Interannual variability in net accumulation on the Greenland Ice Sheet: Observations and implications for mass balance measurements

Nine 24-year accumulation records from the Summit region in central Greenla nd are analyzed to separate the effects of spatial noise and interannual fl uctuations on the variability in each core. The study shows that both proce sses are equally important, with standard deviations of 25 mm water equival ent per year and 24 mm water equivalent per year, respectively. A compariso n with estimates of surface roughness based on high-resolution laser altime try of the surface indicates that in the studied region the spatial noise c an be reliably estimated from surface roughness. The response of the ice-sh eet surface to the interannual fluctuations can be estimated using a simple zero-dimensional ice-sheet response model. For the Summit region of centra l Greenland, a change in surface elevation of similar to 20 mm water equiva lent per year measured over a 5-year period, can be attributed with 95% con fidence to a trend in climate. This probability decreases rapidly as the ob servation period is shortened. For intervals greater than similar to 5 year , the probability depends only weakly on the measurement interval. This sug gests an optimum spacing of similar to 5 years between repeat elevation mea surements.