In situ Winter Soil Respiration Measurements in High Arctic Environments

Abstract:

Climate warming and changing precipitation patterns are affecting the magnitude of carbon dioxide release in Arctic regions. The Arctic stores more than half of the global soil carbon pool up to three meters, and continued warming threatens the release of this carbon to the atmosphere. While there are several examples of growing-season measurements of carbon exchange in the High Arctic, there are far fewer examples of winter-time respiration measurements. Techniques like forced diffusion allow for continuous in situ measurements of surface and belowground CO₂ fluxes that can provide insight into the patterns and drivers of high latitude carbon cycling during the cold winter months.

We deployed a forced diffusion station in High Arctic mesic tundra at the Cape Bounty Arctic Watershed Observatory, Melville Island, Nunavut to investigate the impact of temperature and moisture on soil CO₂ efflux throughout the entire year. Surface chambers measured continuous CO₂ release using a gradient method, while chambers buried at 10, 25, and 50 cm belowground measured soil CO₂ concentrations. Preliminary results gathered from the surface and buried chambers at the peak and end of the growing season in 2018 show strong links between CO₂ production and soil temperature fluctuations during this time. Soil CO₂ concentrations were highest in the transient layer of permafrost around 25 cm depth, and these higher fluxes persisted later into the growing season than fluxes from shallower depths. Bidirectional freezing of the soil layers contributed to pulses of high concentration CO₂ release, particularly after the fall zero curtain and before the spring zero curtain. Rates of respiration were greater in the growing season than in the non-growing season, and when considered on an annual timescale, the CO₂ released in the non-growing season was half that released during the summer. These initial results highlight the importance of non-growing season respiration as a contributor to the annual carbon budget of this High Arctic ecosystem. Future work will explore the development of improved models based on environmental measurements with the goal of predicting changes to the carbon cycle in response to changes in climate.