18:15 〜 19:30
[ACG36-P09] スバールバル諸島ニーオルスンにおける大気中酸素濃度連続観測
キーワード：大気中酸素濃度, 炭素循環, O2:CO2交換比, 大気-海洋間O2フラックス
Simultaneous observations of atmospheric O2 (defined as O2/N2 ratio) and CO2 concentrations provide valuable information about the global carbon cycle. For a better understanding of the global carbon cycle, several laboratories have developed precise measurement systems for the O2/N2 ratio and carried out systematic observations since the early 1990s. To elucidate the variations of the atmospheric O2/N2 ratio in detail and to contribute to a better understanding of the role of Arctic region on the regional and global carbon cycle, we developed a continuous measurement system using a differential fuel-cell O2 analyzer, and then initiated systematic observation at Ny-Ålesund, Svalbard in November 2012, which is the first continuous observation in the Arctic region. The system is equipped with NDIR analyzer to measure CO2 concentration simultaneously. The analytical precisions of O2/N2 ratio and CO2 are estimated to be ±1.4 per meg and ±0.03 ppmv, respectively. Here, we will present observational results of the first year.
The O2/N2 ratio observed at Ny-Ålesund shows a clear seasonal cycle with peak-to-peak amplitude of about 120 per meg, which reaches a minimum in late March to early April and a maximum in August. On the other hand, the CO2 concentration varies seasonally in opposite phase with the O2/N2 ratio, showing the amplitude of 16 ppm. Short-term variations on time scales of several hours to several days are also clearly seen. In winter, it is often observed that the O2/N2 ratio sharply declines in a short time, accompanied by an increase in the CO2 concentration, and the low values last for several hours or days. The O2:CO2 exchange ratio defined as the slope of a linear regression line between the measured values of O2/N2 ratio and CO2 range between -1.6 and -1.5 ppm/ppm, which are close to the average O2:CO2 exchange ratio expected from fossil fuel burning in Europe. The results of backward trajectory analysis indicated that the air masses arrived at Ny-Ålesund during the periods when such short-term variations were observed passed near or over Scandinavian Peninsula. Therefore, such a decline in the O2/N2 ratio is ascribed to transport of urban air influenced by human activities in Europe. In spring to summer, irregular fluctuations of O2/N2 ratio are often observed. The amplitude of such fluctuations reaches 50-60 per meg (corresponding to about 10-13 ppm). Similar fluctuations of CO2 are also found in opposite phase with O2/N2 ratio. However, their amplitudes are 5 ppmv at most. The comparison of backward trajectories of air parcels with the distributions of marine biotic net primary production suggests that such fluctuations of O2/N2 ratio are closely related to O2 emission due to marine biological activity near Norwegian Sea.
The O2/N2 ratio observed at Ny-Ålesund shows a clear seasonal cycle with peak-to-peak amplitude of about 120 per meg, which reaches a minimum in late March to early April and a maximum in August. On the other hand, the CO2 concentration varies seasonally in opposite phase with the O2/N2 ratio, showing the amplitude of 16 ppm. Short-term variations on time scales of several hours to several days are also clearly seen. In winter, it is often observed that the O2/N2 ratio sharply declines in a short time, accompanied by an increase in the CO2 concentration, and the low values last for several hours or days. The O2:CO2 exchange ratio defined as the slope of a linear regression line between the measured values of O2/N2 ratio and CO2 range between -1.6 and -1.5 ppm/ppm, which are close to the average O2:CO2 exchange ratio expected from fossil fuel burning in Europe. The results of backward trajectory analysis indicated that the air masses arrived at Ny-Ålesund during the periods when such short-term variations were observed passed near or over Scandinavian Peninsula. Therefore, such a decline in the O2/N2 ratio is ascribed to transport of urban air influenced by human activities in Europe. In spring to summer, irregular fluctuations of O2/N2 ratio are often observed. The amplitude of such fluctuations reaches 50-60 per meg (corresponding to about 10-13 ppm). Similar fluctuations of CO2 are also found in opposite phase with O2/N2 ratio. However, their amplitudes are 5 ppmv at most. The comparison of backward trajectories of air parcels with the distributions of marine biotic net primary production suggests that such fluctuations of O2/N2 ratio are closely related to O2 emission due to marine biological activity near Norwegian Sea.