Sulfur Isotopic Measurements from a West Antarctic Ice Core: Implications for Sulfate Source and Transport

Measurements of delta(34)S covering the years 1935-76 and including the 1963 Agung (Indonesia) eruption were made on a West Antarctic firn core, RIDSA (78.73 degrees S, 116.33 degrees W; 1740m a.s.l.), and results are used to unravel potential source functions in the sulfur cycle over West Antarctica. The delta(34)S values Of SO42- range from 3.1 parts per thousand to 9.9 parts per thousand. These values are lower than those reported for central Antarctica, from near South Pole station, of 9.3-18.1 parts per thousand (Patris and others, 2000). While the Agung period is isotopically distinct at South Pole, it is not in the RIDSA dataset, suggesting differences in the source associations for the sulfur cycle between these two regions. Given the relatively large input of marine aerosols at RIDSA (determined from Na+ data and the seasonal SO42- cycle), there is likely a large marine biogenic SO42- influence. The delta(34)S values indicate, however, that this marine biogenic SO42-, with a well-established delta(34)S of 18 parts per thousand, is mixing with SO42- that has extremely negative delta(34)S values to produce the measured isotope values in the RIDSA core. We suggest that the transport and deposition of stratospheric SO42- in West Antarctica, combined with local volcanic input, accounts for the observed variance in delta(34)S values.

Impact of Preindustrial Biomass-Burning Emissions on the Oxidation Pathways of Tropospheric Sulfur and Nitrogen

Ice core measurements (H2O2 and CH4/HCHO) and modeling studies indicate a change in the oxidation capacity of the atmosphere since the onset of the Industrial Revolution due to increases in fossil fuel burning emissions [e. g., Lelieveld et al., 2002; Hauglustaine and Brasseur, 2001; Wang and Jacob, 1998; Staffelbach et al., 1991]. The mass-independent fractionation (MIF) in the oxygen isotopes of sulfate and nitrate from a Greenland ice core reveal that biomass-burning events in North America just prior to the Industrial Revolution significantly impacted the oxidation pathways of sulfur and nitrogen species deposited in Greenland ice. This finding highlights the importance of biomass-burning emissions for atmospheric chemistry in preindustrial North America and warrants the inclusion of this impact in modeling studies estimating changes in atmospheric oxidant chemistry since the Industrial Revolution, particularly when using paleo-oxidant data as a reference for model evaluation.