On the physical controls of the carbon dioxide balance at a high Arctic site in Svalbard

 Current predictions of the effects of climate change indicate that the Arctic may experience a larger than average increase in temperature with consequent changes to the length of the snow-free active summer period, winter snow depth and amount and frequency of summer precipitation being highly probable. This paper reports on measurements of carbon dioxide flux at a high arctic site at Ny-Ålesund (78° 56′ N, 11° 55′ E), Svalbard and the physical climate variables that largely control this flux. It is shown that during three important precipitation-free periods of the active summer period, namely post snowmelt, high summer, and early autumn, the net balance between CO2 flux from the soil (due to respiration of roots and soil organisms) and CO2 assimilation by the vegetation is controlled largely by soil temperature and solar radiation. A simple combined photosynthetic assimilation-soil respiration model is shown to be capable of simulating the net CO2 flux during mid-summer, but is less proficient in the post snowmelt period and in early autumn when the simple models’ inability to simulate the effects of emergent growth and ponding during the former and senescence, freezing temperatures and dew during the latter indicates the need for a more complex descriptive model. The net CO2 flux during the measurement periods progresses from a net CO2 source of 0.3 gC m−2 d−1 during late snowmelt to a mid summer net CO2 sink of −0.39 gC m−2 d−1, returning to a net CO2 source of 0.1 gC m−2 d−1 in the early autumn. Simple extrapolation of the data indicates that, during the active summer season in 1995, this site was a net sink of CO2 of approximately − 9 gC m−2.