Stable Sulfur Isotope Rations from West Antarctica and the Tien Shan Mountains: Sulfur Cycle Characteristics from Two Environmentally Distinct Areas
As of 2002, Degree of Master of Science (MS) Quaternary and Climate Studies published under the auspices of the Climate Change Institute.
Abstract
Continuous snow pit and ice core samples from two distinct environments (West Antarctica and the Tien Shan mountains in central Asia) were analyzed for 6 3 4 ~ and used to assess different regional sulfur cycle characteristics. In West Antarctica, 18 continuous samples were obtained from the RIDSA ice core (78.73"S, 116.33"W, 1740 m asl), covering the years 1935 to 1976. Each sample represents from 2 to 3 years of snow deposition, and the combination of summer and winter seasons varies by sample. 6 3 4 ~ values range from 3.1 %O to 9.9%0, and reflect the overall isotopic composition of precipitation in West Antarctica during non-eruptive times as well as global volcanic events. There is no apparent change in 6 3 4 ~ due to the sulfate (Sod2') h m a global volcanic event (1963 Agung eruption), indicating that the 6 3 4 ~ is independent of ~ 0 4 ~ - concentration and may not be perturbed by all large eruptions. The 6 3 4 ~ value of each sample represents a combination of ~ 0 4 ~ - with sources including marine biogenic (1 8 to ' 20%0), sea salt (21%0), and volcanic (-O%O). Given the relatively large input of marine aerosols at RIDSA (determined from ~ a ' data and the seasonal SO$ cycle), there is a large marine biogenic SO$ influence. Because the 6 3 4 ~ values from the RlDSA dataset are all well below those predicted for SO:' with a purely marine biogenic source, another SO:- source with low (26 peqlL) to 0.4%0 during times of low SO:- deposition ( 4 peq/L). This relationship illustrates the influence of both dust storms (caused by an increase in vertical convective transport) and anthropogenic inputs on the regional sulfur cycle. Anthropogenic emissions are the source of the background with changes in isotopic signature occurring with dust deposition. Overall, anthropogenic emissions contributed 43% of the ~ 0 4 ~ - while dust sources contributed 57%. These two datasets provide insight into the strengths and limitations of applying sulfur isotopes to ice core studies. 6 3 4 ~ measurements can be used to partition and estimate relative SO:- source contributions in individual samples, and thus provide better estimates of the impact of the sulfur cycle on climate and ecosystems. The isotope ratio mass spectrometer (IRMS) techniques used in this study require large sample volumes (100 pg of S) and thus limit the sample resolution possible in typical ice core locations. New methods of 6 3 4 ~ analysis via inductively coupled plasma mass spectrometry (ICP- MS) show promise, with high (0.09 RSD) precision 6 3 4 ~ analysis with sample concentrations of ~ 0 4 ' - as low as 1 ppb. ICP-MS analysis may allow high-resolution (sub seasonal) ice core data to be routinely produced from remote polar and alpine regions.