Seasonal carbon dioxide balance and respiration of a high-arctic fen ecosystem in NE-Greenland

Turbulent fluxes Of CO2 were continuously measured by eddy correlation for three months in 1997 over a gramineous fen in a high-arctic environment at Zackenberg (74 degrees 28'12 " N, 20 degrees 34'23 " W) in NE-Greenland. Th e measurements started on I June, when there was still a 1-2 m cover of dry snow, and ended 26 August at a time that corresponds to late autumn at thi s high-arctic site. During the 20-day period with snow cover, fluxes Of CO2 to the atmosphere were small, typically 0.005 mg CO2 m(-2) s(-1) (0.41 gCO (2) m(-2) d(-1)), wheres during the thawed period, the fluxes displayed a c lear diurnal variation. During the snow-free period, before the onset of ve aetation growth, fluxes of CO2 to the atmosphere were typically 0.1mg,CO2 m (-2) s(-1) in the afternoon and daily sums reached values up to almost 9gCO (2)m(-2) d(-1). After 4 July, downward fluxes Of CO2 increased, and on sunn y days in the middle of the growing season, the net ecosystem exchange rate s attained typical values of about -0.23 mg m(-2) s(-1) at midday and max v alues of daily sums of -12gCO(2) m(-2) d(-1). Throughout the measured perio d the fen ecosystem acted as a net-sink of 130gCO(2) m(-2). Modelling the e cosystem respiration during the season corresponded well with eddy correlat ion and chamber measurements. On the basis of the eddy correlation data and the predicted respiration effluxes, an estimate of the annual CO2 balance the calender year 1997 was calculated to be a net-sink of 20gCO(2) m(-2) yr (-1).