HR: 14:55h
AN: T33D-06    [Abstracts]
TI: Chinese loess as a paleoenvironmental indicator of tectonics or climate: the role of the Arctic, cold air outbreaks, and lee cyclogenesis?
AU: * roe, g h
EM: gerard@ess.washington.edu
AF: Department of Earth and Space Sciences, box 351510, university of washington, seattle, wa 98195 United States
AU: bitz, c
EM: bitz@apl.washington.edu
AF: applied physics laboratory, university of washington, box 351360, university of washington, seattle, wa 98195 United States
AU: molnar, p
EM: molnar@cires.colorado.edu
AF: CIRES, University of Colorado, Benson Earth Sciences Building, Campus Box 399 University of Colorado at Boulder, boulder, co 80309 United States
AB: The evolution of the Tibetan Plateau is perhaps the archetypal example of using tectonic, erosional, and paleoenvironmental indicators to reconstruct the best possible history of tectonic and topographic development. One key piece of paleoenvironmental evidence is the very significant increase in the deposition of windblown dust in the region around Lanzhou, China, at around 7-8 million years ago. The resulting loess plateau is one of the most important repositories of paleoclimate information in Asia. Previous geological interpretations have suggested that increased loess deposition implies a strengthening of the wintertime atmospheric circulation regime, caused in part by enhanced deflection of the prevailing winds around the topography developing at that time. However, analyses of the controlling factors in the current climate show that dust storms are almost exclusively a springtime phenomenon, and occur during the passage of cold fronts. Moreover, enhanced wintertime circulations actively suppress dust storms, and therefore inhibit loess deposition. Instead, the important environmental controls on dust storms in the region are lee cyclogensis (storm development due to flow over topography), and cold air outbreaks (intrusions of cold air originating far to the north). In the current climate interannual variability of sea-ice extent in the Arctic Ocean is significantly correlated with the occurrence of these cold air outbreaks. Thus the increase in loess deposition resulted from a combination of the development of a springtime reservoir of cold air to the North, consistent with the onset of glaciation in Greenland at around the same time, and topographic development, which generated the weather disturbances necessary for dust storms.
DE: 8109 Continental tectonics--extensional (0905)
DE: 3344 Paleoclimatology
DE: 1620 Climate dynamics (3309)
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting