HR: 1340h
AN: C33C-0359    [Abstracts]
TI: Firn density profile at Megadunes, East Antarctica, calls for an improved densification model for low accumulation sites.
AU: * Suwa, M
EM: msuwa@princeton.edu
AF: Department of Geosciences, Princeton University, Guyot Hall, Washington Rd., Princeton, NJ 08544 United States
AU: Severinghaus, J P
EM: jseveringhaus@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, Vaughan Hall, 8675 Discovery Way, La Jolla, CA 92037 United States
AB: We report a density profile of the firn at Megadunes, East Antarctica (80$^{o}$78'S; 124$^{o}$50'E). The Megadunes site is characterized by a low mass accumulation rate (2.9 g/cm$^{2}$/yr) and cold temperature (mean annual = -49.5$^{o}$C). Validating existing firn densification models using a density profile of such a site is important because such models, either purely empirical or mechanistic, have been calibrated with few sites that are analogous to a glacial condition (ultralow accumulation and temperature). We make use of CO$_{2}$ concentrations in the lock-in (or non-diffusive) zone to obtain the accumulation rate, assuming that the gas in the lock-in zone ages at the same rate as the surrounding ice [Battle et al., 1996], and assuming that the gas enclosure rate must equal the long-term mean accumulation rate. This estimate is preliminary and may change when results from beta analysis of cores become available. Our density profile shows that the widely used pure empirical model by Herron and Langway [1980] overestimates the close-off depth by 16 %, and the semi-mechanistic model by Pimienta and Barnola [Barnola et al., 1991] also overestimates the close-off depth by 26 %. Our study at the Megadunes site indicates that the $\delta$$^{15}$N of N$_{2}$ paradox for glacial ice from East Antarctica would have partly resulted from a poorly calibrated densification model for a `glacial-like' condition and a thick convective zone as we observed at the Megadunes site [Severinghaus et al., in prep].
DE: 9310 Antarctica
DE: 3344 Paleoclimatology
DE: 1827 Glaciology (1863)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting