Sulfate oxygen-17 anomaly in an Oligocene ash bed in mid-North America: Was it the dry fogs?

Authors

Huiming Bao, Louisiana State University
Mark H. Thiemens, University of California - San Diego
David B. Loope, University of Nebraska-LincolnFollow
Xun-Lai Yuan, Nanjing Institute of Geology and Palaeontology

Date of this Version

2003

Citation

Bao, H., M. H. Thiemens, D. B. Loope, and X.-L. Yuan, Sulfate oxygen-17 anomaly in an Oligocene ash bed in mid-North America: Was it the dry fogs?, Geophys. Res. Lett., 30(16), 1843, doi:10.1029/ 2003GL016869, 2003.

Comments

Copyright 2003 by the American Geophysical Union. Used by permission.

Abstract

The oxygen and sulfur isotope compositions of sulfate, particularly the oxygen-17 anomaly, provide clues to the origin of sulfate. We report a variable oxygen-17 anomaly for water- and acid-leached sulfate from an Oligocene volcanic ash bed in the northern High Plains, U.S.A. We find no sulfate O-17 anomaly, however, in freshly collected ashes from recent eruptions around the world. The Oligocene paleoclimatic and sedimentary evidence argues against a hyperarid condition in the High Plains, thus a long-term background atmospheric sulfate accumulation is less likely the origin. Combining sulfur isotope data, we suggest that the anomalous sulfate was associated with volcanic eruptions in the west, but was not directly carried by ash-falls. Extreme dry-fog (sulfate haze) events resulting from tropospheric oxidation of volcanic sulfur gases might provide a viable explanation for the sulfates in the ash bed that carry the oxygen-17 anomaly.