 682.6 620 679.3 623 680.4 634 683.8 638 686.8 645 691.3 652 687.2 654 686.35 662 683.4 667 680.2 672 683.05 677 683.3 681 689.7 688 695.1 694 694.4 702 688.8 708 691.7 711 709.75 737 700.1 745 688 751 679.9 756 684.1 761 680.7 766 675 770 673.8 777 673.1 782 674.2 786 674.9 791 672.45 796 684.35 801 689.6 806 689.2 816 689.2 821 696.75 826 690.2 834 686 840 685.3 845 696.2 850 694.8 855 700.2 859 698.45 865 701.1 869 697.1 875 694.1 879 693.7 885 695.2 895 702.8 901 715.3 905 703.5 910 698.8 914 697.6 931 700.5 936 704.75 941 706.3 946 708.2 949 710.1 961 713.2 966 710.7 972 717.6 976 714.4 982 717.4 986 713.05 991 720 995 725 1000 725 1122 736.4 1127 739.55 1132 743.65 1137 744.6 1142 748.45 1146 749.4 1152 747.4 1157 749.3 1161 741.85 1167 742.6 1172 742.9 1177 744 1182 740.5 1186 740.3 1194 734.4 1199 737.8 1232 723.45 1236 726.5 1241 725.4 1246 725.2 1251 727.4 1256 726.35 1261 730.1 1265 734.5 1274 726.35 1279 731.25 1284 731 1289 734.9 1294 736.8 1300 740.4 1305 742.1 1310 735.8 1315 735.45 1319 729.3 1325 728.6 1330 725.8 1335 727.3 1340 728.3 1344 728.7 1350 724.6 1354 731.05 1361 733.35 1366 733.6 1371 734.8 1376 732.2 1381 730.4 1386 730.2 1393 726.1 1399 721.3 1405 719.4 1410 723.35 1415 725.1 1420 728.3 1424 729.6 1431 722.8 1436 726.7 1440 725.9 1445 726.7 1450 727 1456 727.55 1459 727.35 1469 728.9 1474 735.5 1479 739.5 1484 739.35 1488 752.4 1495 748.3 1499 753.4 1506 759.5 1511 760.95 1516 762.7 1521 763.85 1526 769.5 1531 772.1 1537 768.65 1541 768.3 1546 762.1 1551 759.9 1556 744.9 1561 738.1 1566 733.9 1571 730 1576 729.9 1581 730.3 1586 729 1591 729.4 1595 735.7 1617 739.2 1622 736.6 1627 735.7 1632 735 1637 739.5 1642 731.8 1647 736.4 1652 740 1655 741.35 1661 742 1699 730.1 1704 733.55 1709 737.35 1714 739.7 1719 741.9 1724 744.3 1729 747.3 1734 756.3 1741 753.4 1746 761.9 1751 760.05 1756 767.1 1761 769.7 1767 776 1771 776.6 1777 783.2 1782 782.5 1787 782.65 1792 786.35 1797 789 1802 794.5 1807 801.1 1812 809.95 1817 819.15 1822 824.8 1827 829.2 1833 833.85 1835 837.2 1868 889.9 1873 897.3 1878 909.95 1887 944.9 1892 966.55 1897 982.2 1902 1008.5 1907 1040.85 1912 1061.9 1917 1080.85 1922 1112 1927 1125.5 1932 1149.7 1937 1172.15 1942 1235.4