HR: 1340h
AN: PP43A-0608    [Abstracts]
TI: Records of Rainfall and ENSO in the South Pacific From Speleothem Growth Bands
AU: * Rasbury, M
EM: rasbu001@bama.ua.edu
AF: The University of Alabama, Department of Geological Sciences, 202 Bevill Building, Tuscaloosa, AL 35487 United States
AU: Aharon, P
EM: aharon@wgs.geo.ua.edu
AF: The University of Alabama, Department of Geological Sciences, 202 Bevill Building, Tuscaloosa, AL 35487 United States
AU: Harry, D
EM: dharry@cnr.colostate.edu
AF: Colorado State University, Department of Geosciences, 322 Natural Resources Building, Fort Collins, CO 80523-1482 United States
AB: Actively growing stalagmites were collected from the Avaiki cave on the island of Niue in the austral winter of 2002 in order to establish the dominant factors controlling the observed variability in the thickness of their annual growth increments. The isolated island is located (19\deg 05' S; 169\deg 50' W) at the SE fringes of the Pacific Warm Water Pool (WWP) and the instrumental records kept on the island since 1905 indicate that annual rainfall variability is directly linked to the incidence of ENSO. The pronounced rainfall seasonality leaves a mark on the stalagmites such that a layer of clear calcite (ca. 250 microns thick) typically forms during the wet monsoon season (December to April, monthly mean rainfall of 307 mm and mean air temperature of 26\deg C) and a thin dark layer of calcite (ca. 150 microns thick) forms during the dry season (May to November, monthly mean rainfall of 84 mm and average air temperature of 24\deg C). The chronology of four stalagmites, spanning a time interval of up to 200 years, was established on the basis of annual couplet counting and verified by AMS radiocarbon dating corrected for dead carbon contribution. Our study shows good agreement between the annual couplet and the historical rainfall records such that periods of extreme rainfall match faster speleothem growth while droughts correspond to slower stalagmite growth. Power spectra analysis of the couplet thickness data exhibits significant periodicities of 17-20, 10-12, 5-8, 3-4 and 2 years that agree well with the periodicities unraveled in the historical rainfall data. The most prominent cycles revealed in the rainfall data of 3-8 years matches the ENSO cycle (3-7 years) suggesting an ENSO control of rainfall in the region. Lower ranked periodicities of 10-15 years may be related to either a solar variability cycle of 11 years or periodic fluctuations in the expanse of the WWP driven by the Pacific Decadal periodicity (PDO). Our results highlight the potential of high resolution growth band records archived in stalagmites to serve as proxies of climate variability on decadal, century and millennial time scales in the South Pacific region.
UR: http://www.geo.ua.edu/asil
DE: 1620 Climate dynamics (3309)
DE: 1650 Solar variability
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting