# Mercury and isotope data tie Ordovician cooling over ~25 Myr to volcanism before the Hirnantian Glaciation

- Published: 2026-11-15 18:53 UTC
- Section: Planet › Earth sciences
- Tags: Ordovician cooling, Hirnantian Glaciation, large igneous provinces, mercury geochemistry, conodont oxygen isotopes, strontium isotopes, basalt weathering, Late Ordovician Mass Extinction, Yichang sections
- URL: https://realtech.media/news/rt-d4e98e0d2f3a5ed127437059_mercury_and_isotope/

**Paired mercury, oxygen and strontium isotope records from sections near Yichang show cooling from ~470 to ~445 Ma, which the authors link to continental large igneous provinces.**

![Mercury and isotope data tie Ordovician cooling over ~25 Myr to volcanism before the Hirnantian Glaciation](https://realtech.media/media/2026/11/627f30c1236a2c88.png)
*nature.com*

A team has published new and compiled records of volcanic activity, sea-surface temperature and chemical weathering for the Ordovician, according to a paper on nature.com [1]. The data document a ~25-Myr interval of climatic cooling (~470–445 Ma). It began around the onset of the Middle Ordovician, intensified in the Late Ordovician and culminated in the Hirnantian Glaciation [1]. The authors report that the relationships favor volcanism, specifically continental large igneous provinces, as the primary driver of the contemporaneous environmental and climatic changes [1].

## Mercury, oxygen and strontium records

The study uses three biostratigraphically well-constrained marine sections near Yichang City: Huanghuachang, Chenjiahe and Wangjiawan, all less than 15 km apart. Huanghuachang is the stratotype of the Lower/Middle Ordovician boundary, and Wangjiawan is the stratotype for the base of the Hirnantian Stage [1].

Volcanic activity was traced with mercury chemistry: the Hg/TOC ratio and Hg isotopes. Volcanism is the principal natural source of mercury, which stays in the atmosphere for about 1–2 years and can be carried far before deposition. Positive Hg/TOC anomalies signal volcanic input, and emissions from subaerial volcanoes typically show near-zero mass-independent fractionation [1]. Temperature came from oxygen isotopes in conodont bioapatite, and weathering intensity from strontium isotopes in the same material. The time frame rests on published biostratigraphy and newly generated carbonate carbon isotope data [1].

## What the cooling coincided with

According to the authors, cooling went together with long-term intensified weathering of volcanic rock (basalt) and a drawdown of atmospheric pCO2. It also coincided with episodic euxinia in the marine photic zone, during and after major volcanic episodes [1].

The work addresses a gap. Earlier conodont data tied the Great Ordovician Biodiversification Event to cooling of about 10 °C, but the trigger remained contentious. Volcanism had been proposed as the cause of the long-term cooling, yet integrated volcanic and paleotemperature records were lacking to test it [1].

The period spans 485.4–443.8 Ma. Marine invertebrate species and genera increased by about 6 and 3 times during the biodiversification event. The Late Ordovician Mass Extinction, with a ~70–80% species-level extinction rate, occurred in two phases tied to the Hirnantian Glaciation [1]. The authors conclude that the results point to complex modulation of life–environment coevolution during the Ordovician [1].

## Sources

1. [nature.com](https://www.nature.com/articles/s41467-025-66316-4)
2. [scinexx](https://www.scinexx.de/news/geowissen/vulkane-haben-vor-450-millionen-jahren-eine-eiszeit-ausgeloest)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-d4e98e0d2f3a5ed127437059_mercury_and_isotope/