Strontium Isotopes Reveal Long-Term Drying of the Chinese Loess Plateau Well Before the Toba Super-Eruption

The Youngest Toba Tuff (YTT) super-eruption ~74 kyr BP (VEI 8.8) was the largest volcanic event of the Quaternary, estimated to have erupted 2800 km³ of magma. The ash cloud ejected by the YTT impacted insolation and atmospheric processes including the East Asian Summer Monsoon (EASM). The EASM is a major moisture source for continental Asia, including the Chinese Loess Plateau (CLP). The YTT eruption has also been associated with a shift into the cooler, drier climate of Greenland Stadial 20.

Highly resolved and well dated palaeoclimate records that could help elucidate the impact of the YTT eruption on the hydroclimate of the CLP are lacking. Using a 10,000-year-long strontium isotope record (obtained via LA-ICP-MS) from a stalagmite from the southeastern CLP we reconstruct regional aridity at very high resolution (~5 years).

Strontium isotope ratios reflect the mixing of two distinct strontium sources: loess, representing atmospheric dust input; and local limestone bedrock, the weathering of which is controlled by hydrological dynamics. These two sources can be linked to regional hydroclimate as contributions from loess increase when the region is dustier and generally drier, while wetter conditions would result in an increased contribution from the host rock above the cave. The speleothem strontium isotope record indicates a prominent shift from a more humid to more arid climate, which began to take effect ~1000 years before the YTT eruption. Thus, this local climatic shift could not have been triggered by the volcanic event but related to a longer-term weakening in the EASM (beginning ~75 kyr BP).

Our reconstruction shows that regional climate had shifted to increasingly arid conditions well before the YTT eruption. Our data further suggests that the impact of the YTT eruption on regional hydrological conditions was limited and that the EASM was not greatly impacted over a long time period.