Large mass-independent sulphur isotope anomalies link stratospheric volcanism to the Late Ordovician mass extinction

Abstract

Volcanic eruptions are thought to be a key driver of rapid climate perturbations over geological time, such as global cooling, global warming, and changes in ocean chemistry. However, identification of stratospheric volcanic eruptions in the geological record and their causal link to the mass extinction events during the past 540 million years remains challenging. Here we report unexpected, large mass-independent sulphur isotopic compositions of pyrite with Δ 33 S of up to 0.91‰ in Late Ordovician sedimentary rocks from South China. The magnitude of the Δ 33 S is similar to that discovered in ice core sulphate originating from stratospheric volcanism. The coincidence between the large Δ 33 S and the first pulse of the Late Ordovician mass extinction about 445 million years ago suggests that stratospheric volcanic eruptions may have contributed to synergetic environmental deteriorations such as prolonged climatic perturbations and oceanic anoxia, related to the mass extinction.

Vertical decoupling in Late Ordovician anoxia due to reorganization of ocean circulation

“…1) -at the beginning of the Hirnantian and near the end of the Hirnantian ('LOME 1' and 'LOME 2', respectively). LOME 1 may be related to habitat loss associated with glacioeustatically-driven sea-level changes or potentially volcanism [2][3][4] , while the drivers responsible for LOME 2 are more debated. In the traditional time-line interpretation, LOME 2 occurred during deglaciation; extinction was then triggered by the expansion of anoxia onto the shelves during the associated sea-level rise 5 .…”

Different controls on the Hg spikes linked the two pulses of the Late Ordovician mass extinction in South China

“…A diagenetic effect is excluded because of the well-preserved conditions of primary laminated shale 4 , 14 . In addition, organic-carbon isotope data record the global positive excursion of the glacial interval in the Hirnantian stage, also suggesting a primary chemostratigraphic signal preserved in the sample containing matured organic matter 52 . These analyses point to no or weak diagenetic effect on our geochemical data across the O–S boundary.…”

“…Elsewhere, one Hg positive anomaly had also been found in late Katian from a drill hole XY5 in South China 23 , 52 and Monitor Range in North America 22 . Two Hg positive anomalies at LOMEI-1 and LOMEI-2 had also been found in many locations such as Wangjiawan, Dingjiapo 21 , XY5 drill hole 52 in South China and Monitor Range section in North America 22 . In other locations in South China, Hg positive anomalies were found in the early Rhuddanian 48 .…”

Thinking beyond the data: When the sea went dark

“…Looking at each of the mass extinction events in turn, the late Ordovician mass extinction, which resulted in the loss around 85% of marine species, has now been identified as being associated with two pulses of extensive volcanism (Bond & Grasby, 2017, 2020; Wang et al., 2019), producing stratospheric‐wide sulphur aerosol (Hu et al., 2020).…”