Time-series Trends of Trace Elements in an Ice Core from Antarctica

Trace element measurements were made by instrumental neutron activation analysis on stratigraphically dated ice core samples from Byrd Station, Antarctica, to determine the concentration levels of natural and anthropogenic substances. Sampling was continuous between 1926 A.D. and 1989 A.D. and selective between 1711 A.D. and 1926 A.D. Twenty-one elements with concentrations above the detection limits were determined. The time period between 1969 A.D. and 1989 A.D. showed an enhanced impact on the Antarctic ice sheets from natural sources in the form of marine and crustal aerosols. A disturbed ocean-atmosphere interface due to El Niflo Southern Oscillation (ENSO) events seems to be a candidate especially for the enhanced marine aerosol deposition in Antarctica. Time-series trend of the concentration of deposited aluminum, which is mainly a crustal aerosol related element, shows a strong negative correlation with the time-series trend of annual average total column ozone concentrations homogenized between the 600 S and 900 S latitudes from the Total Ozone Mapping Spectrometer (TOMS) ozone data set. Although the time period is not long enough to draw a strong conclusion (1979-1989), the special role of crustal origin clay minerals on cloud nucleation dynamics might be a factor in the heterogeneous stratospheric ozone depletion chemistry through polar stratospheric cloud dynamics, assuming some troposphere-stratosphere mixing of these aerosols. The correlation of antimony and arsenic enrichments with known or suspected volcanic events was established. These marker elements was shown to be useful especially for the identification of specific historical volcanic events with low sulfur emissions. Although a clear anthropogenic impact was not observed, concentrations of arsenic, chromium, and zinc, which might come from both natural and anthropogenic sources, indicated an increase after 1960's. Principal component factor analysis indicated a possible transition-metal (especially manganese and iron) catalyzed bromine chemistry cycle, which has been suggested as the cause of tropospheric surface-level ozone depletion observed in Greenland. Calculated snow-to-air scavenging ratios indicated more efficient scavenging for crustal aerosols followed by marine and volatile elements. A new method was developed for direct air content determination in small deep ice core samples through the measurement of enclosed argon gas by instrumental neutron activation analysis. Thesis Supervisor: Dr. Ilhan Olmez Title: Principal Research Scientist, MIT Nuclear Reactor Laboratory, and Department of Nuclear Engineering Thesis Reader: Prof. Chester C. Langway, Jr. Title: Professor of Geology, SUNY, Buffalo (Emeritus)