Preprints
https://doi.org/10.5194/cp-2021-38
https://doi.org/10.5194/cp-2021-38

  14 Apr 2021

14 Apr 2021

Review status: this preprint is currently under review for the journal CP.

New insights into the ~74 ka Toba eruption from sulfur isotopes of polar ice cores

Laura Crick1, Andrea Burke1, William Hutchison1, Mika Kohno2, Kathryn A. Moore3, Joel Savarino4, Emily A. Doyle5, Sue Mahony6, Sepp Kipfstuhl7, James W. B. Rae1, Robert C. J. Steele1, R. Stephen J. Sparks6, and Eric W. Wolff5 Laura Crick et al.
  • 1School Of Earth And Environmental Sciences, University Of St Andrews, United Kingdom
  • 2Geoscience Center (GZG), Department of Geochemistry, Georg August Universität Göttingen, Germany
  • 3Department Of Atmospheric Science, Colorado State University, USA
  • 4Institut Des Géosciences De L'environnement, Grenoble, France
  • 5Department Of Earth Sciences, University Of Cambridge, United Kingdom
  • 6School Of Earth Sciences, University Of Bristol, United Kingdom
  • 7Alfred-Wegener-Institute, Bremerhaven, Germany

Abstract. The ~74 ka Toba eruption was one of the largest volcanic events of the Quaternary. There is much interest in determining the impact of such a huge event, particularly on the climate and hominid populations at the time. Although the Toba eruption has been identified in both land and marine archives as the Youngest Toba Tuff, its precise place in the ice core record is ambiguous. Multiple volcanic sulfate signals have been identified in both Antarctic and Greenland ice cores within the uncertainty of age estimates as possible events for the Toba eruption. We measure sulfur isotope compositions in Antarctic ice samples at high temporal resolution across 11 of these potential Toba sulfate peaks in two cores to identify candidates with sulfur mass-independent fractionation (S-MIF), indicative of an eruption whose plume reached altitudes at or above the ozone layer in the stratosphere. Using this method, we identify several candidate sulfate peaks that contain stratospheric sulfur. We further narrow down potential candidates based on the isotope signatures by identifying sulfate peaks that are due to a volcanic event at tropical latitudes. In one of these sulfate peaks at 73.67 ka, we find the largest ever reported magnitude of S-MIF in volcanic sulfate in polar ice, with a Δ33S value of −4.75 ‰. As there is a positive correlation between the magnitude of the S-MIF signal recorded in ice cores and eruptive plume height, this could be a likely candidate for the Toba supereruption, with a plume height in excess of 45 km. These results support the 73.7 ± 0.3 ka (1σ) ka Ar/Ar age estimate for the eruption, with ice core ages of our candidates with the largest magnitude S-MIF at 73.67 and 73.74 ka. Finally, since these candidate eruptions occurred on the transition into Greenland Stadial 20, the relative timing suggests that Toba was not the trigger for the large Northern Hemisphere cooling at this time although we cannot rule out an amplifying effect.

Laura Crick et al.

Status: open (until 09 Jun 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review', Anders Svensson, 12 May 2021 reply

Laura Crick et al.

Laura Crick et al.

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Short summary
The ~74 ka eruption of Toba was one of the largest eruptions of the last 100 ka. We have measured the sulfur isotopic composition for 11 Toba eruption candidates in 2 Antarctic ice cores. Sulfur isotopes allow us to distinguish between large eruptions that have erupted material into the stratosphere and smaller ones that reach lower altitudes. Using this we have identified the events most likely to be Toba and place the eruption on the transition into a cold period in the Northern Hemisphere.