277 Critical Zone Science: Intersection of Processes Linked to Geomorphology, Ecology, Fire and Climate

This session welcomes interdisciplinary studies that investigate the rates and processes of soil development, regolith formation, carbon storage and the role of ecological and/or hydrologic feedbacks in shaping the landscape (both past and present).

Wednesday, 22 October 2025
1:30 PM - 5:30 PM
HBGCC, 212AB

What can we learn from carbon isotope profiles of soil organic matter?

Paper number: 277-4
Program: Technical Sessions
Time: 2:25 PM – 2:45 PM

Authors

Abstract

In hillslope and other well-drained soils, the d13C values of soil organic carbon almost always increase whereas radiocarbon activities tend to decrease with depth. These trends relate to the stabilization of organic carbon, but what, in particular, can we learn from them? We begin with an investigation of radiocarbon and distinguish between two basic conceptual models that explain generalized profiles: 1) the downward advection of soil organic carbon, which we call the ‘conveyor belt’ model, and 2) the vertical decrease in microbial carbon consumption constants, which leads to slower turnover with depth and which we term the ‘convenience store’ model. We suggest that the convenience store model may represent the priming of microbial communities by root exudates and test this idea with Bayesian inversion of profile data uisng two versions of a numerical soil carbon model, one that does and one that does not include scaling of microbial consumption with root density. We also suggest that neither endmember model is sufficient on its own and offer that we do not know how their relative importance varies with the factors of soil formation. We then present an approach involving joint inversion that should both elucidate controls on stable carbon isotope profiles and provide tight constraints on soil carbon cycling parameters. Application of these joint inversions across rooting depth and permeability gradients, and perhaps to soils undergoing woody encroachment, might be especially helpful in understanding the relative importance of the conveyor belt and convenience store.

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

doi: 10.1130/abs/2025AM-414796

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.