Sulfur incorporation, preservation

Sulfur Incorporation. It is also possible for unsaturated and polyunsaturated lipids to survive in sediments by intra- or inter-molecular incorporation of sulfur (75, 34). The wide variety of organo-sulfur compounds (OSC) recognized in sediments in recent years (34,35) demonstrates the viability and prevalence of such reactions. The structures of OSC and the inferred sites of sulfur incorporation demonstrate that this process preserves molecular characteristics that would otherwise be expected to be lost by degradation. For example, specific OSC derive from and retain the structural features of carotenoids and other polyunsaturated isopentenoids (34,55). 

The volcanoes in the Transantarctic Mountains and in Marie Byrd Land of West Antarctica erupted lava flows and pyroclastic ash that was deposited on the surface of the ice sheets. The ash was subsequently buried by snow and was thereby incorporated into the ice. The resulting ash layers now serve a useful purpose in the study of the ice sheets because they are unique event horizons whose age can be determined by isotopic methods (e.g., Folco et al. 2007). In addition, these horizons have preserved a record of the deformation of the ice sheets that is revealed by mapping their outcrop patterns on the bare-ice surfaces in the ablation zones. The chemical composition of the ash has been used to identify the volcanoes from which certain ash layers were erupted, while the sulfate concentration and the acidity (pH) of the ice above an ash layer provide clues to the amount of sulfuric acid that was injected into the stratosphere (Palais 1985). The volcanic dust and sulfuric acid in the stratosphere can cause temporary cooling of the global climate as demonstrated by the eruptions of Krakatau (Indonesia) in 1883, Mount St. Helens (Washington) in 1980, El Chichon (Mexico) in 1982, and Mount Pinatubo (Philippines) in 1992 (Holland and Petersen 1995 Thompson and Mosley-Thompson 1981 Kyle et al. 1981 Self etal. 1981). 

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