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The Toba eruption ∼74,000 y ago was the largest volcanic eruption since the start of the Pleistocene and represents an important test case for understanding the effects of large explosive eruptions on climate and ecosystems. However, the magnitude and repercussions of climatic changes driven by the eruption are strongly debated. High-resolution paleoclimate and archaeological records from Africa find little evidence for the disruption of climate or human activity in the wake of the eruption in contrast with a controversial link with a bottleneck in human evolution and climate model simulations predicting strong volcanic cooling for up to a decade after a Toba-scale eruption. Here, we use a large ensemble of high-resolution Community Earth System Model (CESM1.3) simulations to reconcile climate model predictions with paleoclimate records, accounting for uncertainties in the magnitude of Toba sulfur emissions with high and low emission scenarios. We find a near-zero probability of annual mean surface temperature anomalies exceeding 4 °C in most of Africa in contrast with near 100% probabilities of cooling this severe in Asia and North America for the high sulfur emission case. The likelihood of strong decreases in precipitation is low in most of Africa. Therefore, even Toba sulfur release at the upper range of plausible estimates remains consistent with the muted response in Africa indicated by paleoclimate proxies. Our results provide a probabilistic view of the uneven patterns of volcanic climate disruption during a crucial interval in human evolution, with implications for understanding the range of environmental impacts from past and future supereruptions.
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Discovery of the Youngest Toba Tuff in South Africa; Challenges of Extremely Low Abundance Cryptotephra
The 74 ka Youngest Toba Tuff (YTT) was discovered as cryptotephra in South African archaeological sites at Pinnacle Point (PP) 5-6N, Vleesbaai [1] and Klasies River on the Indian Ocean, and the Diepkloof Rock Shelter on the Atlantic coast nearly 750 km west of PP. The YTT eruption distributed tephra across eastern and southern Africa and provides a widespread isochron useful for dating archaeological deposits, testing age models, and precisely determining the timing of changes in human behavior. At PP, we demonstrated that the MIS 4-5 transition began just before the YTT eruption. Humans thrived both through the YTT event and the changing climate, and important changes in technology occurred just after the Toba eruption [1]. Controversy related to trapped charge age models at the Diepkloof rock shelter [2,3] were resolved by identifying YTT at a location in the stratigraphic section that confirmed the Jacobs et al. [2] model for the site, confirming that technological changes similar to those observed at PP occurred synchronously to those at Diepkloof, not substantially before as suggested by a prior published age model [3]. Processing samples with very low abundance cryptotephra, such as that found in South Africa, is a challenge and requires revision of standard laboratory techniques. Samples with high organic or clay content benefit by being treated with 10% HCl and 3% hydrogen peroxide (H2O2). This step does not degrade shard integrity or affect chemistry and is useful in separating shards from clay and organic particles allowing better recovery in heavy liquids. We also modified the heavy liquid density range from 1.95 - 2.55 to 2.2 - 2.5 g/cm3 to more effectively remove quartz and feldspar as well as biogenic silica. This density range captures shards ranging from rhyolite to dacite in composition. [1] Smith, E. I. et al. Nature 555, 511, 2018 [2] Jacobs, Z. & Roberts, R. G. Journal of Archaeological Science 63, 175-192, 2015. [3] Tribolo, C. et al. Journal of Archaeological Science 40, 3401-3411 2013.
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- Award ID(s):
- 1917173
- PAR ID:
- 10278334
- Date Published:
- Journal Name:
- Annual VM Goldschmidt Conference
- ISSN:
- 1945-7022
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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