北極域陸域生態系の炭素循環とメタン動態

抄録

This review demonstrates carbon cycle and methane dynamics in the Arctic ecosystem, which plays an important role in carbon dioxide and methane emissions because of large stocks of soil organic matter, rapid Arctic warming, and permafrost thaw. Exchange of carbon dioxide between terrestrial ecosystem and the atmosphere is determined by the balance between ecosystem respiration and primary production. Ecosystem respiration can be enhanced not only by soil temperature increase during the summer but also that during the autumn and the winter. Vegetation change is a highly uncertain factor on primary production. Some observations reported increase of shrubs which are important species in Arctic carbon cycle. Tree line is predicted to shift northward under Arcitic warming, and observational studies suggest that the shift depends on seed dispersal or microtopography and hydrology of permafrost ecosystem. Effects of climate change such as snow increase on vegetation have been also investigated by in situ manipulation experiments.

Effect of permafrost thaw on methane emission has been assessed by observing methane flux across sites with different permafrost conditions. Satellite imagery can be used to evaluate changes in wetland area by permafrost thaw and to estimate methane emission changes on local or regional scales. Production, oxidation, and transport processes of methane, which are necessary for understanding the relations between methane emission and environmental factors, can be assessed by carbon and hydrogen isotopes of methane.