Geology Club Seminar

The Asian Monsoon system is an important component of the global climate system that plays a major role in the transport of heat and moisture from the tropics to higher latitudes.  Even small variations in the strength and timing of seasonal rainfall can have significant impacts on the billions of people living within the AM domain, yet climate model projections of future regional-scale hydrologic change still remain uncertain.  Paleoclimate records from speleothems have substantially improved our understanding of the timing and mechanisms of past AM variability on orbital to decadal time-scales, but the impact of these variations on regional precipitation patterns remains unclear.  This is due in part to the multitude of potential controls on speleothem oxygen isotope composition, but also to the sparse coverage of the paleoclimate record over certain regions, such as Mainland Southeast Asia. To address this, I will present new multi-proxy speleothem data from northern Laos spanning the last 38,000 years.  We find that oxygen isotope variations are primarily driven by rainout upstream from our study site, whereas the carbon isotope, trace element, radiocarbon, and crystal fabric records reflect local water balance. Our results confirm that rainfall in northern Laos decreased during previously identified last millennium drought events and during weak monsoon periods such as Heinrich Stadial 1.  I will highlight recent evidence that the demise of the Green Sahara at 4-5 ka contributed to widespread drought across the Asian Monsoon region and that solar variability over the last millennium influences speleothem oxygen isotopes, but not local rainfall amount.  Finally, I will show that, consistent with paleoclimate model simulations, Southeast Asia experienced dry conditions during the early Holocene summer insolation maxima, despite the strong Asian Monsoon at that time.  Our multi-proxy results highlight that Asian monsoon strength and regional precipitation in Mainland Southeast Asia do not always co-vary.