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. The 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 this 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 clear diurnal variation. During the snow-free period, before the onset of veaetation 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 sunny days in the middle of the growing season, the net ecosystem exchange rates attained typical values of about -0.23 mg m(-2) s(-1) at midday and max values of daily sums of -12gCO(2) m(-2) d(-1). Throughout the measured period the fen ecosystem acted as a net-sink of 130gCO(2) m(-2). Modelling the ecosystem respiration during the season corresponded well with eddy correlation 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).