HR: 0800h
AN: C51A-0106    [Abstracts]
TI: Lagrangian Transient Firn Compaction Model With Heat Transfer
AU: * Lundin, J
EM: jdrees@u.washington.edu
AF: University of Washington, Johnson Hall 070, Box 351310, 4000 15th Avenue NE, Seattle, WA 98195-1310, United States
AU: Waddington, E
EM: edw@ess.washington.edu
AF: University of Washington, Johnson Hall 070, Box 351310, 4000 15th Avenue NE, Seattle, WA 98195-1310, United States
AB: Paleoclimate applications require knowledge of the ice-age gas-age offset (delta age) to correlate proxies in the ice (e.g. the temperature proxy δ18O in H2O) with trapped atmospheric gas. We develop a modular one-dimensional Lagrangian transient firn compaction model to find delta age. Finite volumes proportional to surface accumulation are advected downward, as they thin vertically primarily due to increases in density. The volumes can also extend horizontally due to strain in the underlying ice sheet. The evolution of each finite volume is governed by mass conservation and a constitutive relation for firn. Firn-compaction rate depends on temperature, so the compaction model is coupled to a Lagrangian heat-diffusion model, in which the thermal properties can depend on density. Upper boundary conditions for the coupled model are the histories of accumulation rate, surface density, and surface temperature. The lower boundary conditions must be provided from a larger ice-sheet model in which the firn model can be embedded. These conditions are the the thermal boundary condition, horizontal extension with depth, and vertical velocity at the bottom of the firn. Delta age is defined as the age of the ice where the density of bubble close of is met. The firn model can be incorporated into a larger inverse problem, creating a self-consistent system among three lines of questioning, that have until now been treated independently: (1) delta-age (2) inferred spatial and temporal accumulation histories from dated radar layers, and (3) physically meaningful interpolations of depth-age between sparse dated gas data points. This firn compaction model with a modular design, can be applied to any ice sheet given the requisite boundary conditions, further contributing to frontier work in ice sheet modeling.
DE: 0724 Ice cores (4932)
DE: 0726 Ice sheets
DE: 0798 Modeling
SC: Cryosphere [C]
MN: 2007 Fall Meeting