HR: 1340h
AN: A53B-1167    [Abstracts]
TI: Firn-air Properties and Influences at the West Antarctic Ice Sheet Divide
AU: * Battle, M O
EM: mbattle@bowdoin.edu
AF: Bowdoin College, Dept. of Physics & Astronomy 8800 College Station, Brunswick, ME 04011-8488, United States
AU: Severinghaus, J P
EM: jseverin@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093-0230, United States
AU: Montzka, S A
EM: Stephen.A.Montzka@noaa.gov
AF: NOAA/ESRL, 325 Broadway, Boulder, CO 80305, United States
AU: Sofen, E D
EM: esofen@u.washington.edu
AF: Bowdoin College, Dept. of Physics & Astronomy 8800 College Station, Brunswick, ME 04011-8488, United States
AU: Sofen, E D
EM: esofen@u.washington.edu
AF: Now at University of Washington, Dept. of Atmospheric Sciences Box 351640, Seattle, WA 98195,
AU: Tans, P P
EM: Pieter.Tans@noaa.gov
AF: NOAA/ESRL, 325 Broadway, Boulder, CO 80305, United States
AB: In December 2005, we collected samples of firn air from a pair of dedicated boreholes drilled at the West Antarctic Ice Sheet Divide (WAIS-D), immediately adjacent to the WAIS-D deep ice coring effort currently underway at 79° 28'S, 112° 7'W at an elevation of ~1800m. The site is characterized by moderate temperatures (annual mean of -31°C) and moderate accumulation (24 cm/yr ice-equivalent). These samples were analyzed for a wide variety of atmospheric species by laboratories at the Scripps Institution of Oceanography, NOAA-ESRL, University of Colorado/INSTAAR, UC Irvine and Penn. State University. In this presentation, we focus on general properties of the firn air at this site and the influences on its composition, as inferred from concentration data for CO₂, CH₄, and a range of halogenated species, as well as the stable isotope ratios of N₂ and several noble gases. Preliminary analyses indicate the presence of a shallow convective zone (a few meters or less), a diffusive region extending down to roughly 65m and a lock-in zone from 65m to the firn-ice transition at 76.5m. There is also evidence of a thermally-driven seasonal cycle in composition in the upper 25m of the firn. Modeling studies indicate that the accumulation rate at this site is low enough that the downward advection of air accompanying firn compression has a very small influence on the firn air profile. Air at the bottom of the diffusive column has a CO₂-based age of 10-15 years (depending on the definition of "mean age"), while the air at the firn-ice transition is ~38 years old. Concentrations of halogenated species in the samples collected imply atmospheric histories that are generally consistent with those derived from direct atmospheric measurements and from firn air collected at other sites. Additional properties of the air, and their controlling processes will also be presented.
DE: 0365 Troposphere: composition and chemistry
DE: 0724 Ice cores (4932)
DE: 0798 Modeling
DE: 1610 Atmosphere (0315, 0325)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting