Potential methyl chloride and chloroform fluxes from the tundra soils in maritime Antarctica

Methyl chloride (CH₃Cl) and chloroform (CHCl₃) are important carriers of chlorine to the stratosphere, thus contribute to stratospheric ozone depletion and play important roles in the global Cl cycle. Studies showed that global warming and marine animal activities have impacted the production and emission of greenhouse gases in the Antarctic tundra environment. However, the biogeochemical halocarbon cycling is virtually remained unexplored in this ecosystem. In this study, soil samples were collected from seal colonies (SCS) and animal-free tundra (TS) on the Fildes Peninsula and penguin colonies (PCS) on the Ardley Island in the maritime Antarctica. We designed laboratory incubation experiments to study the potential fluxes of CH₃Cl and CHCl₃ under different manipulated conditions. Overall the net uptake rates of CH₃Cl in sea animal colonies are smaller than those from the animal-free tundra. All the tundra soils switched from net sinks of CH₃Cl under aerobic conditions to net sources under anaerobic conditions, indicating that the soil uptake of CH₃Cl prefers oxygenic conditions. In addition, increasing temperature accelerated the uptake of CH₃Cl in animal-free tundra (TS). However, seal colony soils (SCS) could convert from the CH₃Cl sink into the source when the temperature was enhanced to 8 °C, suggesting that soil bacterial oxidation might be the main mechanism for the CH₃Cl sinks in the tundra soils. On the other hand, the potential CHCl₃ fluxes showed large variations among the incubated soil samples. The animal-free tundra (TS) and the active penguin colony soils (PCS) presented to be sources of CHCl₃ under both aerobic and anaerobic conditions, but seal colony soils (SCS) showed a minor sink (or negligible source). The mean CHCl₃ flux showed significant positive (P<0.05) correlations with total organic carbon (TOC), total phosphorous (TP), total nitrogen (TN), and total halogen contents, indicating that the abiotic processes dominated the production. Assuming our incubated results to be representative of the potential fluxes from Antarctic tundra soils, we tentatively concluded that the Antarctic tundra soil is a potential important regional sink for methyl chloride (CH₃Cl) and a potential important source for chloroform (CHCl₃).