Temporal variations of atmospheric greenhouse gases and their related gases at Syowa Station, Antarctica and Ny-Ålesund, Svalbard

To elucidate temporal variations of greenhouse gases and their related gases in the Arctic and Antarctic regions and to investigate their sources and sinks, systematic measurements of atmospheric CO ₂, CH ₄, CO, N ₂O, O ₂ and tropospheric O ₃ concentrations have been carried out at Syowa Station, Antarctica and Ny-Alesund, Svalbard. The CO ₂ concentrations at both polar sites have increased at a rate of about 1.9 ppmv yr ^-1, reflecting fossil fuel combustion and land use change. The CH ₄ concentrations also showed clear seasonal cycles superimposed on complex secular trends. The increase rate of the CH ₄ concentration varied with time. CH ₄ increases were observed until 1999, the concentrations remained steady from 2000 to 2006 and then rapid increases were observed in 2007. Stable isotope data of CH ₄ revealed causes of the seasonal cycles and the secular variations of the CH ₄ concentrations. The O ₂ concentrations (δ(O ₂/N ₂)) at both polar sites showed prominent seasonal cycles and secular decreasing trends. From analyses of the Atmospheric Potential Oxygen (APO) and CO ₂ concentrations, the CO ₂ uptake rates by the terrestrial biosphere and the ocean were estimated to be 1.1 and 2.7 GtC yr ^-1, respectively. By comparing the N ₂O concentrations observed at Ny-Ålesund and numerical model results, it was suggested that the observed seasonal N ₂O cycle could be enlarged by intrusion of a stratospheric air mass with low N ₂O concentration into the troposphere in summer. With an analysis using a three dimensional chemical-transport model and the CO concentration at Syowa Station, sporadic increases of CO concentration observed in February-March, 2003 and February, 2007 were ascribed to CO release by large-scale forest fires in Australia. Surface ozone depletion events were observed more than 40 times at Syowa Station from 1988 to 2007.