GISP2 Ice Core 32KYr in-situ 14C Data --------------------------------------------------------------------- NOAA Paleoclimatology Program and World Data Center for Paleoclimatology, Boulder --------------------------------------------------------------------- NOTE: PLEASE CITE ORIGINAL REFERENCE WHEN USING THIS DATA!!!!! NAME OF DATA SET: GISP2 Ice Core 32KYr in-situ 14C Data LAST UPDATE: 6/2005 (Original Receipt by WDC Paleo) CONTRIBUTOR: Devendra Lal, Scripps Institution of Oceanography IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2005-043 SUGGESTED DATA CITATION: Lal, D., et al., 2005. GISP2 Ice Core 32KYr in-situ 14C Data, IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series #2005-043. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA. ORIGINAL REFERENCE: Lal, D., A.J.T. Jull, D. Pollard, and L. Vacher. 2005. Evidence for large century time-scale changes in solar activity in the past 32 Kyr, based on in-situ cosmogenic 14C in ice at Summit, Greenland. Earth and Planetary Science Letters 234, pp. 335-349. ABSTRACT: We present results of estimates of cosmic ray flux in Greenland at the Summit (3200 m.a.s.l, 72.68N, 38.58W), during the past 32 Kyr. We derive these estimates based on concentrations of in-situ cosmogenic 14C produced in ice crystals. Based on the secular equilibrium concentration of in-situ produced 14C in quartz in terrestrial rocks, we find that on century time-scales, the cosmic ray production rate of 14C at the Summit was close to its estimated long-term average production rate, except during 3 periods: (i) during 8500–9500 yr B.P. and 27,000–32,000 yr B.P, when the production rate was higher by about a factor of 2, and (ii) during 12,000–16,000 yr B.P, when the production rate was lower by a factor of ~1.5. The observed variation in cosmic ray flux at the polar site is best attributed to changes in solar activity resulting in variable modulation of terrestrial cosmic ray flux. Changes in the geomagnetic field in the past do not affect the cosmic ray flux at polar latitudes. Likewise, climate changes do not affect the in-situ 14C record in ice. During the first two epochs, the solar activity must have been very low, as during Maunder Minimum (virtually no sunspots), resulting in essentially no modulation of the cosmic ray flux by the solar plasma. During the low cosmic ray flux epoch, 12,000–16,000 yr B.P., the observed decrease in cosmic ray flux corresponds to high solar activity as seen in 1958 (sunspot number ~190). We discuss the proxy evidence from tree ring and sediment based records of atmospheric 14C/12C ratios during the three epochs. These records have been used as a measure of changes in cosmic ray flux, and solar activity in the past. However, since they are also appreciably affected by climatic changes, a comparison of the two records is potentially valuable for delineating the nature of past changes in solar activity, and large-scale ocean circulation and air–sea exchange. ADDITIONAL REFERENCES: D. Lal, A.J.T. Jull, G.S. Burr, and D.J. Donahue. 2000. On the characteristics of cosmogenic in-situ 14C in documented GISP2 Holocene ice samples. Nucl. Instrum. Methods Phys. Res., B 172 pp. 623–631. D.A. Meese, A.J. Gow, R.B. Alley, G.A. Zielinski, P.M. Grootes, M. Ram, K.C. Taylor, P.A. Mayewski, and J.F. Bolzon. 1997. The Greenland ice sheet project 2 depth-age scale: methods and results. J. Geophys. Res. 102, pp. 26411– 26422. GEOGRAPHIC REGION: Greenland PERIOD OF RECORD: 32 KYrBP - present DESCRIPTION: The data give concentrations of in-situ cosmogenic 14C produced in ice crystals in GISP2 ice from the Summit (3200 m.a.s.l, 72.60 N, 38.50 W), during the past 32 Kyr. DATA: Table 1. Measured net 14C concentrations in GISP2 ice samples, corrected for radioactive decay and secondary 14C produced after extraction from the site, the corresponding relative cosmic ray fluxes during accumulation of the sample, and the observed partitioning of 14C activity in the 14CO and 14CO2 phases. For details of the experimental procedures, reference is made to Lal et al. 2000. Sample Mean depth Age a* Accumulation Net 14C conc. Relative cosmic Ratio, Code (m) (KyrBP) rate(cm/y)b* (atoms/g) c* ray flux 14CO/(14CO+14CO2) 126 125.75 375 25.75 1387 +/- 85 1.02 +/- 0.06 0.08 +/- 0.04 127 126.15 375 21.4 1281 +/- 114 0.79 +/- 0.07 0.07 +/- 0.05 251 250.25 1060 23.1 1658 +/- 80 1.10 +/- 0.05 0.20 +/- 0.03 751 751.5 3650 24.02 2281 +/- 122 1.57 +/- 0.08 0.34 +/- 0.04 1400-1 1400.3 8560 26.15 2693 +/- 181 2.02 +/- 0.14 0.29 +/- 0.05 1400-2 1400.85 8560 29.3 2848 +/- 164 2.39 +/- 0.14 0.36 +/- 0.04 1519 1518.5 9470 21.1 4789 +/- 238 2.90 +/- 0.14 0.75 +/- 0.11 1521-2 1520.85 9700 20.3 3221 +/- 292 1.87 +/- 0.17 0.45 +/- 0.09 1624 1623.5 10770 16.2 2643 +/- 276 1.23 +/- 0.13 0.33 +/- 0.07 1699 1698.5 12390 9.2 2475 +/- 334 0.65 +/- 0.09 0.02 +/- 0.80 1750 1749.4 13750 10.2 3036 +/- 432 0.89 +/- 0.13 0.26 +/- 0.10 O14 1821.5 15570 7.55 2671 +/- 589 0.58 +/- 0.13 0.35 +/- 0.12 1837 1837.4 16200 9.9 5131 +/- 635 1.46 +/- 0.18 0.39 +/- 0.10 DG9 1836 20650 7.15 4910 +/- 929 1.01 +/- 0.19 0.33 +/- 0.02 DG2 2005.5 24550 6.25 5537 +/- 1104 0.99 +/- 0.20 0.40 +/- 0.03 DG5 2051 27650 7.05 9637 +/- 2252 1.95 +/- 0.46 0.68 +/- 0.03 DG6 2096 30350 7.05 9857 +/- 2446 1.99 +/- 0.49 0.44 +/- 0.03 O12 2101 30650 7.35 10779 +/- 2749 2.27 +/- 0.58 0.28 +/- 0.07 DG1 2110 31250 7.45 8791 +/- 2566 1.88 +/- 0.55 0.37 +/- 0.04 a* The ice ages are based on Meese et al. 1997. b* The accumulation rates are based on observed ice thicknesses, and the ice accumulation model for the 200 km retreat of the ice sheet margin. c* Net 14C concentrations are the values corrected for radioactive decay and secondary 14C formed in the samples after they were extracted from the site. They should be considered as the values in the ice samples at the time when the in-situ 14C was formed by cosmic ray interactions in individual layers.