Radiocarbon Content of CO₂ Respired from High Arctic Tundra in Northwest Greenland

Abstract

Tundra soils contain large amounts of organic carbon (C) that might become available to microbial decomposition as soils warm. To elucidate the C sources currently sustaining CO₂ emissions from striped tundra soils (soil respiration) in Northwest Greenland, we studied the seasonal pattern and radiocarbon (¹⁴C) signature of soil respiration and of CO₂ within the pore space, respired from roots and non-root–associated microbes, and of bulk soil organic matter.

Old C pools are present in the topsoil of both barren ridges (1000–5000 yrs) and vegetated troughs (modern to 600 yrs). Before leaf-out, soil respiration was depleted in ¹⁴C relative to atmospheric CO₂, root and microbial respiration within the topsoil, demonstrating a substantial contribution of C fixed before 1950. As the growing season progressed, the contribution of older C pools decreased, but remained apparent in the soil respiration from ridges and in pore space CO₂. Soil respiration from troughs became dominated by recently fixed C.

As the active layer deepens with permafrost thaw, buried C may become an increasingly larger component of soil respiration. Detecting microbial decomposition of older C pools requires continuous monitoring of soil and microbial respiration and better constraints on soil C pools.

Acknowledgments

We thank M. Rogers, H. Kristenson, and K. Nagel for their assistance in the field, X. Xu, M. Kosh, M. Spalding, and M. Castaňeda for their assistance in the lab, S. Trumbore for suggestions on the study design and manuscript, and Thule Air Base and the KCCAMS lab for logistical support. This work was funded by the NSF Biocomplexity grant (0508408) awarded to Welker and the G. Comer Foundation.