HR: 1340h
AN: PP43A-0611    [Abstracts]
TI: High-Resolution Speleothem Records of the Indian Ocean Monsoon Variability of the Last 6 ka and 0,5 ka From Soqotra Island, Yemen
AU: * De Geest, P
EM: Pierre.De.Geest@vub.ac.be
AF: Vrije Universiteit Brussel, Department of Geology, Scientific Research Worker, Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen) Pierre.De.Geest@vub.ac.be , Pleinlaan 2, Brussels, 1050 Belgium
AU: Verheyden, S
EM: Sophie.Verheyden@fpms.ac.be
AF: Facult‚ Polytechnique de Mons, Service de G‚ologie Fondamentale et Appliqu‚e, Scientific Research Worker, National Fund for Scientific Research, Belgium , Rue de Houdain 9, Mons, 7000 Belgium
AU: Cheng, H
EM: cheng021@umn.edu
AF: Minnesota University, Department of Geology and Geophysics, 310 Pillsbury Drive SE, Minneapolis, MN 55455-0219 United States
AU: Edwards, L R
EM: edwar001@umn.edu
AF: Minnesota University, Department of Geology and Geophysics, 310 Pillsbury Drive SE, Minneapolis, MN 55455-0219 United States
AU: Keppens, E
EM: ekeppens@vub.ac.be
AF: Vrije Universiteit Brussel, Department of Geology, Pleinlaan 2, Brussels, 1050 Belgium
AB: Soqotra is an arid tropical island in the Indian Ocean, situated between the Horn of Africa and the Arabian Peninsula. The inter-tropical convergence zone (ITCZ) passes there twice each year, resulting in a bi-annual rainy season. High-resolution \delta$^{18}$O and \delta$^{13}$C ratios of speleothems from two different caves are used to reconstruct changes in the Monsoon intensity and/or variability. Based on 10 TIMS $^{234}$U/$^{230}$Th dating, two active speleothems from Hoq (S-STM1) and Kazekas Caves (S-STM5) have formed over a period of 6 ka BP and 0,5 ka BP, respectively. To obtain a detailed climate reconstruction more than 1000 \delta$^{13}$C and \delta$^{18}$O measurements were carried out, providing a time resolution between 2,5 and 10 years. In S-STM1 \delta$^{18}$O -values range between -4,5\permil and -1,5\permil and \delta$^{13}$C -values between -10,5\permil and -5,5\permil; while for S-STM5 these values range respectively between -4\permil and -2\permil and -7\permil and -3\permil (vs VPDB). Based on the comparison between \delta$^{18}$O excursions and historical meteorological data, the amount of precipitation is reflected in the \delta$^{18}$O signal. Different mechanisms for the \delta$^{13}$C are considered, such as a diminution of the C$_{4}$-type vegetation during droughts, resulting in more positive \delta$^{13}$C -value or kinetic effects during the calcification process itself. Throughout the time series, co-variation occur between \delta$^{13}$C and \delta$^{18}$O -values (R$^{2}$= 0,69) exhibiting long term (millennial) and short term (decadal) variations. In both stalagmites, layers of white porous calcite (WPC) (0,1-0,5mm) and dark dense calcite (DDC) (0,01-0,1mm) alternate, most probably due to seasonal variations. The WPC has more positive \delta$^{13}$C and \delta$^{18}$O -values, while the DDC shows more negative values, clearly demonstrated by high-resolution micro sampling up to a monthly to bi-weekly resolution. A positive correlation between the greyscale variations in the calcite fabric, the presumably annual growth banding and the inverse stable isotope ratios records support this hypothesis. During dry periods, less precipitation enters the cave-system, resulting in a whitish porous calcite deposition, thinner annual banding and more negative stable isotope ratios and vice versa. To better understand the climatic significance of these records, adapted Environmental Data Acquisition Systems (EDAS) are installed in and near Hoq Cave to obtain information on the actual transfer functions between climate and the proxy data in our speleothems.
DE: 9340 Indian Ocean
DE: 3344 Paleoclimatology
DE: 1040 Isotopic composition/chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting