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

Abstract

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_4CO, 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^, 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^, respectively. By comparing the N_2O concentrations observed at Ny-Alesund 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.