The influence of layering and barometric pumping on firn air transport in a 2-D 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/qt1w171051 2023-11-05T03:36:23+01:00 The influence of layering and barometric pumping on firn air transport in a 2-D model Birner, Benjamin Buizert, Christo Wagner, Till JW Severinghaus, Jeffrey P 2021 - 2037 2018-01-01 application/pdf https://escholarship.org/uc/item/1w171051 unknown eScholarship, University of California qt1w171051 https://escholarship.org/uc/item/1w171051 public The Cryosphere, vol 12, iss 6 Earth Sciences Geology Oceanography Physical Geography and Environmental Geoscience Meteorology & Atmospheric Sciences article 2018 ftcdlib 2023-10-09T18:08:06Z 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 low-permeability layers and barometric pumping (driven by surface pressure variability) on firn air transport is not well understood and is not readily captured in conventional one-dimensional (1-D) firn air models. Here we present a two-dimensional (2-D) trace gas advection–diffusion–dispersion model that accounts for discontinuous horizontal layers of reduced permeability. We find that layering or barometric pumping individually yields too small a reduction in gravitational settling to match observations. In contrast, when both effects are active, the model's gravitational fractionation is suppressed as observed. Layering focuses airflows in certain regions in the 2-D model, which acts to amplify the dispersive mixing resulting from barometric pumping. Hence, the representation of both factors is needed to obtain a realistic emergence of the lock-in zone. In contrast to expectations, we find that the addition of barometric pumping in the layered 2-D model does not substantially change the differential kinetic fractionation of fast- and slow-diffusing trace gases. Like 1-D models, the 2-D model substantially underestimates the amount of differential kinetic fractionation seen in actual observations, suggesting that further subgrid-scale processes 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 and can amount to a bias of up to 0.45 °C in noble-gas-based mean ocean temperature reconstructions at WAIS Divide, Antarctica. Article in Journal/Newspaper Antarc* Antarctica ice core The Cryosphere University of California: eScholarship |
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Open Polar |
collection |
University of California: eScholarship |
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unknown |
topic |
Earth Sciences Geology Oceanography Physical Geography and Environmental Geoscience Meteorology & Atmospheric Sciences |
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Earth Sciences Geology Oceanography Physical Geography and Environmental Geoscience Meteorology & Atmospheric Sciences Birner, Benjamin Buizert, Christo Wagner, Till JW Severinghaus, Jeffrey P The influence of layering and barometric pumping on firn air transport in a 2-D model |
topic_facet |
Earth Sciences Geology Oceanography Physical Geography and Environmental Geoscience Meteorology & Atmospheric Sciences |
description |
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 low-permeability layers and barometric pumping (driven by surface pressure variability) on firn air transport is not well understood and is not readily captured in conventional one-dimensional (1-D) firn air models. Here we present a two-dimensional (2-D) trace gas advection–diffusion–dispersion model that accounts for discontinuous horizontal layers of reduced permeability. We find that layering or barometric pumping individually yields too small a reduction in gravitational settling to match observations. In contrast, when both effects are active, the model's gravitational fractionation is suppressed as observed. Layering focuses airflows in certain regions in the 2-D model, which acts to amplify the dispersive mixing resulting from barometric pumping. Hence, the representation of both factors is needed to obtain a realistic emergence of the lock-in zone. In contrast to expectations, we find that the addition of barometric pumping in the layered 2-D model does not substantially change the differential kinetic fractionation of fast- and slow-diffusing trace gases. Like 1-D models, the 2-D model substantially underestimates the amount of differential kinetic fractionation seen in actual observations, suggesting that further subgrid-scale processes 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 and can amount to a bias of up to 0.45 °C in noble-gas-based mean ocean temperature reconstructions at WAIS Divide, Antarctica. |
format |
Article in Journal/Newspaper |
author |
Birner, Benjamin Buizert, Christo Wagner, Till JW Severinghaus, Jeffrey P |
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 2-D model |
title_short |
The influence of layering and barometric pumping on firn air transport in a 2-D model |
title_full |
The influence of layering and barometric pumping on firn air transport in a 2-D model |
title_fullStr |
The influence of layering and barometric pumping on firn air transport in a 2-D model |
title_full_unstemmed |
The influence of layering and barometric pumping on firn air transport in a 2-D model |
title_sort |
influence of layering and barometric pumping on firn air transport in a 2-d model |
publisher |
eScholarship, University of California |
publishDate |
2018 |
url |
https://escholarship.org/uc/item/1w171051 |
op_coverage |
2021 - 2037 |
genre |
Antarc* Antarctica ice core The Cryosphere |
genre_facet |
Antarc* Antarctica ice core The Cryosphere |
op_source |
The Cryosphere, vol 12, iss 6 |
op_relation |
qt1w171051 https://escholarship.org/uc/item/1w171051 |
op_rights |
public |
_version_ |
1781691241881141248 |