Dynamics of deep soil carbon – insights from 14C time series across a climatic gradient

Van der Voort Tessa Sophia 1, Mannu Utsav 1, Hagedorn Frank 2, McIntyre Cameron 3, Walthert Lorenz 2, Schleppi Patrick 2, Haghipour Negar 1, Eglinton Timothy Ian 1

1 Geological Institute, ETH Zurich, CH-8092 Zurich, Switzerland
2 Swiss Federal Institute for Forest, Snow, and Landscape Research (WSL), Zürcherstrasse 111, CH-8903 Birmennsdorf, Switzerland
3 Scottish Universities Environmental Research Centre (SUERC), East Kilbride G75 0QF, Scotland

Biogeosci. 16 (2019): 3233-3246

DOI: 10.5194/bg-16-3233-2019


Quantitative constraints on soil organic matter (SOM) dynamics are essential for comprehensive understanding of the terrestrial carbon cycle. Deep soil carbon is of particular interest as it represents large stocks and its turnover times remain highly uncertain. In this study, SOM dynamics in both the top and deep soil across a climatic (average temperature ~1-9 °C) gradient are determined using time-series (~20 years) 14C data from bulk soil and waterextractable organic carbon (WEOC). Analytical measurements reveal enrichment of bomb-derived radiocarbon in the deep soil layers on the bulk level during the last 2 decades. The WEOC pool is strongly enriched in bomb-derived carbon, indicating that it is a dynamic pool. Turnover time estimates of both the bulk and WEOC pool show that the latter cycles up to a magnitude faster than the former. The presence of bomb-derived carbon in the deep soil, as well as the rapidly turning WEOC pool across the climatic gradient, implies that there likely is a dynamic component of carbon in the deep soil. Precipitation and bedrock type appear to exert a stronger influence on soil C turnover time and stocks as compared to temperature.