4-11 Developing a predictive framework for the seasonal timing of soil carbonate formation

Session: Recent Advances in Soil and Paleosol Science

Presenting Author:

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Abstract:

Understanding how short-term processes actively shape the solid-phase geochemistry of soils is difficult because regular field-based observations of the belowground geochemical environment are inherently challenging. This difficulty is compounded by the integrative nature of the solid-phase of soil, which is collectively impacted by thousands to tens of thousands of years of soil formation driven by vegetation and climate, which may or may not be similar to the modern-day surface environment. Soil carbonate exemplifies these challenges because it is a slowly accumulating feature of dryland soils. Stable isotope data generated from soil carbonates in modern soils has revealed its formation can be biased to different seasons within different regions, which complicates environmental reconstructions derived-from soil carbonate preserved in paleosols. To this end we conducted a long-term controlled and replicated field experiment near Bastrop, TX designed to constrain the factors driving modern-day soil carbonate formation. Daily field-based measurements of soil pore space CO₂ and O₂ enabled soil carbonate dissolution and formation signals to be disentangled from changes in soil respiration.  While dissolution of soil carbonate was consistently observed year-round in the days immediately following rainfall events, soil carbonate precipitation was seasonally restricted to a few consecutive weeks at the tail-end of the growing season (late May through early July) when water first became limiting. Subsequent rainfall events later during the summer would drive transient increases in soil respiration, but no formation was observed once the overlying grasses browned out. This is consistent with the importance of plant water uptake in calcite formation.  To investigate if our local observations of soil carbonate formation are widely applicable, we used global gridded datasets of soil moisture and vegetation data to predict the seasonal timing of carbonate formation across the globe. These results create a testable framework to evaluate if our Texas based observations are widely applicable or soil carbonate formation is controlled by different factors in different regions.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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