The influence of layering and barometric pumping on firn air transport in a 2D model
Abstract. Ancient air trapped in ice core bubbles has been paramount to developing our understanding of past climate and atmospheric composition. Before air bubbles become isolated in ice, the atmospheric signal is altered in the firn column by transport processes such as advection and diffusion. Ho...
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ftcdlib:oai:escholarship.org:ark:/13030/qt84f589k6 2024-09-15T18:11:58+00:00 The influence of layering and barometric pumping on firn air transport in a 2D model Birner, Benjamin Buizert, Christo Wagner, Till JW Severinghaus, Jeffrey P 2017-12-19 application/pdf https://escholarship.org/uc/item/84f589k6 https://escholarship.org/content/qt84f589k6/qt84f589k6.pdf https://doi.org/10.5194/tc-2017-233 unknown eScholarship, University of California qt84f589k6 https://escholarship.org/uc/item/84f589k6 https://escholarship.org/content/qt84f589k6/qt84f589k6.pdf doi:10.5194/tc-2017-233 public article 2017 ftcdlib https://doi.org/10.5194/tc-2017-233 2024-06-28T06:28:19Z Abstract. Ancient air trapped in ice core bubbles has been paramount to developing our understanding of past climate and atmospheric composition. Before air bubbles become isolated in ice, the atmospheric signal is altered in the firn column by transport processes such as advection and diffusion. However, the influence of impermeable layers and barometric pumping (driven by surface pressure variability) on firn air transport is not well understood and cannot be captured in conventional 1-dimensional firn air models. Here we present a 2-dimensional (2D) trace gas advection-diffusion-dispersion model that accounts for discontinuous horizontal layers of reduced permeability. We find that layering and barometric pumping individually yield too small a reduction in gravitational settling to match observations. In contrast, a combination of both effects more strongly suppresses gravitational fractionation. Layering locally focuses airflows in the 2D model and thus amplifies the dispersive mixing resulting from barometric pumping. Hence, the representation of both factors is needed to obtain a more natural emergence of the lock-in zone. Moreover, we find that barometric pumping in the layered 2D model does not substantially change the differential kinetic fractionation of fast and slow diffusing trace gases, which is observed in nature. This suggests that further subgrid-scale physics may be missing in the current generation of firn air transport models. However, we find robust scaling relationships between kinetic isotope fractionation of different noble gas isotope and elemental ratios. These relationships may be used to correct for kinetic fractionation in future high precision ice core studies. Article in Journal/Newspaper ice core University of California: eScholarship |
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University of California: eScholarship |
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Abstract. Ancient air trapped in ice core bubbles has been paramount to developing our understanding of past climate and atmospheric composition. Before air bubbles become isolated in ice, the atmospheric signal is altered in the firn column by transport processes such as advection and diffusion. However, the influence of impermeable layers and barometric pumping (driven by surface pressure variability) on firn air transport is not well understood and cannot be captured in conventional 1-dimensional firn air models. Here we present a 2-dimensional (2D) trace gas advection-diffusion-dispersion model that accounts for discontinuous horizontal layers of reduced permeability. We find that layering and barometric pumping individually yield too small a reduction in gravitational settling to match observations. In contrast, a combination of both effects more strongly suppresses gravitational fractionation. Layering locally focuses airflows in the 2D model and thus amplifies the dispersive mixing resulting from barometric pumping. Hence, the representation of both factors is needed to obtain a more natural emergence of the lock-in zone. Moreover, we find that barometric pumping in the layered 2D model does not substantially change the differential kinetic fractionation of fast and slow diffusing trace gases, which is observed in nature. This suggests that further subgrid-scale physics may be missing in the current generation of firn air transport models. However, we find robust scaling relationships between kinetic isotope fractionation of different noble gas isotope and elemental ratios. These relationships may be used to correct for kinetic fractionation in future high precision ice core studies. |
format |
Article in Journal/Newspaper |
author |
Birner, Benjamin Buizert, Christo Wagner, Till JW Severinghaus, Jeffrey P |
spellingShingle |
Birner, Benjamin Buizert, Christo Wagner, Till JW Severinghaus, Jeffrey P The influence of layering and barometric pumping on firn air transport in a 2D model |
author_facet |
Birner, Benjamin Buizert, Christo Wagner, Till JW Severinghaus, Jeffrey P |
author_sort |
Birner, Benjamin |
title |
The influence of layering and barometric pumping on firn air transport in a 2D model |
title_short |
The influence of layering and barometric pumping on firn air transport in a 2D model |
title_full |
The influence of layering and barometric pumping on firn air transport in a 2D model |
title_fullStr |
The influence of layering and barometric pumping on firn air transport in a 2D model |
title_full_unstemmed |
The influence of layering and barometric pumping on firn air transport in a 2D model |
title_sort |
influence of layering and barometric pumping on firn air transport in a 2d model |
publisher |
eScholarship, University of California |
publishDate |
2017 |
url |
https://escholarship.org/uc/item/84f589k6 https://escholarship.org/content/qt84f589k6/qt84f589k6.pdf https://doi.org/10.5194/tc-2017-233 |
genre |
ice core |
genre_facet |
ice core |
op_relation |
qt84f589k6 https://escholarship.org/uc/item/84f589k6 https://escholarship.org/content/qt84f589k6/qt84f589k6.pdf doi:10.5194/tc-2017-233 |
op_rights |
public |
op_doi |
https://doi.org/10.5194/tc-2017-233 |
_version_ |
1810449556260782080 |