Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities
The transformation of snow into ice is a complex phenomenon that is difficult to model. Depending on surface temperature and accumulation rate, it may take several decades to millennia for air to be entrapped in ice. The air is thus always younger than the surrounding ice. The resulting gas–ice age...
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ftdoajarticles:oai:doaj.org/article:a80c897395c6442995dc92a3588cd805 2023-05-15T13:33:49+02:00 Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities C. Bréant P. Martinerie A. Orsi L. Arnaud A. Landais 2017-07-01T00:00:00Z https://doi.org/10.5194/cp-13-833-2017 https://doaj.org/article/a80c897395c6442995dc92a3588cd805 EN eng Copernicus Publications https://www.clim-past.net/13/833/2017/cp-13-833-2017.pdf https://doaj.org/toc/1814-9324 https://doaj.org/toc/1814-9332 doi:10.5194/cp-13-833-2017 1814-9324 1814-9332 https://doaj.org/article/a80c897395c6442995dc92a3588cd805 Climate of the Past, Vol 13, Pp 833-853 (2017) Environmental pollution TD172-193.5 Environmental protection TD169-171.8 Environmental sciences GE1-350 article 2017 ftdoajarticles https://doi.org/10.5194/cp-13-833-2017 2022-12-30T22:09:28Z The transformation of snow into ice is a complex phenomenon that is difficult to model. Depending on surface temperature and accumulation rate, it may take several decades to millennia for air to be entrapped in ice. The air is thus always younger than the surrounding ice. The resulting gas–ice age difference is essential to documenting the phasing between CO 2 and temperature changes, especially during deglaciations. The air trapping depth can be inferred in the past using a firn densification model, or using δ 15 N of air measured in ice cores. All firn densification models applied to deglaciations show a large disagreement with δ 15 N measurements at several sites in East Antarctica, predicting larger firn thickness during the Last Glacial Maximum, whereas δ 15 N suggests a reduced firn thickness compared to the Holocene. Here we present modifications of the LGGE firn densification model, which significantly reduce the model–data mismatch for the gas trapping depth evolution over the last deglaciation at the coldest sites in East Antarctica (Vostok, Dome C), while preserving the good agreement between measured and modelled modern firn density profiles. In particular, we introduce a dependency of the creep factor on temperature and impurities in the firn densification rate calculation. The temperature influence intends to reflect the dominance of different mechanisms for firn compaction at different temperatures. We show that both the new temperature parameterization and the influence of impurities contribute to the increased agreement between modelled and measured δ 15 N evolution during the last deglaciation at sites with low temperature and low accumulation rate, such as Dome C or Vostok. We find that a very low sensitivity of the densification rate to temperature has to be used in the coldest conditions. The inclusion of impurity effects improves the agreement between modelled and measured δ 15 N at cold East Antarctic sites during the last deglaciation, but deteriorates the agreement between modelled and ... Article in Journal/Newspaper Antarc* Antarctic Antarctica East Antarctica Directory of Open Access Journals: DOAJ Articles Antarctic East Antarctica Climate of the Past 13 7 833 853 |
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Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
Environmental pollution TD172-193.5 Environmental protection TD169-171.8 Environmental sciences GE1-350 |
spellingShingle |
Environmental pollution TD172-193.5 Environmental protection TD169-171.8 Environmental sciences GE1-350 C. Bréant P. Martinerie A. Orsi L. Arnaud A. Landais Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities |
topic_facet |
Environmental pollution TD172-193.5 Environmental protection TD169-171.8 Environmental sciences GE1-350 |
description |
The transformation of snow into ice is a complex phenomenon that is difficult to model. Depending on surface temperature and accumulation rate, it may take several decades to millennia for air to be entrapped in ice. The air is thus always younger than the surrounding ice. The resulting gas–ice age difference is essential to documenting the phasing between CO 2 and temperature changes, especially during deglaciations. The air trapping depth can be inferred in the past using a firn densification model, or using δ 15 N of air measured in ice cores. All firn densification models applied to deglaciations show a large disagreement with δ 15 N measurements at several sites in East Antarctica, predicting larger firn thickness during the Last Glacial Maximum, whereas δ 15 N suggests a reduced firn thickness compared to the Holocene. Here we present modifications of the LGGE firn densification model, which significantly reduce the model–data mismatch for the gas trapping depth evolution over the last deglaciation at the coldest sites in East Antarctica (Vostok, Dome C), while preserving the good agreement between measured and modelled modern firn density profiles. In particular, we introduce a dependency of the creep factor on temperature and impurities in the firn densification rate calculation. The temperature influence intends to reflect the dominance of different mechanisms for firn compaction at different temperatures. We show that both the new temperature parameterization and the influence of impurities contribute to the increased agreement between modelled and measured δ 15 N evolution during the last deglaciation at sites with low temperature and low accumulation rate, such as Dome C or Vostok. We find that a very low sensitivity of the densification rate to temperature has to be used in the coldest conditions. The inclusion of impurity effects improves the agreement between modelled and measured δ 15 N at cold East Antarctic sites during the last deglaciation, but deteriorates the agreement between modelled and ... |
format |
Article in Journal/Newspaper |
author |
C. Bréant P. Martinerie A. Orsi L. Arnaud A. Landais |
author_facet |
C. Bréant P. Martinerie A. Orsi L. Arnaud A. Landais |
author_sort |
C. Bréant |
title |
Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities |
title_short |
Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities |
title_full |
Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities |
title_fullStr |
Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities |
title_full_unstemmed |
Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities |
title_sort |
modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities |
publisher |
Copernicus Publications |
publishDate |
2017 |
url |
https://doi.org/10.5194/cp-13-833-2017 https://doaj.org/article/a80c897395c6442995dc92a3588cd805 |
geographic |
Antarctic East Antarctica |
geographic_facet |
Antarctic East Antarctica |
genre |
Antarc* Antarctic Antarctica East Antarctica |
genre_facet |
Antarc* Antarctic Antarctica East Antarctica |
op_source |
Climate of the Past, Vol 13, Pp 833-853 (2017) |
op_relation |
https://www.clim-past.net/13/833/2017/cp-13-833-2017.pdf https://doaj.org/toc/1814-9324 https://doaj.org/toc/1814-9332 doi:10.5194/cp-13-833-2017 1814-9324 1814-9332 https://doaj.org/article/a80c897395c6442995dc92a3588cd805 |
op_doi |
https://doi.org/10.5194/cp-13-833-2017 |
container_title |
Climate of the Past |
container_volume |
13 |
container_issue |
7 |
container_start_page |
833 |
op_container_end_page |
853 |
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1766046375445790720 |