Chester C. Langway

Atmospheric trace metals and sulfate in the Greenland Ice Sheet

Abstract Chemical analyses of surface snow and dated deep ice core samples from central Greenland suggest that Zn, Pb and sulfate are presently being deposited there at two to three times the natural rates. No recent increases in Cd or V concentrations were observed. Pre-1900 ice shows no measurable effect of the activities of man and represents a good natural aerosol baseline. High enrichment factors relative to average crustal material were observed for Zn, Pb, Cd and sulfate in all samples indicating a natural source other than continental dust is responsible. A high temperature process or vapor phase origin for these enriched elements, possibly volcanism, seems likely.

Depositional history of artificial radionuclides in the Ross Ice Shelf, Antarctica

Abstract The annual fluxes of artificial radionuclides ( 238 Pu, 239+240 Pu, 241 Am, 137 Cs, 90 Sr and 3 H) from the atmosphere to the Ross Ice Shelf in Antarctica were determined from measurements in strata dated by 210 Pb. Recognizable sources include the U.S. tests (Mike-Ivy and Castle Hill) in the early 1950s, the U.S.S.R. tests of the early 1960s, the SNAP-9A burnup of 1964 and the French and Chinese tests in the late 1960s and 1970s. There are several problems still awaiting resolution: the differences in atmospheric chemistries of fission products and of transuranics produced in weapons tests and the anomalous fluxes of 238 Pu to the ice shelf which do not appear to reflect a one-year stratospheric residence. There is no evidence for a smearing of the fallout record as a consequence of diffusion of these radionuclides in the glacial column.

Global and local influences on the chemical composition of snowfall at Dye 3, Greenland: the record between 10 ka B.P. and 40 ka B.P.

Abstract Wisconsin Age ice from Dye 3, Greenland, shows a number ofδ18O level changes which indicate the occurrence of rapid climate transitions. In order to study the effect of climate change on geochemical fluxes we have selected several of these transitions for chemical analysis. At each transition we have measured chloride, nitrate and sulfate concentrations with 5 cm depth resolution. All three anionic species show significant variations which correlate with the measuredδ18O shifts. In general, periods of highδ18O (warm periods) have lower anion concentrations than adjacent periods of lowδ18O (cold periods). However, the relative concentration shifts are not the same for all species, indicating that the concentration variations cannot be caused only by changes in snow accumulation rate acting on a constant anion flux. In addition to these rapid concentration changes, over the last 40 ka slower, secular variations in baseline concentrations also occurred. Baseline chloride and sulfate concentrations reached maxima near time of maximum ice volume. Baseline nitrate, on the other hand, remained relatively constant until near the end of the glaciation when its concentration rose. If a constant sulfate flux is assumed, the measured sulfate concentrations imply a dependence of snow accumulation rate onδ18O for the Wisconsin which is similar to that presently observed in Greenland. The sulfate concentrations would then suggest that Wisconsin snowfall rates were, at times, as much as eight times lower than today.

Background levels of formate and other ions in ice cores from inland Greenland

Concentration levels of the organic acids HCOO− and CH3SO3−, inorganic acids NO3− and excess SO42− and ammonium were measured in pre-1900 AD ice layers from seven geographically dispersed inland sites in Greenland. Average multiple-year background concentration levels are calculated for each ion at each site from laboratory measurements of continuous core samples representing from 4 to 10 years of snow accumulation (32 to 80 individual measurements) from various time intervals. n nThe HCOO− concentration level increases from 6 ng/g in the most northern colder site to 36 ng/g in the most southern warmer site; CH3SO3− increases from 0.9 ng/g to 2.8 ng/g; NO3− decreases from 83 ng/g to 37 ng/g; excess SO42− decreases from 43 ng/g to 19 ng/g, all with variability. The distribution of the NH4+ ion shows a nearly constant level at about 6 ng/g for all sites except Dye-2 where it reaches 10 ng/g. The deposition patterns for HCOO− and NH4+ on the ice sheet suggest major contributions arrive from sources originating from the southwest of Greenland.