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Significant Bomb D 14 C Enrichment in Deep Soil: A Previously Unrecognized Decadal C Pool?

Significant Bomb D 14 C Enrichment in Deep Soil: A Previously Unrecognized Decadal C Pool?. W. Troy Baisden and Roger L Parfitt Landcare Research, Palmerston North, New Zealand. Funded by NZ Foundation for Research Science and Technology Ministry of Agriculture and Forestry

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Significant Bomb D 14 C Enrichment in Deep Soil: A Previously Unrecognized Decadal C Pool?

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  1. Significant Bomb D14C Enrichment in Deep Soil: A Previously Unrecognized Decadal C Pool? W. Troy Baisden and Roger L Parfitt Landcare Research, Palmerston North, New Zealand Funded by NZ Foundation for Research Science and Technology Ministry of Agriculture and Forestry US-NZ Climate Change Partnership through NZ Govt

  2. California Grassland Soil % Modern Carbon (1950 atmosphere) 120 80 100 60 1997 Depth (cm) 1952 ∆14C (‰, pre-bomb atm.= 0)

  3. Baisden et al 2002, Global Biogeochemical Cycles

  4. Koputaroa, New Zealand Goh et al, 1976 Syers et al, 1970

  5. Judgeford, New Zealand O’Brien and Stout, 1978

  6. Understanding Carbon Storage and Turnover • The balance between inputs and outputs Outputs Soil Organic Matter Inputs

  7. Concentration vDOM kDOM DOM The Model

  8. Model Formulation for DRDSC(Decadally Reactive Deep Soil C) • Mass (g/m2) • Downward Transport (cm/yr) • First Order Loss Coefficient (yr-1) • E-folding Depth (cm) • No interactions with other 3 pools • Is DRDSC from roots or dissolved organic matter (DOM)? • Progressive enrichment in most profiles • Below rooting zone

  9. Data Assimilation via a Genetic Algorithm • Evolves a chromosome of parameter values toward the best value for the model fit (based on an ‘objective function’) • Inefficient but searches parameter space on both sides of the bomb-C spike • Monte-Carlo style variation in D14C and %C data • Parameter uncertainty estimated from Monte-Carlo • Greater of: • Standard deviation of best fits with data PDFs • Difference between best fit with and without PDFs included • Emphasizing fitting DRDSC pool sizes

  10. Koputaroa Soil, New Zealand Cumlative Soil Mass (g cm-2) D14C (per mil)

  11. Koputaroa DRDSC as a Fraction of Total SOC • 10-20% of Deep Soil C has Decadal Dynamics • Possibly increasing with Depth? • Better understanding of DOC needed!

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