Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements
We present elemental and isotopic measurements of noble gases (He, Ne, Ar, Kr, and Xe), oxygen and nitrogen of firn air from two sites. The first set of samples was taken in 1998 at the summit of the Devon Ice Cap in the eastern part of Devon Island. The second set was taken in 2001 at NGRIP locatio...
Published in: | Earth and Planetary Science Letters |
---|---|
Main Authors: | , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
Elsevier
2006
|
Subjects: | |
Online Access: | https://doi.org/10.1016/j.epsl.2005.12.036 |
id |
fteawag:oai:dora:eawag_5216 |
---|---|
record_format |
openpolar |
spelling |
fteawag:oai:dora:eawag_5216 2024-09-15T18:03:39+00:00 Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements Huber, C. Beyerle, U. Leuenberger, M. Schwander, J. Kipfer, R. Spahni, R. Severinghaus, J.P. Weiler, K. 2006 https://doi.org/10.1016/j.epsl.2005.12.036 eng eng Elsevier Earth and Planetary Sciences Letters--Earth Planet. Sci. Lett.--journals:732--0012-821X--1385-013X eawag:5216 journal id: journals:732 issn: 0012-821X e-issn: 1385-013X ut: 000236214500006 local: 10643 scopus: 2-s2.0-33344476457 doi:10.1016/j.epsl.2005.12.036 firn firn air firn-ice transition fractionation diffusion noble gases Text Journal Article 2006 fteawag https://doi.org/10.1016/j.epsl.2005.12.036 2024-08-05T03:04:29Z We present elemental and isotopic measurements of noble gases (He, Ne, Ar, Kr, and Xe), oxygen and nitrogen of firn air from two sites. The first set of samples was taken in 1998 at the summit of the Devon Ice Cap in the eastern part of Devon Island. The second set was taken in 2001 at NGRIP location (North Greenland). He and Ne are heavily enriched relative to Ar with respect to the atmosphere in the air near the close-off depth at around 50-70 m. The enrichment increases with depth and reaches the maximum value in the deepest samples just above the zone of impermeable ice where no free air could be extracted anymore. Similarly, elemental ratios of O 2 / N 2 , O 2 /Ar and Ar/N 2 are increasing with depth. In contrast but in line with expectations, isotopic ratios of 15 N/ 14 N, 18 O/ 16 O, and 36 Ar/ 40 Ar show no significant enrichment near the close-off depth. The observed isotopic ratios in the firn air column can be explained within the uncertainty ranges by the well-known processes of gravitational enrichment and thermal diffusion. To explain the elemental ratios, however, an additional fractionation process during bubble inclusion has to be considered. We implemented this additional process into our firn air model. The fractionation factors were found by fitting model profiles to the data. We found a very similar close-off fractionation behavior for the different molecules at both sites. For smaller gas species (mainly He and Ne) the fractionation factors are linearly correlated to the molecule size, whereas for diameters greater than about 3.6 Å the fractionation seems to be significantly smaller or even negligible. An explanation for this size dependent fractionation process could be gas diffusion through the ice lattice. At Devon Island the enrichment at the bottom of the firn air column is about four times higher compared to NGRIP. We explain this by lower firn diffusivity at Devon Island, most probably due to melt layers, resulting in significantly reduced back diffusion of the excess gas near the ... Article in Journal/Newspaper Devon Island Greenland Ice cap NGRIP North Greenland DORA Eawag Earth and Planetary Science Letters 243 1-2 61 73 |
institution |
Open Polar |
collection |
DORA Eawag |
op_collection_id |
fteawag |
language |
English |
topic |
firn firn air firn-ice transition fractionation diffusion noble gases |
spellingShingle |
firn firn air firn-ice transition fractionation diffusion noble gases Huber, C. Beyerle, U. Leuenberger, M. Schwander, J. Kipfer, R. Spahni, R. Severinghaus, J.P. Weiler, K. Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements |
topic_facet |
firn firn air firn-ice transition fractionation diffusion noble gases |
description |
We present elemental and isotopic measurements of noble gases (He, Ne, Ar, Kr, and Xe), oxygen and nitrogen of firn air from two sites. The first set of samples was taken in 1998 at the summit of the Devon Ice Cap in the eastern part of Devon Island. The second set was taken in 2001 at NGRIP location (North Greenland). He and Ne are heavily enriched relative to Ar with respect to the atmosphere in the air near the close-off depth at around 50-70 m. The enrichment increases with depth and reaches the maximum value in the deepest samples just above the zone of impermeable ice where no free air could be extracted anymore. Similarly, elemental ratios of O 2 / N 2 , O 2 /Ar and Ar/N 2 are increasing with depth. In contrast but in line with expectations, isotopic ratios of 15 N/ 14 N, 18 O/ 16 O, and 36 Ar/ 40 Ar show no significant enrichment near the close-off depth. The observed isotopic ratios in the firn air column can be explained within the uncertainty ranges by the well-known processes of gravitational enrichment and thermal diffusion. To explain the elemental ratios, however, an additional fractionation process during bubble inclusion has to be considered. We implemented this additional process into our firn air model. The fractionation factors were found by fitting model profiles to the data. We found a very similar close-off fractionation behavior for the different molecules at both sites. For smaller gas species (mainly He and Ne) the fractionation factors are linearly correlated to the molecule size, whereas for diameters greater than about 3.6 Å the fractionation seems to be significantly smaller or even negligible. An explanation for this size dependent fractionation process could be gas diffusion through the ice lattice. At Devon Island the enrichment at the bottom of the firn air column is about four times higher compared to NGRIP. We explain this by lower firn diffusivity at Devon Island, most probably due to melt layers, resulting in significantly reduced back diffusion of the excess gas near the ... |
format |
Article in Journal/Newspaper |
author |
Huber, C. Beyerle, U. Leuenberger, M. Schwander, J. Kipfer, R. Spahni, R. Severinghaus, J.P. Weiler, K. |
author_facet |
Huber, C. Beyerle, U. Leuenberger, M. Schwander, J. Kipfer, R. Spahni, R. Severinghaus, J.P. Weiler, K. |
author_sort |
Huber, C. |
title |
Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements |
title_short |
Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements |
title_full |
Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements |
title_fullStr |
Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements |
title_full_unstemmed |
Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements |
title_sort |
evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements |
publisher |
Elsevier |
publishDate |
2006 |
url |
https://doi.org/10.1016/j.epsl.2005.12.036 |
genre |
Devon Island Greenland Ice cap NGRIP North Greenland |
genre_facet |
Devon Island Greenland Ice cap NGRIP North Greenland |
op_relation |
Earth and Planetary Sciences Letters--Earth Planet. Sci. Lett.--journals:732--0012-821X--1385-013X eawag:5216 journal id: journals:732 issn: 0012-821X e-issn: 1385-013X ut: 000236214500006 local: 10643 scopus: 2-s2.0-33344476457 doi:10.1016/j.epsl.2005.12.036 |
op_doi |
https://doi.org/10.1016/j.epsl.2005.12.036 |
container_title |
Earth and Planetary Science Letters |
container_volume |
243 |
container_issue |
1-2 |
container_start_page |
61 |
op_container_end_page |
73 |
_version_ |
1810441127646461952 |