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

Abstract

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 large 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. Several volcanic sulfate signals have been identified in both Antarctic and Greenland ice cores and span the Toba eruption 40Ar/39Ar age uncertainty. Here, we measure sulfur isotope compositions in Antarctic ice samples from the Dome C (EDC) and Dronning Maud Land (EDML) ice cores at high temporal resolution across 11 of these potential Toba sulfate peaks to identify candidates with sulfur mass-independent fractionation (S-MIF), indicative of an eruption whose plume reached altitudes at or above the stratospheric ozone layer. 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 super-eruption, with a plume top height in excess of 45 km. These results support the 73.7±0.3 ka (1σ) 40Ar/39Ar 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.

When Eastern India Oscillated Between Desert Versus Savannah‐Dominated Vegetation

“…The event at the GI/GS 19 transition detected at Site U1446 (Figure 3) correlates well with a severe shift in the Indian hydroclimate (Black et al., 2021). The large explosive eruption of the Toba volcano ∼74 ka (Crick et al., 2021) has been invoked as a cause for this major drying event in India, despite the moderate cooling recorded in the North Atlantic (Kindler et al., 2014) and muted signal of positive Westerlies anomaly in the Arabian Sea (Figure 3; Deplazes et al., 2014). Large northern hemisphere volcanic eruptions can generate a global southward shift of the ITCZ by increasing atmospheric aerosol concentration (Ridley et al., 2015) and therefore reduce the ISM rainfall.…”

Canadian forest fires, Icelandic volcanoes and increased local dust observed in six shallow Greenland firn cores

“…We also emphasize our dating was restricted to use mainly H 2 O 2 and Ca 2+ , and thus we have not made any volcanic matching between the records as part of the dating. We also note that other markers are more specific to volcanic eruptions than the ones used in this study, e.g., non-sea-salt sulfate or sulfur isotopes (Severi et al, 2012;Sigl et al, 2016a;Mayewski et al, 1990;Lin et al, 2022;Crick et al, 2021).…”

Lunar eclipses illuminate timing and climate impact of medieval volcanism

“…We thus assume that lunar eclipses of reddish or coppery colour (that is, with an L value >1) observed in the aftermath of HMP eruptions indicate that aerosol veils were mainly confined to the troposphere and probably had limited climatic impacts. The robustness of our approach was assessed by comparing our results with sulfur isotope records (Δ 33 S) from Dome C (Antarctica) 3 , which have proven a valuable proxy to distinguish between eruptions whose plumes reached the stratosphere at or above the ozone layer and those that remained below 3 , 102 – 107 .…”