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 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.

Global climate disruption and regional climate shelters after the Toba supereruption

“…Estimates of the YTT eruption column height range from 30 to 42 km (2). Based on ash dispersal modeling with modern windfields, Costa et al ( 2) inferred a best-fit altitude of 42 km and a best-fit duration of 15 h. This high plume altitude is consistent with recently reported mass-independent fractionation of sulfur in several candidate YTT layers (69). In most simulations, we therefore distributed SO 2 emissions between 35 and 40 km in the model, spanning 1.9 °S to 13.3 °N and 93.8 °E to 116.2 °E, centered above the Toba caldera.…”

“…The 1257 Samalas eruption in Indonesia released 158 ± 12 Tg SO 2 (63), similar to the lower emissions scenario. Recent ice core-based estimates for several candidate YTT layers range from ∼150 to 350 Tg SO 2, bracketing this lower emissions scenario (69). We recognize that the 2,000 Tg SO 2 scenario may well exceed the actual sulfur release from the YTT eruption.…”

“…The YTT has been correlated with one of the largest sulfur peaks in the GISP2 ice core, representing sulfur loading of 1,100 to 2,200 Tg SO 2 (68); however, this correlation is somewhat circular in that the attribution of the sulfate peak in the ice core is primarily based on the expectation of strong YTT sulfur loading. More recent work has identified several bipolar sulfate peaks in Greenland and Antarctic ice core records in the interval 74.1 to 74.5 ka that are candidates to represent the YTT eruption (46,69). Petrologically, sulfur concentrations in the rhyolitic Toba magma are likely to be lower than in more mafic magmatic systems like that of Mount Pinatubo (21).…”

Magnitude, frequency and climate forcing of global volcanism during the last glacial period as seen in Greenland and Antarctic ice cores (60–9 ka)

“…For the Holocene, a bipolar synchronization of volcanic eruptions was released with the AICC2012 timescale (Veres et al, 2013). Using sulfur isotopes, it has recently become possible to test if sulfate has indeed reached the stratosphere, which is a prerequisite for being globally distributed, as the sulfate undergoes characteristic isotope fractionation in the stratosphere (Burke et al, 2019;Gautier et al, 2018;Crick et al, 2021;Baroni et al, 2008), but these analyses are still scarce for the last glacial period.…”

Magnitude, frequency and climate forcing of global volcanism during the last glacial period as seen in Greenland and Antarctic ice cores (60–9 ka)

“…For the Holocene, a bipolar synchronization of volcanic eruptions was released with the AICC2012 time scale (Veres et al, 2013). It has recently become possible to test if sulfate has indeed reached the stratosphere, which is a prerequisite for being globally distributed, as the sulfate undergoes characteristic isotope fractionation in the stratosphere (Burke et al, 2019;Gautier et al, 2018;Crick et al, 2021;Baroni et al, 2008), but these analyses are still scarce for the Glacial.…”