Kinetic fractionation of gases by deep air convection in polar firn

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dc.contributor.authorKawamura, K.
dc.contributor.authorSeveringhaus, J. P.
dc.contributor.authorAlbert, M. R.
dc.contributor.authorCourville, Z. R.
dc.contributor.authorFahnestock, M. A.
dc.contributor.authorScambos, T.
dc.contributor.authorShields, E.
dc.contributor.authorShuman, Christopher
dc.date.accessioned2022-02-15T13:55:37Z
dc.date.available2022-02-15T13:55:37Z
dc.date.issued2013-11-15
dc.description.abstractA previously unrecognized type of gas fractionation occurs in firn air columns subjected to intense convection. It is a form of kinetic fractionation that depends on the fact that different gases have different molecular diffusivities. Convective mixing continually disturbs diffusive equilibrium, and gases diffuse back toward diffusive equilibrium under the influence of gravity and thermal gradients. In near-surface firn where convection and diffusion compete as gas transport mechanisms, slow-diffusing gases such as krypton (Kr) and xenon (Xe) are more heavily impacted by convection than fast diffusing gases such as nitrogen (Nā‚‚) and argon (Ar), and the signals are preserved in deep firn and ice. We show a simple theory that predicts this kinetic effect, and the theory is confirmed by observations using a newly-developed Kr and Xe stable isotope system in air samples from the Megadunes field site on the East Antarctic plateau. Numerical simulations confirm the effect's magnitude at this site. A main purpose of this work is to support the development of a proxy indicator of past convection in firn, for use in ice-core gas records. To this aim, we also show with the simulations that the magnitude of the kinetic effect is fairly insensitive to the exact profile of convective strength, if the overall thickness of the convective zone is kept constant. These results suggest that it may be feasible to test for the existence of an extremely deep (~30ā€“40 m) convective zone, which has been hypothesized for glacial maxima, by future ice-core measurements.en_US
dc.description.sponsorshipMichael Bender made the nitrogen isotope measurements. Helpful discussions with Ralph Keeling, Bruce Cor nuelle, and Bill Young improved the manuscript. We thank the Megadunes Field Team and NY Air National Guard for field sup port, and the Light Ground Traverse 2003ā€“2004 for preparing the skiway that enabled LC-130 landings at the Megadunes site. Louise Albershardt of Ice Drilling and Design Operations group (IDDO) did the drilling. K. Kawamura acknowledges Fuyuki Saito of JAM STEC and Junā€™ichi Okuno of NIPR for assisting LaTeX editing. Support for this work came from NSF-OPP 02-30452 (J. P. Sever inghaus), Gary Comer Abrupt Climate Change Fellowship (for sup porting K. Kawamura as a postdoc at SIO) and JSPS KAKENHI 21671001 (K. Kawamura). The production of the paper was sup ported by an NIPR publication subsidy.en_US
dc.description.urihttps://acp.copernicus.org/articles/13/11141/2013/en_US
dc.format.extent15 pagesen_US
dc.genrejournal articlesen_US
dc.identifierdoi:10.13016/m2skhf-n2vv
dc.identifier.citationKawamura, K. et al. Kinetic fractionation of gases by deep air convection in polar firn. Atmos. Chem. Phys. 13 (2005), p 11141ā€“11155. https://doi.org/10.5194/acp-13-11141-2013.en_US
dc.identifier.urihttps://doi.org/10.5194/acp-13-11141-2013
dc.identifier.urihttp://hdl.handle.net/11603/24275
dc.language.isoen_USen_US
dc.publisherEGUen_US
dc.relation.isAvailableAtThe University of Maryland, Baltimore County (UMBC)
dc.relation.ispartofUMBC Joint Center for Earth Systems Technology
dc.relation.ispartofUMBC Faculty Collection
dc.rightsThis work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.en_US
dc.rightsPublic Domain Mark 1.0*
dc.rights.urihttp://creativecommons.org/publicdomain/mark/1.0/*
dc.titleKinetic fractionation of gases by deep air convection in polar firnen_US
dc.typeTexten_US
dcterms.creatorhttps://orcid.org/0000-0001-9606-767Xen_US

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