Fine Resolution Analysis of Lake Malawi Sediment Record Shows No Significant Climatic Impacts from the Mount Toba Super-Eruption of ~75ky

Abstract:

Debate over long, and short-term climatic impacts of the Mt. Toba super-eruption circa 75ky is often focused on East Africa. A severe drop in anatomically modern human populations has been hypothesized to be synchronous with a volcanic winter caused by the Toba super-eruption. If the Toba eruption caused a volcanic winter in East Africa, climatologically-sensitive ecosystems, such as Lake Malawi and its immediate watershed should show a direct and observable response in the sediment record. Cooler temperatures would cause a reduction of density contrast between epilimnion and hypolimnion waters, allowing for increased mixing and oxygenation of normally anoxic bottom waters. Enhanced mixing would cause noticeable changes in lake fly and algal communities. Cooler temperatures might also affect precipitation and the fire regime in the surrounding watershed. We analyzed two Lake Malawi cores at the finest practical resolution. Core 2A-10H-2 was analyzed in less than 6-year intervals and core 1C-8H-1 in 7-year intervals surrounding the Youngest Toba Tephra (YTT) for microfaunal abundance and variability, sediment composition, and evidence of changes in the occurrence of fires or watershed precipitation. Our analysis included point counts of diatoms and other algae, lake flies, charcoal, and siliciclastics. Changes in microfossil assemblage, variability, and abundance, as well as sediment composition around the YTT in Core 2A and 1C do not indicate that increased mixing or cooler temperatures occurred in either the central or northern basins of Lake Malawi. Similarly, charcoal counts do not suggest a change in fire regime. Our results indicate that at a subdecadal scale there was no substantial response in Lake Malawi or its immediate watershed to the Mt. Toba super-eruption, in contrast to predictions from the volcanic winter hypothesis.