GISP2 Ice Core 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 in situ 14C Data LAST UPDATE: 9/2003 (Original Receipt by WDC Paleo) CONTRIBUTOR: D. Lal, Scripps Institution of Oceanography IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2003-064 SUGGESTED DATA CITATION: Lal, D., et al., 2003, GISP2 Ice Core in situ 14C Data, IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series #2003-064. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA. ORIGINAL REFERENCES: Lal, D., A.J.T. Jull, G.S. Burr, and D.J. Donahue, 2000, On the characteristics of cosmogenic in situ 14C in some GISP2 Holocene and late glacial ice samples, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 172, Issues 1-4, October 2000, Pages 623-631. doi: 10.1016/S0168-583X(00)00275-5. Lal, D., A.J.T. Jull, G.S. Burr, and D.J. Donahue. 1997. Measurements of in situ 14C concentrations in Greenland Ice Sheet Project 2 ice covering a 17 kyr time span: Implications to ice flow dynamics. Journal of Geophysical Research 102:26505-26510. GEOGRAPHIC REGION: Greenland PERIOD OF RECORD: 16 KYrBP - present ABSTRACT: In previous studies, we have shown that information on ice accumulation processes is recorded by the in situ production of 14C, from nuclear interactions of cosmic rays with oxygen in ice (Lal et al., 1997). In this report, we discuss a study of a number of Holocene and several glacial ice samples from the GISP2 core whose accumulation rates are known and which should be little affected by uncertainties in ice flow models (Cuffey et al., 1997), to determine trapping efficiencies of in situ 14C. We present new results along with discussion of the earlier results of Lal et al. (1997), which include results on partitioning of in situ 14C among the CO and CO2 phases through time in ice. The usefulness of the in situ 14C data to measurements of ice accumulation rates and ages are discussed. DESCRIPTION: in situ 14C data from the GISP2 Ice Core. DATA: Tables 1-3 from Lal et al. 2000. Space-delimited ASCII text - best viewed with fixed width font such as courier. Table 1. Measurements of 14C concentration in GISP2 ice in the upper and lower halves of core, 1400-1401 m(a) Sample Code Depth Range (m) Weight (kg) Measured 14C concentration (atoms/g)* CO-phase CO2-phase GISP2-1400-1 (01) 1400.0-1400.6 1.8 340 ± 35 900 ± 40 2nd Extraction (01R) 1400.0-1400.6 1.8 ~0 ± 30 80 ± 30 GISP2-1400-2 (05) 1400.6-1401.0 1.61 340 ± 30 800 ± 40 2nd Extraction (05R) 1400.6-1401.0 1.61 68 ± 25 140 ± 30 (a)For age and trapped 14C corrected net in-situ concentrations of 14C in these samples, see Table 4. *Concentration values are corrected for line blanks of 14CO and 14CO2 (see text). Table 2. Measured 14C concentrations in GISP2 Holocene ice samples, based on two extractions(*), without correction for decay, and trapped 14C. Sample Code Depth Range(m) Weight(kg) Age(yr) AirVol Measured 14C conc.(atoms/g)(**) (ccSTP/g) CO-phase CO2-phase GISP2-126 125.5-126.0 1.5 375 77.9 115±70 1860±50 GISP2-127 126.0-126.3 0.98 ~375 136.5 95±70 1780±60 GISP2-251 250-250.5 1.51 1060 74.7 315±50 1810±560 GISP2-751 751-752 1.4 3650 71.9 930±60 1440±60 GISP2-1400-1 1400-1400.6 1.8 8560 72.6 340±35 980±50 GISP2-1400-2 1400.6-1401 1.61 8560 73.8 410±40 940±50 GISP2-1521-U 1520-1520.6 2.2 9700 82.2 130±50 530±35 GISP2-1521-L 1520.6-1521.0 1.7 9700 82 490±90 825±50 GISP2-1624 1623.0-1624.0 2.5 10,770 76.7 255±50 690±50 GISP2-1699 1698.0-1699.0 2.8 12,390 77.9 10±70 960±70 GISP2-1750 1749.0-1749.8 2.7 13,750 86.1 170±60 620±60 GISP2-1837.0 1837.0-1837.8 2.8 16,200 80.9 315±70 570±70 (*)For details of extraction procedures, see Lal et al. [9]. (**)For net 14C concentrations in CO and CO2 phases, corrected for trapped 14C and radioactive decay of 14C, see Table 3. Table 3 In-situ concentrations of 14CO and 14CO2 in GISP2 ice, and estimated accumulation rates Sample Code Depth Range(m) Net 14C Net 14C Tot.in-situ Net** in-situ Ratio 14CO/ Accum.rate Accum.rate(cm/y) (atoms/g)* (atoms/g)* 14C(atoms/g) 14C(atoms/g) (14CO+14CO2)*** Based on Based on CO-phase CO2-phase In-situ 14C flow model**** GISP2-126 125.5-126.0 120±70 1340±50 1460±90 1390±85 (0.08±0.04) 25.2±1.6 25.75±9.8 GISP2-127 126.0-126.3 100±70 1250±60 1350±120 1280±110 (0.07±0.05) 27.2±2.4 21.4±6.9 GISP2-251 250-250.5 360±55 1400±640 1760±640 1660±80 0.20±0.03 21.0±1.0 23.1±6.3 GISP2-751 751-752 825±90 1600±90 2430±130 2280±120 0.34±0.04 15.3±0.8 24.0±5.1 GISP2-1400-1 1400-1400.6 860±135 2120±145 2980±200 2700±180 0.29±0.05 13.0±0.9 26.1±9.3 GISP2-1400-2 1400.6-1401 1140±110 1990±140 3135±180 2850±160 0.36±0.04 12.3±0.7 29.3±8.2 GISP-2-1519 1518.0-1519.0 3860±180 1270±180 5130±255 4790±240 0.75±0.11 7.29±0.4 22.3±2.3 GISP2-1521-U 1520-1520.6 380±180 980±110 1360±210 1050±160 0.28±0.14 33.2±5.1 21.1±4.1 GISP2-1521-L 1520.6-1521.0 1590±280 1940±150 3530±320 3220±290 0.45±0.0.09 10.8±1.0 20.3±2.2 GISP2-1624 1623.0-1624.0 940±190 1930±190 2870±300 2640±280 0.33±0.07 13.2±1.4 16.2±7.9 GISP2-1699 1698.0-1699.0 50±250 2910±250 2960±400 2470±330 (0.02±0.08) 14.1±1.9 9.2±4.0 GISP2-1750 1749.0-1749.8 915±325 2595±320 3510±500 3035±430 0.26±0.10 11.5±1.6 10.2±4.3 GISP2-1837.0 1837.0-1837.8 2235±470 3425±470 5660±700 5130±630 0.39±0.10 6.8±0.8 9.9±3.9 (*)Corrected for radioactive decay of 14C, and trapped 14C, based on measured air volumes and CO2 concentrations[11]. (**)Corrected for secondary 14C produced at the coring site and at the Denver storage site. (***)Ratios within parentheses have large statistical errors. (****)The range of values are based on model calculations of Cuffey and Clow[10] of thinning factors, for a 200 km retreat of the ice sheet margin following the last glacial maximum, considered to be most realistic (Cuffey, priv. comm.). We thank K.M. Cuffey for providing us with layer-wise depth accumulation data corresponding to different ice dynamics scenarios (see also [20]).