Investigating In-Depth Fractionations of Soil Radiocarbon: Insights and Applications from Thermal Analysis
Abstract
Soil organic matter (SOM) is a complex collection of organic molecules of various origin, structure, chemical activity, and mineral association. Separating this complex mixture into meaningful pools of differing stability and determining their drivers remains a major challenge for understanding carbon (C) cycling in soils. Here we present the results of a recently developed method of fractionation which relies on a conceptual analogue between biochemical stability in soil and thermal stability: more persistent SOM requires higher temperatures (greater energy inputs) to decompose than less persistent SOM. Both chemical complexity and mineral association are accounted for as main factors in determining SOM persistence, but these have so far rarely been used to systematically address their role for SOM stability. Here we analyzed thermal stability diagrams of 1) bulk soil SOM, 2) density fractions, and 3) chemical oxidation residues to identify three to five component C pools of similar thermal characteristics. During a second combustion, CO2 from each pool was isolated and analyzed for 13C and 14C. First results show that single density fractions contain a wide range of radiocarbon activities, from 1.16 to 0.95 Fm in topsoil, and that young SOM is present across multiple fractions, likely contingent on strong organomineral complexation. The highest-temperature sub-fractions contain the oldest carbon, thus supporting the assumption that thermal stability can be used as a limited analogue for stability in soil. Forthcoming analysis of additional sites and soil depths will help identify SOM stability and age distributions dependent on mineralogy, transport, and SOM loading of minerals.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B41C..07S
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0463 Microbe/mineral interactions;
- BIOGEOSCIENCES;
- 0486 Soils/pedology;
- BIOGEOSCIENCES