A sublimation technique for high-precision {_d63_1hn1_1hn3C [delta-13-C] on CO_1tn2 and CO_1tn2 mixing ratio from air trapped in deep ice cores [Elektronische Ressource] / Jochen Schmitt

Jschmitt

Informations

• Publié par: universitat_bremen
• Publié le: 01 janvier 2006
• Nombre de lectures: 22
• Langue: English
• Poids de l'ouvrage: 6 Mo

Extrait

A sublimation technique for
13high-precision δ C on CO and CO mixing ratio 2 2
from air trapped in deep ice cores



Jochen Schmitt



Dissertation zur Erlangung des Grades

Dr. rer. nat.





vorgelegt dem
Fachbereich Geowissenschaften
der Universität Bremen


Bremerhaven, Oktober 2006


Stiftung Alfred-Wegener-Institut für Polar- und Meeresforschung
in der Helmholtz-Gemeinschaft A sublimation technique for
13high-precision δ C on CO and CO mixing ratio 2 2
from air trapped in deep ice cores




















Gutachter:
Prof. Dr. Heinz Miller
Prof. Dr. Kai-Uwe Hinrichs


Stiftung Alfred-Wegener-Institut für Polar- und Meeresforschung
in der Helmholtz-Gemeinschaft

Contents

Zusammenfassung.........................................................................................................v
Thesis summary...........................................................................................................vii
1 Introduction............................................................................................................1
1.1 The global carbon cycle ............................................................................................... 3
1.2 Stable carbon isotopes and fractionation processes .................................................. 5
131.3 Reconstructing atmospheric δ C in the past............................................................. 8
132 Processes affecting δ C of the ice core gas archive..........................................16
2.1 Physical processes....................................................................................................... 16
2.1.1 Firn structure........................................................................................................ 17
2.1.2 Gas transport properties within the firn column................................................... 18
2.1.3 Enclosure process, age distribution and Δ-age..................................................... 19
2.1.4 Separation of gases and isotopes due to gravitation............................................. 21
2.1.5 Diffusion along a thermal gradient....................................................................... 22
2.1.6 Diffusion along a concentration gradient ............................................................. 23
2.1.7 Processes during bubble close-off........................................................................ 24
2.1.8 Clathrate formation and disintegration................................................................. 25
2.2 Chemical reactions and a possible in-situ production of CO ................................ 28 2
2.2.1 Indications for CO in-situ production from Greenland ice cores........................ 29 2
2.2.2 In-situ reactions of organic compounds ............................................................... 33
2.2.3 In-situ reactions of inorganic carbonate 38
132.3 Conclusions and requirements for the δ C analysis of ice cores........................... 40
132.3.1 δ C artifacts as a matter of scale ......................................................................... 41
2.3.2 Analytical requirements....................................................................................... 42 ii
133 Methods and instruments for δ C and CO analysis on ice cores ................. 43 2
3.1 Introduction................................................................................................................ 43
133.2 Previous approaches for δ C on ice cores using mechanical devices ................... 43
3.3 Quantitative extraction techniques for ice cores – sublimation in vacuum.......... 46
3.4 General layout of the entire method......................................................................... 49
3.5 The sublimation extraction system........................................................................... 53
3.5.1 Overall idea behind the sample trapping.............................................................. 53
3.5.2 Vacuum system and water removal ..................................................................... 56
3.5.3 Cooling system for compressed air...................................................................... 56
3.5.4 Sublimation vessel, internal water trap, and IR lamps......................................... 58
3.5.5 External water trap ............................................................................................... 59
3.5.6 CO trap and glass capillaries for CO storage .................................................... 62 2 2
3.5.7 Molesieve trap - air content measurement ........................................................... 63
3.5.8 Whole air reference inlet to introduce whole air standards.................................. 65
3.6 The tube cracker-GC-IRMS system (CF-IRMS) 67
3.6.1 Reasoning for a GC separation of the extracted gas sample................................ 68
3.6.2 General layout of the measurement sequence for the CF-IRMS system ............. 69
3.6.3 The tube cracker................................................................................................... 72
3.6.4 Device to introduce CO reference gas to the tube cracker ................................. 73 2
3.6.5 Humidifier for the He carrier (GC flow).............................................................. 74
3.6.6 Cryofocus and gas chromatographic separation of CO and N O ....................... 75 2 2
3.6.7 Open split and IRMS measurement ..................................................................... 77
3.7 Description on of the analysis procedure................................................................. 78
3.7.1 Sublimation extraction for ice core samples ........................................................ 78
3.7.2 Procedure to verify the analysis with air standards.............................................. 81
3.7.3 Tube cracker-GC-IRMS measurement scheme ................................................... 82
3.8 Raw data processing and performance of the CF-IRMS analysis......................... 83
133.8.1 δ C ...................................................................................................................... 84
3.8.2 CO concentration ................................................................................................ 87 2
iii
3.9 Results from air standard and blank measurements.............................................. 89
133.9.1 Reproducibility of δ C and overall accuracy for air standards ........................... 90
3.9.2 Reproducibility of the CO concentration for air standards................................. 92 2
3.9.3 Estimation of ‘side effects’ from air standards .................................................... 94
3.9.4 Procedural blanks................................................................................................. 97
4 Results and discussion of ice core measurements...........................................100
4.1 Ice core samples from the EDML ice core ............................................................. 100
4.2 Main characteristics of the measured ice core data .............................................. 102
4.3 Systematic differences during the sublimation extraction ................................... 103
4.4 Small-scale variability – differences among replicates ......................................... 108
4.5 Data comparison of the absolute values ................................................................. 110
4.5.1 Gravitational correction and ice core dating ...................................................... 110
4.5.2 Comparison with other Antarctic ice core records............................................. 112
4.6 Outlook...................................................................................................................... 117
References ..................................................................................................................119
5 Appendix: ...........................................................................................................129
Acknowledgements....................................................................................................165
Erklärung...................................................................................................................167








iv






Zusammenfassung

Das Eis der polaren Eisschilde stellt das einzige direkte Archiv dar, um Informationen über
die Zusammensetzung der Atmosphäre in der Vergangenheit zu erhalten. Bereits seit mehr als
10 Jahren weiß man durch Analyse von antarktischen Eiskernen, wie z.B. dem Vostok Eis-
kern, dass die Konzentration des Treibhausgases CO zwischen Eiszeiten und Warmzeiten 2
periodisch schwankte. Während der letzten vier Eiszeiten lag die CO Konzentration um etwa 2
90 ppmv niedriger als zu warmen Klimaperioden. Überraschend war die hohe Korrelation der
CO Konzentration mit der Temperatur. Mit Hilfe des Dome C Eiskerns, der im Rahmen des 2
europäischen