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Controls on Firn Air Composition at WAIS-D and Summit (and elsewhere)

Controls on Firn Air Composition at WAIS-D and Summit (and elsewhere). Mark Battle Bowdoin College Jeff Severinghaus, Murat Aydin, Steve Montzka, Xavier Fain, Eric Sofen, Meaghan Tanguay Schwander, Bender, Etheridge/Trudinger/Enting. Dartmouth Firn Workshop March 10, 2008.

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Controls on Firn Air Composition at WAIS-D and Summit (and elsewhere)

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  1. Controls on Firn Air Composition at WAIS-D and Summit(and elsewhere) Mark Battle Bowdoin College Jeff Severinghaus, Murat Aydin, Steve Montzka, Xavier Fain, Eric Sofen, Meaghan Tanguay Schwander, Bender, Etheridge/Trudinger/Enting Dartmouth Firn Workshop March 10, 2008

  2. Reasons to study firn air • Connect ice-core trapped gas with atmosphere

  3. Reasons to study firn air • Connect ice-core trapped gas with atmosphere • Establish pre-direct, post-ice-core histories

  4. Reasons to study firn air • Connect ice-core trapped gas with atmosphere • Establish pre-direct, post-ice-core histories • Connect microstructure with air movement (mutually beneficial)

  5. Approaches to understanding firn air • In situ sampling

  6. Extracting firn air Surface ≤120m Firn lock-in zone Ice

  7. Extracting firn air Surface ≤120m Firn lock-in zone Ice

  8. Approaches to understanding firn air • In situ sampling • sampler materials • hydrodynamics (a.k.a. plumbing & pumping) • storage vessels • analysis (many species)

  9. Approaches to understanding firn air • In situ sampling • Modeling • choose a species • include relevant mechanisms • assume/infer atmospheric history • compare model output with observations

  10. Approaches to understanding firn air • In situ sampling • Modeling • choose a species • include relevant mechanisms • assume/infer atmospheric history • compare model output with observations

  11. The forward problem… • Posit an atmospheric history • Use the history to drive the model forward in time • Compare model predictions with observations

  12. The inverse problem… • Start with a set of firn air observations • What atmospheric history led to those data? Trial history = f (a,b,g,d,t) COS at South Pole from Montzka et al., JGR 2004

  13. Approaches to understanding firn air • In situ sampling • Modeling • choose a species • include relevant mechanisms • assume/infer atmospheric history • compare model output with observations

  14. Approaches to understanding firn air • In situ sampling • Modeling • choose a species • include relevant mechanisms • assume/infer atmospheric history • compare model output with observations

  15. Explain this…

  16. Explain this…

  17. Explain this…

  18. Explain this…

  19. Explain this…

  20. Influences on firn air composition • Overlying atmosphere • In situ chemistry • Gravitational settling • Thermal fractionation • Accumulation-based advection • Wind pumping • Escape through the ice-matrix • Buoyancy-driven convection

  21. Influences on firn air composition • Overlying atmosphere • In situ chemistry • Gravitational settling • Thermal fractionation • Accumulation-based advection • Wind pumping • Escape through the ice-matrix • Buoyancy-driven convection

  22. WAIS-D model and data F11

  23. WAIS-D model and data HFC134a

  24. Summit model and data Ethane

  25. Influences on firn air composition • Overlying atmosphere • In situ chemistry • Gravitational settling • Thermal fractionation • Accumulation-based advection • Wind pumping • Escape through the ice-matrix • Buoyancy-driven convection

  26. Fain et al. ACP 2007

  27. Fain et al. ACP 2007

  28. Influences on firn air composition • Overlying atmosphere • In situ chemistry • Gravitational settling • Thermal fractionation • Accumulation-based advection • Wind pumping • Escape through the ice-matrix • Buoyancy-driven convection

  29. WAIS-D models and data

  30. WAIS-D models and data

  31. WAIS-D models and data

  32. Influences on firn air composition • Overlying atmosphere • In situ chemistry • Gravitational settling • Thermal fractionation • Accumulation-based advection • Wind pumping • Escape through the ice-matrix • Buoyancy-driven convection

  33. Siple Dome models and data Severinghaus et al. G3 2000

  34. Influences on firn air composition • Overlying atmosphere • In situ chemistry • Gravitational settling • Thermal fractionation • Accumulation-based advection • Wind pumping • Escape through the ice-matrix • Buoyancy-driven convection

  35. WAIS-D models and data

  36. Influences on firn air composition • Overlying atmosphere • In situ chemistry • Gravitational settling • Thermal fractionation • Accumulation-based advection • Wind pumping • Escape through the ice-matrix • Buoyancy-driven convection

  37. WAIS-D models and data

  38. WAIS-D models and data

  39. Influences on firn air composition • Overlying atmosphere • In situ chemistry • Gravitational settling • Thermal fractionation • Accumulation-based advection • Wind pumping • Escape through the ice-matrix • Buoyancy-driven convection

  40. Remember this?

  41. Develop a conceptual model… 3.6 Å pores in ice lattice (á la Ikeda-Fukazawa et al. 2005) Severinghaus & Battle, EPSL 2006

  42. …and test it Severinghaus & Battle, EPSL 2006

  43. …but there are still puzzles in the data

  44. Influences on firn air composition • Overlying atmosphere • In situ chemistry • Gravitational settling • Thermal fractionation • Accumulation-based advection • Wind pumping • Escape through the ice-matrix • Buoyancy-driven convection

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