Ramped oxidation and fine scale serial ¹⁴ C analyses of saltmarsh soils

Abstract

Combined ramped oxidation and radiocarbon analysis (RO- ¹⁴ C) determines the age of carbon pools that have differing thermochemical stability (decomposability), providing powerful insights for studying the carbon cycle. We performed RO- ¹⁴ C of surface soils from a saltmarsh and dated the narrowest temperature intervals so far undertaken for any samples, finding that no modern (post-bomb) ¹⁴ C contents were resolved. We compared these ramped oxidation measurements to the ¹⁴ C content of respired CO ₂ from the same soils, demonstrating that the most biologically available organic carbon was younger (more ¹⁴ C-enriched) than any of the thermal fractions for surface soils. In our saltmarsh soils, ramped oxidation alone is therefore not able to isolate both the youngest and the most biologically available OC pools. However, we show that a combined approach of RO- ¹⁴ C and measurements of the ¹⁴ C content of respired CO ₂ (e.g., incubation experiments) may provide more powerful insights for unravelling carbon cycling.