History of the Monsoon in Arabia, a Speleothem-based Paleoclimate Study

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This award investigates the use of stalagmites and other speleothems from caves in northern Oman and Yemen as natural archives for information on the nature and cause of variations in the Indian Ocean monsoon system during interglacial and glacial periods of the last 75,000 years. The Indian Ocean Monsoon is an important weather system that affects both natural and managed resources (e.g., through agriculture and fisheries) and hence the economy of one of the most densely populated areas of the world. Two questions guide the research strategy, namely: 1) How did monsoon precipitation vary between interglacial periods? and 2) How does the timing of the monsoon vary with latitude? The research strategy applied combines studies of modern caves and cave waters, Hydrogen isotope analyses of water from fluid inclusions in modern and ancient speleothems, high resolution Oxygen and Carbon stable isotopic analyses of recent and well-dated ancient speleothems, and spectral analyses of the isotopic time series. Stalagmites, deposits of calcium carbonate that are precipitated from groundwaters in caves, will be used to produce high-resolution records of variation in monsoon rainfall. Changes in the intensity of precipitation are recorded in stalagmites as variations in growth rate, thickness of annual growth layers (if present) and in carbon and oxygen stable isotope ratios.Previous work using stalagmites and other speleothems from caves in Oman has shown that they are a rich source of climate information. The results demonstrate repeated pluvial (i.e., wet) periods in southern Arabia during each of the past four interglacial stages in Earth's climate. More detailed study of the early Holocene, at a resolution of approximately 4 years, shows a close correspondence between monsoon rainfall and solar forcing. Study of the past 800 years of the monsoon at annual resolution indicate a connection to the tropical Pacific El Nino-Southern Oscillation (ENSO) system on decadal and interannual timescales.This project is multi-national in scope and involves collaborators in Switzerland, Germany, Oman, and Yemen.