HR: 1340h
AN: U43A-0740    [Abstracts]
TI: Centennial to Millennial Scale Variations in the Indian Summer Monsoon Winds and Solar Variability
AU: * Anderson, D M
EM: david.m.anderson@noaa.gov
AF: NOAA Paleoclimatology and INSTAAR, U. of Colorado, 325 Broadway, E/CC23, Boulder, CO 80303 United States
AU: Gupta, A K
EM: anilg@gg.iitkgp.ernet.in
AF: Department of Geology and Geophysics, Indian Institute of Technology , Kharagpur, 721 302 India
AU: Overpeck, J T
EM: jto@u.arizona.edu
AF: Institute for the Study of Planet Earth and Department of Geosciences, University of Arizona, Tuscon, AZ 80303 United States
AB: The monsoon circulation arises from the seasonal variation in the energy received from the sun, and records of the Indian summer monsoon provide a means to understand the sun-climate connection. The Indian summer monsoon wind speed was reconstructed from G. bulloides shell abundance in foraminifer-bearing nannofossil ooze sediments from the NW Arabian Sea for the past 10,000 years. This study extends our previous work by increasing the sample resolution to 50 years, by calibrating the G. bulloides record in terms of alongshore wind stress, and by quantifying the link between Arabian Sea wind speed and other aspects of the monsoon such as all-India rainfall and the surface pressure gradient. Coarse age control relative to solar variations make stratigraphic correlations uncertain. Nevertheless, we found concentrations of variance in the monsoon wind speed at the century to millennial scale that correspond to solar variations indicated by the Be-10 and C-14 proxies. The correlation is strongest in the early Holocene, and weakest during the late Holocene when the monsoon was weak. The Maunder Minimum was a time of reduced solar output and with low seasonality due to the precession of the axis of Earth rotation, and corresponds to the interval of the weakest monsoon winds observed during the last 10,000 years. At the millennial scale, the monsoon winds correspond not only with solar variability but also with times of cooler conditions in the North Atlantic. The hypothesis of a direct solar link to the tropical monsoon circulation versus a connection via the North Atlantic remains unresolved, both explanations supported by conceptual and numerical models.
DE: 4267 Paleoceanography
SC: Union [U]
MN: 2004 AGU Fall Meeting