SULFATE AND NITRATE FIRN CONCENTRATIONS ON THE GREENLAND ICE-SHEET - 2 - TEMPORAL ANTHROPOGENIC DEPOSITION CHANGES

Intercomparison of three new chemical ice core records from northern G reenland (covering the time span from approximately 1500 A.D. to prese nt) with previously published records for southern and central Greenla nd reveals a uniform timing of anthropogenic changes in sulfate and ni trate firn concentrations over the entire ice sheet. The anthropogenic sulfate increase started around 1890, was interrupted by a transient decrease in the 1930s, and has resumed a major increase since 1950. Si nce the late 1970s though, a significant 30% decline in Greenland sulf ate firn levels can be documented. The maximum anthropogenic increase in northern Greenland sulfate firn concentrations (up to 200-230 ppb) is 2-3 times larger than in southern and central Greenland. Nitrate re cords show an essentially steady increase since 1950 and, documented f or the first time, a slight reduction during most recent years. Maximu m nitrate fun levels of 100-130 ppb exceed the preindustrial backgroun d by 100% all over the Greenland ice sheet. Comparison with anthropoge nic SO2 and NO, emission records indicates that the major increase in sulfate fun concentrations since 1950 can be attributed to Eurasian so urces, while fim levels during the first half of this century appear t o be dominated by North American emissions. A stronger North American source contribution is indicated over the entire 20th century in the c ase of nitrate. Applying a macroscopic deposition model separate time series for wet and dry deposition were derived which revealed a close correspondence of wet deposited sulfate with the timing of U.S. emissi ons, while the temporal evolution of Eurasian emissions is mainly refl ected in the dry sulfate deposition record. During this century wet su lfate deposition increased by a factor of two while the total dry sulf ate deposition flux increased by more than 500%. Wet and dry nitrate d eposition both increased by 100% during the same period.