Dispersion in deep polar firn driven by synoptic-scale surface pressure variability

Other literature type, Article English OPEN
C. Buizert ; J. P. Severinghaus (2016)
  • Publisher: Copernicus Publications
  • Journal: The Cryosphere (issn: 1994-0416)
  • Related identifiers: doi: 10.5194/tc-10-2099-2016
  • Subject: GE1-350 | QE1-996.5 | Environmental sciences | Geology

Commonly, three mechanisms of firn air transport are distinguished: molecular diffusion, advection, and near-surface convective mixing. Here we identify and describe a fourth mechanism, namely dispersion driven by synoptic-scale surface pressure variability (or barometric pumping). We use published gas chromatography experiments on firn samples to derive the along-flow dispersivity of firn, and combine this dispersivity with a dynamical air pressure propagation model forced by surface air pressure time series to estimate the magnitude of dispersive mixing in the firn. We show that dispersion dominates mixing within the firn lock-in zone. Trace gas concentrations measured in firn air samples from various polar sites confirm that dispersive mixing occurs. Including dispersive mixing in a firn air transport model suggests that our theoretical estimates have the correct order of magnitude, yet may overestimate the true dispersion. We further show that strong barometric pumping, such as at the Law Dome site, may reduce the gravitational enrichment of <i>δ</i><sup>15</sup>N–N<sub>2</sub> and other tracers below gravitational equilibrium, questioning the traditional definition of the lock-in depth as the depth where <i>δ</i><sup>15</sup>N enrichment ceases. Last, we propose that <sup>86</sup>Kr excess may act as a proxy for past synoptic activity (or paleo-storminess) at the site.
  • References (64)
    64 references, page 1 of 7

    Adolph, A. C. and Albert, M. R.: Gas diffusivity and permeability through the firn column at Summit, Greenland: measurements and comparison to microstructural properties, The Cryosphere, 8, 319-328, doi:10.5194/tc-8-319-2014, 2014.

    Barnes, P. R. F., Wolff, E. W., and Mulvaney, R.: A 44 kyr paleoroughness record of the Antarctic surface, J. Geophys. Res.- Atmos., 111, D03102, doi:10.1029/2005JD006349, 2006.

    Battle, M., Bender, M., Sowers, T., Tans, P. P., Butler, J. H., Elkins, J. W., Ellis, J. T., Conway, T., Zhang, N., Lang, P., and Clarket, A. D.: Atmospheric gas concentrations over the past century measured in air from firn at the South Pole, Nature, 383, 231- 235, 1996.

    Battle, M. O., Severinghaus, J. P., Sofen, E. D., Plotkin, D., Orsi, A. J., Aydin, M., Montzka, S. A., Sowers, T., and Tans, P. P.: Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide, Atmos. Chem. Phys., 11, 11007- 11021, doi:10.5194/acp-11-11007-2011, 2011.

    Bay, R., Rohde, R., Price, P., and Bramall, N.: South Pole paleowind from automated synthesis of ice core records, J. Geophys. Res.- Atmos., 115, D14126, doi:10.1029/2009JD013741, 2010.

    Bendel, V., Ueltzhöffer, K. J., Freitag, J., Kipfstuhl, S., Kuhs, W. F., Garbe, C. S., and Faria, S. H.: High-resolution variations in size, number and arrangement of air bubbles in the EPICA DML (Antarctica) ice core, J. Glaciol., 59, 972-980, doi:10.3189/2013JoG12J245, 2013.

    Bender, M. L.: Orbital tuning chronology for the Vostok climate record supported by trapped gas composition, Earth Planet. Sc. Lett., 204, 275-289, doi:10.1016/S0012-821X(02)00980-9, 2002.

    Buizert, C.: ICE CORE METHODS/Studies of Firn Air, in: Encyclopedia of Quaternary Science (2nd Edn.), edited by: Elias, S. A. and Mock, C. J., 361-372, Elsevier, Amsterdam, doi:10.1016/B978-0-444-53643-3.00330-7, 2013.

    Buizert, C., Martinerie, P., Petrenko, V. V., Severinghaus, J. P., Trudinger, C. M., Witrant, E., Rosen, J. L., Orsi, A. J., Rubino, M., Etheridge, D. M., Steele, L. P., Hogan, C., Laube, J. C., Sturges, W. T., Levchenko, V. A., Smith, A. M., Levin, I., Conway, T. J., Dlugokencky, E. J., Lang, P. M., Kawamura, K., Jenk, T. M., White, J. W. C., Sowers, T., Schwander, J., and Blunier, T.: Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland, Atmos. Chem. Phys., 12, 4259-4277, doi:10.5194/acp-12-4259-2012, 2012.

    Buizert, C., Sowers, T., and Blunier, T.: Assessment of diffusive isotopic fractionation in polar firn, and application to ice core trace gas records, Earth Planet. Sc. Lett., 361, 110-119, doi:10.1016/j.epsl.2012.11.039, 2013.

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