Longitudinally different variations of lower tropospheric carbon dioxide concentrations over the North Pacific Ocean

To elucidate temporal and spatial variations of the atmospheric CO₂ concentration over the North Pacific Ocean, air samples have been collected systematically using 4 container ships for 3 years from 1984 to 1986. The seasonal CO₂ cycle was most enhanced at high latitudes and decreased gradually going southward with a phase delay. North of 30°N, the seasonal amplitude was larger in the western part than in the eastern part; however, to the south the situation was reversed. The southward phase shift of the seasonal CO₂ cycle was much reduced in the eastern part, as compared with that in the western part. In the western part, the annual mean values of the CO₂ concentration in respective years were high at middle latitudes and decreased going southward and northward; those in the eastern part were rather constant at middle and high latitudes, but increased slightly with decreasing latitude. As a result, yearly mean CO₂ concentrations between 50° and 25°N were always higher in the western part than in the eastern part and those at lower latitudes showed the opposite distribution. Differences of the CO₂ concentration between the eastern and western parts depended on season and latitude.