Trajectory analysis of the atmospheric carbon dioxide bimodal distribution in the arctic

An examination of detrended atmospheric CO2 time series from two arctic monitoring stations, Alert and Mould Bay, shows a very prominent seasonal cycle with a very broad maximum in the winter and a very sharp minimum in the late summer. The amplitude of the cycle is about 15 to 16 ppmv (parts per million by volume). This seasonal cycle is a reflection of the metabolic cycle of the land biota in the northern hemisphere. During the period of broad maximum concentration in winter, the time series of CO2 shows, in some years, a bimodal feature, with a relative minimum in late winter. The bimodal distribution is difficult to explain in terms of (1) photosynthetic/respiratory cycle of terrestrial biospheric activities in the middle latitudes, and (2) anthropogenic activities. In this paper, the authors will speculate and discuss the bimodal feature in terms of the evolution of the atmospheric circulation in the Arctic