Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide

M. O. Battle, J. P. Severinghaus, E. D. Sofen, D. Plotkin, A. J. Orsi, M. Aydin, S. A. Montzka, T. Sowers, P. P. Tans

Research output: Contribution to journalArticle

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Abstract

We sampled interstitial air from the perennial snowpack (firn) at a site near the West Antarctic Ice Sheet Divide (WAIS-D) and analyzed the air samples for a wide variety of gas species and their isotopes. We find limited convective influence (1.4-5.2 m, depending on detection method) in the shallow firn, gravitational enrichment of heavy species throughout the diffusive column in general agreement with theoretical expectations, a ∼10 m thick lock-in zone beginning at ∼67 m, and a total firn thickness consistent with predictions of Kaspers et al. (2004). Our modeling work shows that the air has an age spread (spectral width) of 4.8 yr for CO2 at the firn-ice transition. We also find that advection of firn air due to the 22 cm yr-1 ice-equivalent accumulation rate has a minor impact on firn air composition, causing changes that are comparable to other modeling uncertainties and intrinsic sample variability. Furthermore, estimates of Δage (the gas age/ice age difference) at WAIS-D appear to be largely unaffected by bubble closure above the lock-in zone. Within the lock-in zone, small gas species and their isotopes show evidence of size-dependent fractionation due to permeation through the ice lattice with a size threshold of 0.36 nm, as at other sites. We also see an unequivocal and unprecedented signal of oxygen isotope fractionation within the lock-in zone, which we interpret as the mass-dependent expression of a size-dependent fractionation process.

Original languageEnglish (US)
Pages (from-to)11007-11021
Number of pages15
JournalAtmospheric Chemistry and Physics
Volume11
Issue number21
DOIs
StatePublished - Nov 14 2011

Fingerprint

firn
ice sheet
air
fractionation
ice
gas
isotope
snowpack
detection method
accumulation rate
modeling
oxygen isotope
bubble
advection
Pleistocene
prediction

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Cite this

Battle, M. O., Severinghaus, J. P., Sofen, E. D., Plotkin, D., Orsi, A. J., Aydin, M., ... Tans, P. P. (2011). Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide. Atmospheric Chemistry and Physics, 11(21), 11007-11021. https://doi.org/10.5194/acp-11-11007-2011
Battle, M. O. ; Severinghaus, J. P. ; Sofen, E. D. ; Plotkin, D. ; Orsi, A. J. ; Aydin, M. ; Montzka, S. A. ; Sowers, T. ; Tans, P. P. / Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide. In: Atmospheric Chemistry and Physics. 2011 ; Vol. 11, No. 21. pp. 11007-11021.
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Battle, MO, Severinghaus, JP, Sofen, ED, Plotkin, D, Orsi, AJ, Aydin, M, Montzka, SA, Sowers, T & Tans, PP 2011, 'Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide', Atmospheric Chemistry and Physics, vol. 11, no. 21, pp. 11007-11021. https://doi.org/10.5194/acp-11-11007-2011

Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide. / Battle, M. O.; Severinghaus, J. P.; Sofen, E. D.; Plotkin, D.; Orsi, A. J.; Aydin, M.; Montzka, S. A.; Sowers, T.; Tans, P. P.

In: Atmospheric Chemistry and Physics, Vol. 11, No. 21, 14.11.2011, p. 11007-11021.

Research output: Contribution to journalArticle

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T1 - Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide

AU - Battle, M. O.

AU - Severinghaus, J. P.

AU - Sofen, E. D.

AU - Plotkin, D.

AU - Orsi, A. J.

AU - Aydin, M.

AU - Montzka, S. A.

AU - Sowers, T.

AU - Tans, P. P.

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Y1 - 2011/11/14

N2 - We sampled interstitial air from the perennial snowpack (firn) at a site near the West Antarctic Ice Sheet Divide (WAIS-D) and analyzed the air samples for a wide variety of gas species and their isotopes. We find limited convective influence (1.4-5.2 m, depending on detection method) in the shallow firn, gravitational enrichment of heavy species throughout the diffusive column in general agreement with theoretical expectations, a ∼10 m thick lock-in zone beginning at ∼67 m, and a total firn thickness consistent with predictions of Kaspers et al. (2004). Our modeling work shows that the air has an age spread (spectral width) of 4.8 yr for CO2 at the firn-ice transition. We also find that advection of firn air due to the 22 cm yr-1 ice-equivalent accumulation rate has a minor impact on firn air composition, causing changes that are comparable to other modeling uncertainties and intrinsic sample variability. Furthermore, estimates of Δage (the gas age/ice age difference) at WAIS-D appear to be largely unaffected by bubble closure above the lock-in zone. Within the lock-in zone, small gas species and their isotopes show evidence of size-dependent fractionation due to permeation through the ice lattice with a size threshold of 0.36 nm, as at other sites. We also see an unequivocal and unprecedented signal of oxygen isotope fractionation within the lock-in zone, which we interpret as the mass-dependent expression of a size-dependent fractionation process.

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