HR: 1340h
AN: C33C-0356    [Abstracts]
TI: Close Resemblance Between Local Summer Insolation, O$_{2}$/N$_{2}$ and Total Air Content from the Dome Fuji Ice Core, Antarctica
AU: * Kawamura, K
EM: kkawamura@ucsd.edu
AF: Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University, Sendai, 980-8578 Japan
AU: * Kawamura, K
EM: kkawamura@ucsd.edu
AF: Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, Bern, 3012 Switzerland
AU: * Kawamura, K
EM: kkawamura@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0244 United States
AU: Nakazawa, T
EM: nakazawa@mail.tains.tohoku.ac.jp
AF: Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University, Sendai, 980-8578 Japan
AU: Aoki, S
EM: aoki@mail.tains.tohoku.ac.jp
AF: Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University, Sendai, 980-8578 Japan
AU: Fujii, Y
EM: fujii@pmg.nipr.ac.jp
AF: National Institute of Polar Research, 1-9-10 Kaga, Itabashi-ku, Tokyo, 173-8515 Japan
AU: Watanabe, O
EM: watanabe@nipr.ac.jp
AF: National Institute of Polar Research, 1-9-10 Kaga, Itabashi-ku, Tokyo, 173-8515 Japan
AU: Severinghaus, J P
EM: jseveringhaus@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0244 United States
AB: O$_{2}$/N$_{2}$ ratio from ice cores has shown depleted values compared to the atmosphere due to selective exclusion of O$_{2}$ during bubble formation at the base of firn. The long record from the Vostok ice core revealed that O$_{2}$/N$_{2}$ ratio records the local summer insolation. Insolation may affect physical properties of the firn near the surface, which later determines how much O$_{2}$/N$_{2}$ is fractionated the during bubble close-off process. We present here a supportive record of O$_{2}$/N$_{2}$ ratio for the last 340 kyr along the Dome Fuji ice core, Antarctica, which shows variations similar to the summer insolation at $77\deg$S. Moreover, the variation of total air content (TAC) in the Dome Fuji core resembles that of O$_{2}$/N$_{2}$. High TAC and high O$_{2}$/N$_{2}$ ratio appear at times of low summer insolation. Since the TAC variation is too large to be explained by the elevation change at the Dome Fuji site in the past, a possible cause is variation of the so-called ``lock-in zone'' thickness on the orders of several meters. The lock-in zone is a region 0-10 m thick at the bottom of firn where horizontal impermeable layers prevent vertical gas mixing. At times of low insolation, the firn would retain inhomogeneities such as wind crusts and high-density layers. These small-scale inhomogeneities do not affect bulk density very much but may help trap the gases at a lower bulk density (and higher porosity and thus TAC) through formation of a thicker lock-in zone than in times of high insolation. High insolation would homogenize the firn structure through recrystallization. O$_{2}$/N$_{2}$ ratio would be less depleted if there is a lock-in zone within the total close-off zone, because O$_{2}$ molecules once excluded from bubbles would eventually be re-trapped in the ice in the lock-in zone.
DE: 3344 Paleoclimatology
DE: 3349 Polar meteorology
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting