Critical porosity of gas enclosure in polar firn independent of climate
In order to interpret the paleoclimatic record stored in the air enclosed in polar ice cores, it is crucial to understand the fundamental lock-in process. Within the porous firn, bubbles are sealed continuously until the respective horizontal layer reaches a critical porosity. Present-day firn air m...
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ftcopernicus:oai:publications.copernicus.org:cp60340 2023-05-15T13:54:27+02:00 Critical porosity of gas enclosure in polar firn independent of climate Schaller, Christoph Florian Freitag, Johannes Eisen, Olaf 2018-09-27 application/pdf https://doi.org/10.5194/cp-13-1685-2017 https://cp.copernicus.org/articles/13/1685/2017/ eng eng doi:10.5194/cp-13-1685-2017 https://cp.copernicus.org/articles/13/1685/2017/ eISSN: 1814-9332 Text 2018 ftcopernicus https://doi.org/10.5194/cp-13-1685-2017 2020-07-20T16:23:32Z In order to interpret the paleoclimatic record stored in the air enclosed in polar ice cores, it is crucial to understand the fundamental lock-in process. Within the porous firn, bubbles are sealed continuously until the respective horizontal layer reaches a critical porosity. Present-day firn air models use a postulated temperature dependence of this value as the only parameter to adjust to the surrounding conditions of individual sites. However, no direct measurements of the firn microstructure could confirm these assumptions. Here we show that the critical porosity is a climate-independent constant by providing an extensive data set of micrometer-resolution 3-D X-ray computer tomographic measurements for ice cores representing different extremes of the temperature and accumulation ranges. We demonstrate why indirect measurements suggest a climatic dependence and substantiate our observations by applying percolation theory as a theoretical framework for bubble trapping. The incorporation of our results significantly influences the dating of trace gas records, changing gas-age–ice-age differences by up to more than 1000 years. This may further help resolve inconsistencies, such as differences between East Antarctic δ 15 N records (as a proxy for firn height) and model results. We expect our findings to be the basis for improved firn air and densification models, leading to lower dating uncertainties. The reduced coupling of proxies and surrounding conditions may allow for more sophisticated reinterpretations of trace gas records in terms of paleoclimatic changes and will benefit the development of new proxies, such as the air content as a marker of local insolation. Text Antarc* Antarctic Copernicus Publications: E-Journals Antarctic Climate of the Past 13 11 1685 1693 |
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Open Polar |
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Copernicus Publications: E-Journals |
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ftcopernicus |
language |
English |
description |
In order to interpret the paleoclimatic record stored in the air enclosed in polar ice cores, it is crucial to understand the fundamental lock-in process. Within the porous firn, bubbles are sealed continuously until the respective horizontal layer reaches a critical porosity. Present-day firn air models use a postulated temperature dependence of this value as the only parameter to adjust to the surrounding conditions of individual sites. However, no direct measurements of the firn microstructure could confirm these assumptions. Here we show that the critical porosity is a climate-independent constant by providing an extensive data set of micrometer-resolution 3-D X-ray computer tomographic measurements for ice cores representing different extremes of the temperature and accumulation ranges. We demonstrate why indirect measurements suggest a climatic dependence and substantiate our observations by applying percolation theory as a theoretical framework for bubble trapping. The incorporation of our results significantly influences the dating of trace gas records, changing gas-age–ice-age differences by up to more than 1000 years. This may further help resolve inconsistencies, such as differences between East Antarctic δ 15 N records (as a proxy for firn height) and model results. We expect our findings to be the basis for improved firn air and densification models, leading to lower dating uncertainties. The reduced coupling of proxies and surrounding conditions may allow for more sophisticated reinterpretations of trace gas records in terms of paleoclimatic changes and will benefit the development of new proxies, such as the air content as a marker of local insolation. |
format |
Text |
author |
Schaller, Christoph Florian Freitag, Johannes Eisen, Olaf |
spellingShingle |
Schaller, Christoph Florian Freitag, Johannes Eisen, Olaf Critical porosity of gas enclosure in polar firn independent of climate |
author_facet |
Schaller, Christoph Florian Freitag, Johannes Eisen, Olaf |
author_sort |
Schaller, Christoph Florian |
title |
Critical porosity of gas enclosure in polar firn independent of climate |
title_short |
Critical porosity of gas enclosure in polar firn independent of climate |
title_full |
Critical porosity of gas enclosure in polar firn independent of climate |
title_fullStr |
Critical porosity of gas enclosure in polar firn independent of climate |
title_full_unstemmed |
Critical porosity of gas enclosure in polar firn independent of climate |
title_sort |
critical porosity of gas enclosure in polar firn independent of climate |
publishDate |
2018 |
url |
https://doi.org/10.5194/cp-13-1685-2017 https://cp.copernicus.org/articles/13/1685/2017/ |
geographic |
Antarctic |
geographic_facet |
Antarctic |
genre |
Antarc* Antarctic |
genre_facet |
Antarc* Antarctic |
op_source |
eISSN: 1814-9332 |
op_relation |
doi:10.5194/cp-13-1685-2017 https://cp.copernicus.org/articles/13/1685/2017/ |
op_doi |
https://doi.org/10.5194/cp-13-1685-2017 |
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Climate of the Past |
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13 |
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11 |
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1685 |
op_container_end_page |
1693 |
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1766260314533265408 |