HOLIVAR2006 Abstracts
High-resolution speleothem records from Soqotra Island, Yemen as a tool for Indian Ocean Monsoon climate reconstruction.
Peter De Geest1, Sophie Verheyden2, Hai Cheng3, Lawrence Edwards3 and Eddy Keppens1
1Vrije Universiteit Brussel, Department of Geology, Pleinlaan 2, 1050 Brussels, Belgium
2Université Libre de Bruxelles, Département des Sciences de la Terre et de l'Environnement (DSTE), Avenue F.D. Roosevelt 50, 1050 Brussels, Belgium
3Minnesota University, Department of Geology and Geophysics, 310 Pillsbury Drive, Minneapolis, MN 55455-0219, USA
Contact: Peter De Geest (Pierre.De.Geest@vub.ac.be)
Soqotra is an arid tropical island in the Indian Ocean, situated between the Horn of Africa and the Arabian Peninsula. Here, the Intertropical Convergence Zone (ITCZ) passes twice each year, resulting in a bi-annual rainy season, known as the Indian Ocean Monsoon system. Huge cave systems occur on the island and contain an important amount of speleothems, an interesting paleoclimatic proxy, since speleothems are datable with the radiometric U-series method. Two sampled speleothems from Hoq (S-STM1) and Casecas Caves (S-STM5) have formed over the last 6 kyr BP and the last 1 kyr BP (TIMS U/Th dating) respectively. δ13C and δ18O measurements were performed at a resolution up to 50μm, corresponding to a time resolution of up to one month. The two sampling locations, 6 km apart, display similar isotopic changes in both speleothems over the last 1000 years. The speleothems also clearly registered seasonal variations, coinciding with the alternation of dark compact layers and white porous layers, present in both stalagmites. These observations suggest that the speleothems reliably registered climatic changes.
To qualify the climatic significance of these records, meteoric waters, vadose waters, cave drip waters, and recently deposited calcite were analysed for their stable isotopic composition in order to understand the controls on the isotopic composition of the present day calcite in the cave.
Peter De Geest is preparing a PhD entitled "Holocene palaeoclimate reconstruction with the use of stable isotopic and geochemical research on speleothems of the island Soqotra (Yemen)" at the Vrije Universiteit Brussel, Belgium, supported by the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen). Since 2000 he organises scientific multidisciplinary expeditions to the Soqotran Archipelago in coordination with Yemeni Ministries. His work is based cave research in general and stalagmite formation in relation with the Monsoon cycles in particular. The aim is to acquire more insights in the forcing factors of the Indian Ocean Monsoon, affecting the live of more than half of our global population.