HR: 09:30h
AN: C31C-06    [Abstracts]
TI: Firn Physical Characteristics and Impact on Interstitial Convection and Diffusion in the Megadunes of East Antarctica
AU: * Courville, Z R
EM: zoe.courville@dartmouth.edu
AF: Thayer School of Engineering Dartmouth College, 8000 Cummings Hall, Hanover, NH 03755 United States
AU: * Courville, Z R
EM: zoe.courville@dartmouth.edu
AF: Cold Regions Research & Engineering Lab, 72 Lyme Road, Hanover, NH 03755 United States
AU: Albert, M R
EM: mary.r.albert@erdc.usace.army.mil
AF: Thayer School of Engineering Dartmouth College, 8000 Cummings Hall, Hanover, NH 03755 United States
AU: Albert, M R
EM: mary.r.albert@erdc.usace.army.mil
AF: Cold Regions Research & Engineering Lab, 72 Lyme Road, Hanover, NH 03755 United States
AU: Severinghaus, J
EM: jseveringhaus@ucsd.edu
AF: Scripps Institute of Oceanography, University of California San Diego, San Diego, CA 92093 United States
AB: Snow and firn properties and layering control interstitial transport of gases and vapor at all levels in the firn, along with air-snow transport in the near-surface firn. Knowledge of the properties and an understanding of interstitial transport mechanisms are important for interpretation of ice core and firn air records. Climate factors such as temperature and accumulation rate influence the physical properties of the firn, affecting feedbacks between the properties of the firn and interstitial transport mechanisms. In this paper we report on measurements of the physical properties of the firn in a megadunes region, and we model several types of convection likely to occur there. Megadunes are low relief, long wavelength wave-like features covering an extensive amount of Eastern Antarctica. The region experiences very low temperatures, -45 to -60 C mean annual temperature, and very low accumulation rates, 7 to 35 mm yr-1, which leads to extreme metamorphism of the firn crystals as they remain exposed to the surface for long periods of time. We have measured the transport properties of permeability and diffusivity, along with density, stratigraphy and microstructure characteristics of the top 30m of an ice core drilled in a megadunes region of East Antarctica. Permeability, density and grain scale measurements for the top several meters were also made in the field at a site adjacent to the ice core drilling. The permeability of the megadunes site is several times higher than that measured at Siple Dome. Diffusivity, measured with 10 cm resolution down the length of the core, follows an overall trend which is similar to the permeability profile. Crystal photography of several different types of microstructure encountered is shown. Multidimensional finite element modeling results of interstitial air movement due to ventilation, and also due to buoyancy-induced natural convection are presented. Ventilation, enhanced by cracks typical at low accumulation sites, is likely to influence near-surface properties, sublimation, and interstitial gas transport. Because of the extreme firn metamorphism and increased permeability, natural convection is also likely to play a large role in deep convection with interstitial transport at this and other low-accumulation sites.
DE: 9310 Antarctica
DE: 3210 Modeling
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting