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Significant Bomb  14 C Enrichment in Deep Soil: A Previously Unrecognized Decadal C Pool? W. Troy Baisden and Roger L Parfitt Landcare Research, Palmerston.

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Presentation on theme: "Significant Bomb  14 C Enrichment in Deep Soil: A Previously Unrecognized Decadal C Pool? W. Troy Baisden and Roger L Parfitt Landcare Research, Palmerston."— Presentation transcript:

1 Significant Bomb  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 US-NZ Climate Change Partnership through NZ Govt

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

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 Soil Organic Matter Inputs Outputs

7 The Model DOM v DOM k DOM Concentration

8 Model Formulation for DRDSC (Decadally Reactive Deep Soil C) Mass (g/m 2 ) 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  14 C 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

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13 Koputaroa Soil, New Zealand  14 C (per mil) Cumlative Soil Mass (g cm -2 )

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16 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! 10-20% of Deep Soil C has Decadal Dynamics Possibly increasing with Depth? Better understanding of DOC needed! Koputaroa


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