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Timing of the 74 ka Toba eruption against large climatic change constrained using Borneo stalagmites
Stacy Carolin
Institute of Geology, University of Innsbruck, Austria
Jeudi 20/12/2018, 14h00-15h00
Bât. 701, P. 17C, LSCE Orme des Merisiers

While there is no doubt surrounding the magnitude of the 74 ka Toba super-eruption, its global and regional impact on climate, terrestrial ecosystems, and prehistoric humans remains a topic of heated debate. Notably, both Chinese and Borneo stalagmite oxygen isotope records, proxies for Asian monsoon strength and West Pacific tropical convection, respectively, reveal the start of an ~300yr shift to a 1000yr-long dry period within error of the Ar-Ar dated Toba eruption. It is therefore conceivable that the eruption played a role, whether direct or indirect, in shaping global-scale climate over the following several centuries, not decades, which is in stark contrast to the suggested climate effect provided by climate models. To better constrain the timing of the eruption relative to the climate records, we have performed multiple micro-analytical analyses on several tropical Mulu stalagmites (northern Borneo) with the aim of pinpointing the exact location of eruption chemical signatures within the stalagmite layers. The analyses support our hypothesis that traces of the Toba eruption are preserved in Mulu stalagmites, a site 1100 miles east of the Toba caldera and within the deposited ash zone of this super eruption. We compare the location of the eruption signatures with the oxygen isotope record, both measured within the same stalagmite, to determine the exact timing of the eruption relative to the start of the ~300yr shift to a 1000yr-long regional dry period. Radiometric U/Th ages are used to translate the stalagmite depth scale to age scale.

 

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