A 250-YEAR, VERY HIGH-RESOLUTION RECORD OF TRACE ELEMENT DEPOSITION IN CENTRAL GREENLAND

Using a new method for continuous trace element measurements in ice cores, we developed a very high-resolution, 1750 to 1998 record of Na, Mg, Al, Mn, Rb, Sr, Zr, Ba, Nd, and Pb concentrations and fluxes from a central Greenland ice core. Previous trace metal measurements in polar snow and ice were based on discrete sampling methods. Because of the extensive decontamination procedures needed to prepare discrete samples and the large sample volumes required, these studies were limited in depth resolution and in the range of depths sampled (often spanning only a few years to decades). In the most exhaustive ice core studies, temporal resolution was generally no more than two samples per year. With this new analytical method, melt from a continuous ice core melter is input in real time to an Inductively Coupled Plasma Mass Spectrometer for elemental measurements and to a continuous flow analysis system for NH₄, NO₃, and H₂O₂ determinations. To minimize potential contamination, only melt from the innermost region of a longitudinal sample is analyzed, with melt from the potentially contaminated outer region discarded. The result is a measurement of total analyte concentrations (soluble and insoluble fraction), thus providing exactly dated and co-registered elemental fingerprints of continental dust, volcanic particles, pollution aerosols, and sea salt deposited to the ice sheet over recent centuries. Temporal resolution for this central Greenland core is approximately 24 samples year^-1. While interpretation of these unique records is ongoing, it is clear that continental dust fluxes to central Greenland have varied significantly over recent centuries at time scales from months to decades, with unusually large fluxes during much of the 19th century and the dust bowl years of the 1930s, but relatively small fluxes over recent decades.