Recrystallization of pedogenic and biogenic carbonates in soil: environmental controls, modelling and relevance for paleoenvironmental reconstructions

• Applicant: Professor Dr. Yakov Kuzyakov
• Subject Area: Soil Sciences ; Physical Geography
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 276710838

Isotopic signatures of pedogenic and biogenic carbonates are the most important tools for radiocarbon dating of soils and for reconstructing paleoenvironments under semiarid and arid climates. Recrystallization of carbonates with soil CO2, however, may shift their C and O isotopic signatures and therefore bias the reconstruction results. This calls for corrections considering the recrystallization of carbonates. The self-developed and already proven approach involving isotopic exchange of carbonates with 14CO2 will be used to analyze recrystallization rates of the most common forms of pedogenic and biogenic carbonates depending on environmental conditions. This will enable to evaluate which carbonate materials are the most useful for paleoenvironmental reconstructions and which conditions best preserve their isotopic signature. In a first step we will demonstrate the effects of abiotic factors - soil CO2 concentration, moisture, temperature, time and the presence of diffuse geogenic carbonates - on the recrystallization rates of 3 groups of pedogenic (nodules, stone coatings, laminar caps) and 3 biogenic carbonates (shells, bone pieces, calcified seeds). Furthermore, we will analyze the effects of biotic factors - root respiration and exudation - in experiments with 4 plants with different root properties. The experimentally obtained recrystallization rates will be used to parameterize the model simulating total recrystallization of pedogenic and biogenic carbonates under various experimental conditions. Finally, the model will be proven by comparing simulated recrystallization with radiocarbon and U/Th dating of pedogenic and biogenic carbonates sampled in archaeological sites. The results of this project will allow researchers to select the most suitable pedogenic and biogenic carbonates for dating and paleoenvironmental reconstructions depending on the environmental and biotic factors, and will provide reliable corrections for possible recrystallization.

• DFG Programme: Research Grants
• Co-Investigators: Professorin Dr. Michaela Dippold; Kazem Zamanian, Ph.D.