Modeling Air Movement in the Firn at WAIS-D Mark Battle Bowdoin College WAIS-D meeting NICL July 16, 2006

Possible firn modeling strategies: Forward model, diffusion only (Schwander etc.) Inverse model, diffusion only (Butler et al.1999) Inverse model, diffusion only, a’la Rommelaire Forward model, diffusion & heat (Severinghaus et al ) Forward model, diffusion & close-off fractionation (Severinghaus & Battle, 2005 ) Other approaches?

Possible firn modeling strategies: Forward model, diffusion only (Schwander etc.) Inverse model, diffusion only (Butler et al.1999) Inverse model, diffusion only, a’la Rommelaire Forward model, diffusion & heat (Severinghaus et al ) Forward model, diffusion & close-off fractionation (Severinghaus & Battle, 2005 ) Other approaches?

Forward model, diffusion only What are its virtues? Simple Good reality check Can determine age profile vs. depth

Forward model, diffusion only Overview Measured density profile

Forward model, diffusion only Overview Measured density profile Calculate porosity and diffusivity

Forward model, diffusion only Overview Measured density profile Calculate porosity and diffusivity Tune diffusivity until one species’ observations are reproduced

Forward model, diffusion only Overview Measured density profile Calculate porosity and diffusivity Tune diffusivity until one species’ observations are reproduced Confirm(?) with other species

Forward model, diffusion only Overview Measured density profile Calculate porosity and diffusivity Tune diffusivity until one species’ observations are reproduced Confirm(?) with other species Use it

Field-measured density in various cores at WAIS-D

Fit to density, used for diffusivity starting-point.

How deep is the diffusive column?

64.84mbs

Getting started with CO 2

Correcting for Gravitational Fractionation

Getting started with CO 2

After Tuning…

Testing with other species…

Testing with CH 4

Testing with CH 3 CCl 3

Testing with F11

Testing with HFC134a

Summary of basic forward model: No big surprises!!!

Summary of basic forward model: No big surprises!!! Density-based diffusivity requires only minor tweaking

Summary of basic forward model: No big surprises!!! Density-based diffusivity requires only minor tweaking XX vs. depth looks generally good for wide range of histories

Summary of basic forward model: No big surprises!!! Density-based diffusivity requires only minor tweaking XX vs. depth looks generally good for wide range of histories “Gravitational” correction needs more data

Summary of basic forward model: No big surprises!!! Density-based diffusivity requires only minor tweaking XX vs. depth looks generally good for wide range of histories “Gravitational” correction needs more data D CH 3 CCl 3 /D CO 2 consistent with SPO

Summary of basic forward model: No big surprises!!! Density-based diffusivity requires only minor tweaking XX vs. depth looks generally good for wide range of histories “Gravitational” correction needs more data D CH 3 CCl 3 /D CO 2 consistent with SPO D F11 /D CO 2 consistent with theory (and not SPO)

Summary of basic forward model: No big surprises!!! Density-based diffusivity requires only minor tweaking XX vs. depth looks generally good for wide range of histories “Gravitational” correction needs more data D CH 3 CCl 3 /D CO 2 consistent with SPO D F11 /D CO 2 consistent with theory (and not SPO) Timing of forcing history crucial (e.g. HFC134a)

Summary of basic forward model: No big surprises!!! Density-based diffusivity requires only minor tweaking XX vs. depth looks generally good for wide range of histories “Gravitational” correction needs more data D CH 3 CCl 3 /D CO 2 consistent with SPO D F11 /D CO 2 consistent with theory (and not SPO) Timing of forcing history crucial (e.g. HFC134a) Ready to roll…

Where to next? Characterizing age spread by depth

Where to next? Characterizing age spread by depth You tell me…