Modeling Air Movementin 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. 2000 )• 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. 2000 )• Forward model, diffusion & close-off

fractionation (Severinghaus & Battle, 2005 )• Other approaches?

Forward model, diffusion onlyWhat are its virtues?

•Simple

•Good reality check

•Can determine age profile vs.

depth

Forward model, diffusion onlyOverview

Measured density profile

Forward model, diffusion onlyOverview

Measured density profile

Calculate porosity and diffusivity

Forward model, diffusion onlyOverview

Measured density profile

Calculate porosity and diffusivity

Tune diffusivity until one species’

observations are reproduced

Forward model, diffusion onlyOverview

Measured density profile

Calculate porosity and diffusivity

Tune diffusivity until one species’

observations are reproduced

Confirm(?) with other species

Forward model, diffusion onlyOverview

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?

How deep is the diffusive column?

64.84mbs

Getting started with CO2

Correcting for Gravitational Fractionation

Getting started with CO2

After Tuning…

After Tuning…

Testing with other species…

Testing with CH4

Testing with CH3CCl3

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• DCH3CCl3/DCO2 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• DCH3CCl3/DCO2 consistent with SPO• DF11/DCO2 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• DCH3CCl3/DCO2 consistent with SPO• DF11/DCO2 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• DCH3CCl3/DCO2 consistent with SPO• DF11/DCO2 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…