During the late Triassic 234 to 232 million years ago, the world’s climate and ecosystem changed dramatically: temperatures and humidity rose, rainfall increased, and the dinosaurs began to spread. A new study now shows that large volcanic eruptions likely formed the basis for these changes. Through four episodes of strong volcanic activity, the CO2 content in the atmosphere rose sharply and not only caused corresponding climate changes, but also caused upheavals in the species composition.
In the Carnian, a period of around seven million years in the Upper Triassic, there was a phase with particularly intense precipitation, the Carnic Pluvial episode, 234 to 232 million years ago. The temperature and humidity rose sharply during this phase, which had serious effects on the flora and fauna. Among other things, the conifers emerged and the dinosaurs spread at this time. It was already known that the Carnic Pluvial episode was marked by large volcanic eruptions. However, it has not yet been possible to establish causal relationships.
Searching for traces in the sediment
A team led by Jing Lu from the Chinese University of Mining and Technology in Beijing has now used sediment analyzes of a lake in northern China’s Jiyuan Basin to track the volcanic activity during the Carnic Pluvial episode and show how the volcanic eruptions contributed to the climate, flora and fauna to change. Lu and his colleagues examined the chemical composition of various sediment layers and also analyzed the spores and pollen in these sediment layers.
The chemical analyzes showed that in some layers in the sediment of the lake an increased amount of mercury is accumulated – a typical sign of deposits after volcanic eruptions. The distribution of mercury, combined with the total mass and composition of organic carbon in the respective layers, suggests that there were four distinct phases with strong volcanic activity. This not only led to mercury deposits, but also to increased carbon input and deepening of the lake as a result of increased precipitation.
Volcanism on a global scale
The researchers assume that the volcanic eruptions that left their mark on the lake’s sediment were global in scope. “While it is possible that there is a local volcanic source for the mercury found, it is likely that the mercury accumulation came from a larger volcanic source that was able to affect the global carbon cycle,” they write . The researchers see the igneous Greater Province of Wrangellia in western North America as the most likely source. Geological findings from other regions of the world also fit in with this.
According to the results, each phase of volcanic eruptions was associated with major disruptions to the global carbon cycle: each eruption released large amounts of CO2 into the atmosphere. In the examined lake, this led to an increased nutrient input and a falling oxygen content. Many aquatic animals could not survive under these conditions. At the same time, CO2 drove global warming and created warmer, more humid conditions – and thus new ecological niches on land.
New animals and plants
“Our results show that large volcanic eruptions can occur in multiple, discrete pulses, underscoring their ability to change the global carbon cycle, disrupt the climate and water balance, and fuel evolutionary processes,” says co-author Sarah Greene of Birmingham University. Her colleague Jason Hilton sums it up: “Within two million years, the world’s fauna and flora have changed fundamentally, including selective marine extinction and the diversification of plant and animal groups on land. Our research shows that this period can be divided into four different events, each triggered by distinct impulses of strong volcanic activity combined with enormous releases of carbon dioxide into the atmosphere. “
His colleague Emma Dunne, who was not involved in the study, added: “This relatively long period of volcanic activity and environmental changes had significant consequences for the animals on land. At that time, the dinosaurs had just begun to diversify, and it is likely that without this event they would never have achieved the ecological dominance they would have over the next 150 million years. “
Source: Jing Lu (China University of Mining and Technology, Beijing) et al., Proceedings of the National Academy of Sciences, doi: 10.1073 / pnas.2109895118