Ash from the Toba supereruption in Lake Malawi shows no volcanic winter in East Africa at 75 ka
Edited by Mark H. Thiemens, University of California at San Diego, La Jolla, CA, and approved March 15, 2013 (received for review January 23, 2013)
Letter
June 21, 2013
Abstract
The most explosive volcanic event of the Quaternary was the eruption of Mt. Toba, Sumatra, 75,000 y ago, which produced voluminous ash deposits found across much of the Indian Ocean, Indian Peninsula, and South China Sea. A major climatic downturn observed within the Greenland ice cores has been attributed to the cooling effects of the ash and aerosols ejected during the eruption of the Youngest Toba Tuff (YTT). These events coincided roughly with a hypothesized human genetic bottleneck, when the number of our species in Africa may have been reduced to near extinction. Some have speculated that the demise of early modern humans at that time was due in part to a dramatic climate shift triggered by the supereruption. Others have argued that environmental conditions would not have been so severe to have such an impact on our ancestors, and furthermore, that modern humans may have already expanded beyond Africa by this time. We report an observation of the YTT in Africa, recovered as a cryptotephra layer in Lake Malawi sediments, >7,000 km west of the source volcano. The YTT isochron provides an accurate and precise age estimate for the Lake Malawi paleoclimate record, which revises the chronology of past climatic events in East Africa. The YTT in Lake Malawi is not accompanied by a major change in sediment composition or evidence for substantial temperature change, implying that the eruption did not significantly impact the climate of East Africa and was not the cause of a human genetic bottleneck at that time.
Acknowledgments
We thank V. C. Smith at the University of Oxford for electron probe microanalysis; the coprincipal investigators of the Lake Malawi Drilling Project (C. A. Scholz, A. S. Cohen, and J. King) and other members of the drilling team; A. Noren and A. Myrbo (LacCore) for assistance with sampling; T. Shanahan for producing a thin section of the Toba interval; A. Lingwall and E. T. Brown for assistance with scanning XRF; J. Halbur for TEX86 analyses; and B. Bandli for SEM images. A. S. Cohen and A. M. Pollard provided useful suggestions for improvement of the manuscript. This research was funded in part by National Science Foundation Grant EAR 0902714 (to T.C.J.) and by the Leverhulme Trust (C.S.L.).
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Cover image: Pictured is an antenna from a female Anopheles gambiae mosquito, revealing surface microstructures called sensilla that contain olfactory neurons. David C. Rinker et al. report that, following a bloodmeal, the expression of genes that modulate odor sensitivity in the antenna fluctuates in a coordinated fashion, coinciding with a behavioral shift from host-seeking to egg-laying. The findings provide insight into the biological basis of odor-sensitive behaviors central to disease transmission. See the article by Rinker et al. on pages 8260–8265. Image courtesy of R. Jason Pitts.
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Submission history
Published online: April 29, 2013
Published in issue: May 14, 2013
Acknowledgments
We thank V. C. Smith at the University of Oxford for electron probe microanalysis; the coprincipal investigators of the Lake Malawi Drilling Project (C. A. Scholz, A. S. Cohen, and J. King) and other members of the drilling team; A. Noren and A. Myrbo (LacCore) for assistance with sampling; T. Shanahan for producing a thin section of the Toba interval; A. Lingwall and E. T. Brown for assistance with scanning XRF; J. Halbur for TEX86 analyses; and B. Bandli for SEM images. A. S. Cohen and A. M. Pollard provided useful suggestions for improvement of the manuscript. This research was funded in part by National Science Foundation Grant EAR 0902714 (to T.C.J.) and by the Leverhulme Trust (C.S.L.).
Notes
This article is a PNAS Direct Submission.
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The authors declare no conflict of interest.
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