GRIP Oxygen-18 of Atmospheric Oxygen

REFERENCES:

Leuenberger, M.C. 1997. Modeling of the signal transfer of seawater d18O to
the d18O of atmospheric oxygen using a diagnostic box model for the
terrestrial and marine biosphere. Journal of Geophysical Research 102:26841
26850.

Sowers, T., E.J. Brook, D. Etheridge, T. Blunier, A. Fuchs, M.C.
Leuenberger, J.A. Chappellaz, J.M. Barnola, M. Wahlen, B. Deck, and C.
Weyhenmeyer. 1997. An interlaboratory comparison of techniques for
extracting and analyzing trapped gases in ice cores. Journal of Geophysical
Research 102:26527-26538.

Fuchs, A., and M.C. Leuenberger. 1996. d18O of atmospheric oxygen measured
on the GRIP ice core document stratagraphic disturbances in the lowest 10%
of the core. Geophysical Research Letters 9:1049-1052.

DATA DESCRIPTION:

The file contains two columns:
Column 1: Depth (meters below the surface)
Column 2: d18O values (permil against modern air taken at Bern in 1994). 

The measurements presented here have been performed in Bern using a dry
extraction technique developed by Moor and Stauffer, (1984) and at LMCE
with a wet extraction (Sowers et al., 1989). The extracted air samples are
analyzed for isotopic oxygen content on a MAT 250 (Bern) and a MAT 252
(LMCE), respectively. The results are given as permil deviations from the
isotopic composition of modern atmospheric oxygen (air 1994). As part of
the inter-laboratory comparison of techniques for extracting and analyzing
trapped gases in ice cores, we have compared the scales used by Bender and
Sowers and the Bern group (Sowers et al., 1996). The overall analytical
precisions are similar in both labs and amount to 0.13o/oo in Bern and
0.15o/oo at LMCE for the gravitation corrected values, which are given
here. The gravitation correction has been made using measured d15N2 values
of the corresponding samples. 
 
d18O measured on oxygen in the bubble air from ice cores is a proxy for
continental ice volume and is used to synchronize cores from Greenland and
Antarctica (Bender et al., 1985, Sowers et al., 1993). A record measured
on ice samples from the Central Greenland deep ice core GRIP, spanning the
Last Glacial Maximum and the Holocene, shows that d18O of atmospheric
oxygen is in good agreement with measurements on the Vostok, Byrd and
GISP2 ice cores (Bender et al., 1994, Sowers and Bender, 1995). The smooth
isotope record of atmospheric oxygen represents a steady ice sheet decay
within the time resolution of about 2000 to 3000 years for atmospheric
oxygen. 

The Emian records as shown here documents the potential of d18O
measurements for tracing stratigraphic disturbances. Measurements
performed on ice from the GRIP core older than 100 kyrs (about 2700 mbs)
do not correlate with the corresponding Vostok record and show transitions
too fast to be typical for ice sheet build-up or decay. Furthermore, the
expected time lag between d18Oatm and d18O of seawater or d18O of ice is
absent or has even turned into a lead. Climatic interpretation of the fast
d18Oice transitions is not consistent with our d18Oatm results. By
combining our d18Oatm record with the methane (CH4) record at the same
depth levels and by comparing them to their Antarctic counterpart from
Vostok, we constrain the possible age of the ice in the disturbed region.
The combination suggests that the layers with heavy d18Oice correspond
indeed to ice from the last Interglacial (stage 5e) whereas layers with
light d18Oice correspond to ice either from stage 5d or from the
penultimate glaciation, mechanically inserted into the ice from stage 5e. 

DATA:	

Depth (m)	del18O
Midpoint	(per mil)

987.25	0.01
1069.2	-0.08
1182.5	-0.29
1219.35	-0.18
1319.45	-0.37
1343.1	-0.19
1400.85	-0.19
1431.1	-0.2
1491.6	0.04
1546.6	0.14
1590.6	0.33
1651.1	0.61
1717.1	0.83
1761.1	1.07
1816.65	0.95
1860.1	0.93
1893.1	0.95
1937.65	0.85
1952.5	0.79
1970.1	0.87
1999.8	0.76
2058.65	0.59
2124.65	0.4
2157.65	0.44
2190.1	0.46
2201.65	0.56
2267.1	0.44
2319.9	0.46
2390.3	0.28
2762.65	0.67
2770.35	0.95
2778.6	0.67
2789.6	0.43
2807.2	0.69
2811.6	0.1
2811.6	-0.12
2827	0.6
2830.3	0.63
2835.25	0.82
2835.8	0.77
2840.2	-0.33
2842.95	-0.07
2855.6	-0.11
2868.25	0.34
2871.55	0.29
2880.9	0.28
2883.65	1.07
2884.2	0.94
2885.85	0.86
2891.9	1.04
2901.25	1.02
2908.4	0.18
2910.6	0.04
2915.55	0.45
2933.7	0.34
2949.1	0.35