期刊
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES
卷 120, 期 6, 页码 2558-2574出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/2014JD022766
关键词
firn; layering; ice core; methane; firn density; total air content
资金
- NSF OPP [0538578, 0520523, 0538538, 0944343, 0944078, 1142166, 1043528]
- NASA/Oregon Space Grant Consortium [NNG05GJ85H]
- NOAA Climate and Global Change Fellowship Program
- Polar Academic Program (PAP) of Korea Polar Research Institute (KOPRI) [PD12010]
- NSF [ANT-0944018, ANT-1245663, 0230396, 0440817, 0944348, 0944266]
- NSF OPP
- Directorate For Geosciences
- Office of Polar Programs (OPP) [0944552, 1142166] Funding Source: National Science Foundation
- Directorate For Geosciences
- Office of Polar Programs (OPP) [1043528] Funding Source: National Science Foundation
- Office Of The Director
- Office Of Internatl Science &Engineering [0968391] Funding Source: National Science Foundation
- Ministry of Land, Transport & Maritime Affairs (MOLIT), South Korea [PD12010] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
Interpretation of ice core trace gas records depends on an accurate understanding of the processes that smooth the atmospheric signal in the firn. Much work has been done to understand the processes affecting air transport in the open pores of the firn, but a paucity of data from air trapped in bubbles in the firn-ice transition region has limited the ability to constrain the effect of bubble closure processes. Here we present high-resolution measurements of firn density, methane concentrations, nitrogen isotopes, and total air content that show layering in the firn-ice transition region at the West Antarctic Ice Sheet (WAIS) Divide ice core site. Using the notion that bubble trapping is a stochastic process, we derive a new parameterization for closed porosity that incorporates the effects of layering in a steady state firn modeling approach. We include the process of bubble trapping into an open-porosity firn air transport model and obtain a good fit to the firn core data. We find that layering broadens the depth range over which bubbles are trapped, widens the modeled gas age distribution of air in closed bubbles, reduces the mean gas age of air in closed bubbles, and introduces stratigraphic irregularities in the gas age scale that have a peak-to-peak variability of 10 years at WAIS Divide. For a more complete understanding of gas occlusion and its impact on ice core records, we suggest that this experiment be repeated at sites climatically different from WAIS Divide, for example, on the East Antarctic plateau.
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