The Effects of Physical and Biogeochemical Changes on Carbon Emissions from Mineral Cryosols from the Canadian High Arctic

Abstract

The Arctic regions contain vast stores of organic carbon within the permafrost, isolated from the current global carbon cycle. Changes in global climate, however, are likely to place this carbon pool at risk of degradation as temperatures increase at high northern latitudes and the extent of continuous permafrost decreases. Changes in the temperature and hydrology of permafrost systems will affect total carbon loss from polar regions and the balance of CO2 to CH4 emissions. This study examined how changes in Arctic mineral cryosols will extend to carbon emissions, geochemical conditions, and microbial community composition over time at Axel Heiberg Island, Nunavut, Canada.

Intact core experiments were used to simulate the conditions of spring thawing in permafrost while examining the effects of permafrost degradation under conditions of soil saturation, light limitation, and soil location. Low soil saturation and permafrost thawing stimulated emissions of CO2 from mineral cryosols, though CH4 oxidation was observed in all soils following thaw, regardless of treatment condition. Long term (76 week) thawing of permafrost significantly increased CO2 emissions regardless of treatment conditions and increased over time. Intact core CO2 emissions profiles behaved differently from microcosm CO2 emissions from the same soils, suggesting shorter soil organic carbon turnover times as well as incongruities between the two methodologies. CH4 oxidation potential was independent of treatment condition but uniformly decreased over 18 months of thaw, reducing a net CH4 sink to a CH4-neutral soil. Furthermore, the microbial composition of the mineral cryosols was not found to substantially change over the course of thawing, despite changes in both flux and geochemical parameters.

Microcosm experiments were conducted to examine the CH4 oxidation potential of mineral cryosols at atmospheric CH4 concentrations as a function of water saturation, temperature, and soil column depth. CH4 oxidation was found to be highest at higher temperatures and within the top 35 cm of the soil, a finding in line with the microbial abundance of methanotrophic bacteria within the top 1 m. Additionally, methanotrophic bacteria at Axel Heiberg Island were found to have a significantly higher activity compared to other locations in the Arctic.