Soil Carbon Dynamics Reshaped by Ancient Carbon Quantification

Area of Science:

• Geochemistry
• Soil Science
• Climate Science

Background:

• Soil organic carbon (SOC) is a critical terrestrial reservoir for climate change mitigation.
• Radiocarbon dating of SOC is essential but complicated by ancient, radiocarbon-free organic carbon (aOC).
• Existing estimates of SOC age are potentially inaccurate due to unaddressed aOC.

Purpose of the Study:

• To quantify the global distribution of aOC in soils.
• To correct radiocarbon-based SOC age estimates by accounting for aOC.
• To reconcile empirical data with Earth system model parameterizations.

Main Methods:

• Applied a linear mixing equation to 313 global soil samples from radiocarbon databases.
• Quantified aOC content and its contribution to total SOC across different soil depths.
• Subtracted aOC contributions to calculate corrected SOC ages.

Main Results:

• Mean aOC content is 2.4 mg/g, contributing up to 11% in topsoils, 25% in subsoils, and over 50% in deep soils.
• Andosols and Cryosols exhibit particularly high aOC content.
• Corrected mean age of non-aOC carbon to 1m depth is 290 years, significantly younger than previous estimates (3100–4830 years).

Conclusions:

• The presence of aOC significantly skews radiocarbon-based SOC age estimates.
• Corrected SOC age aligns better with other isotopic proxies and empirical data.
• This study provides a more accurate understanding of soil carbon dynamics for improved climate modeling.