The connection between the large-scale flood basalt volcanic activity and the mass extinction event at the end of the Triassic period (201 million years ago) is widely accepted. However, it is challenging to determine exactly how the volcanic activity led to the breakdown of ecosystems and the extinction of entire groups of organisms. Contributing factors include extreme climate change from the release of carbon dioxide, depletion of the ozone layer from the introduction of harmful chemicals, and the release of toxic pollutants. One particular toxic element that stands out is mercury.
The link between massive flood basalt volcanism and the end-Triassic (201 million years agMass extinction is widely acknowledged, but determining exactly how volcanic activity caused ecosystems to collapse and led to the extinction of entire organism families is challenging. Contributing factors such as extreme climate change from carbon dioxide release, ozone layer degradation from harmful chemical injection, and emissions of toxic pollutants are all considered to have played a role. One particularly noteworthy toxic element is mercury, known as one of the most toxic elements on the planet. Mercury is emitted from volcanoes in gaseous form and has the ability to spread globally. A recent study published in Nature Communications presents compelling new evidence.The team of scientists from the Netherlands, China, Denmark, the UK, and the Czech Republic explored sediments from Northern Germany to investigate the impact of global warming and widespread mercury pollution on plant life. Using a drill-core (Schandelah-1) that covers the uppermost Triassic to lower Jurassic period, they analyzed microfossils and geochemical signals. Their study of pollen and spore abundances revealed an abundance of fern spores with various malformations, including abnormalities in wall structure and signs of unsuccessful meiotic divisions resulting in incomplete separation.arfed, and fused fern spores. “The discovery of a large and diverse collection of deformed fern spores in sediment samples from a coastal lagoon dating back to 201 million years ago is truly remarkable. This suggests that there was a significant amount of stressed ferns during that time,” says Remco Bos, a PhD candidate at Utrecht University and the main researcher behind the study. “This phenomenon is not commonly observed in other periods with abundant fern fossils, making it a distinct indicator of the end-Triassic mass-extinction event.”
Impact of Deforestation on Ferns
The findings of Bos and his co-authors support previous research conducted by their colleagues.Sofie Lindström from the University of Copenhagen, Hamed Sanei from Aarhus University, and Bas van de Schootbrugge from Utrecht University previously collected similar data from cores in Denmark and nearby outcrops in Sweden. According to Lindström, the transition from trees to ferns during the extinction interval was due to significant environmental changes, such as heat stress, increased monsoonal rainfall, and heightened forest fire activity. The palynological results indicate that a pioneering fern vegetation spread across coastal lowlands in Northwestern Europe, spanning from Sweden and Denmark to Germany, France, and Luxembourg.The countries of Luxembourg and Austria are responding to the issue of widespread deforestation. Ferns are resilient plants that often thrive in disturbed environments, such as newly formed volcanic islands or areas affected by volcanism or wildfires. It is remarkable that despite producing deformed spores in various locations, the ferns did not become extinct. While other plant species faced extinction, the ferns demonstrated enough resilience to survive, potentially due to their tolerance to mercury. The study also examines how the ferns took advantage of dieback and climate variability.The study found that even after the mass extinction event, forests were still under stress from high levels of mercury pollution. Four more time intervals were discovered with elevated mercury concentrations and a large number of deformed spores in the 1.3 to 2 million years following the extinction event. This period, known as the Hettangian, continued to bring challenging conditions for marine life, with low diversity among marine invertebrates like ammonites and bivalves. However, on land, vegetation seemed to recover more quickly. The research demonstrates that the forest ecosystem continued to be disturbed repeatedly for at least…Bos explains that the high Hg concentrations and fern spore malformations occurred around 1.3 million years ago, and possibly up to 2 million years ago. The researchers found that these episodes were not linked to later phases of Central Atlantic Magmatic Province volcanism. Instead, they discovered that these periods coincided with the long eccentricity cycle, which is the major variation in the shape of Earth’s orbit. This cycle causes Earth to move closer or further away from the Sun every 405 thousand years. When Earth is at its closest point to the Sun during eccentricity maxima, more sunlight reaches the Earth’s surface. Since the Earth’s atmosphere was already supercharged during this time, the additional sunlight led to the high Hg concentrations and fern spore malformations.The climate system was influenced by large-scale volcanism, causing repetitive forest dieback and the spread of pioneer ferns. There was a correlation between high Hg contents and malformations in fern spores, indicating mercury poisoning. The source of the mercury, however, was unknown.
Wang Zheng, a geochemist from Tianjin University in China, conducted crucial research on Hg-isotopes, providing valuable data on mercury’s different isotopic compositions.The stability of isotopes can vary in the environment. When natural reactions occur, such as the release from volcanic activity, accumulation from the atmosphere, and absorption by living organisms, Hg-isotopes can undergo fractionation. This results in the enrichment of heavier isotopes in one pool and lighter isotopes in others. Sediments with high levels of Hg and deformed spores also display distinct variations in Hg-isotopes. “By analyzing the variations in Hg-isotopes, we were able to connect the initial surge in Hg enrichment at the Triassic-Jurassic boundary to the release of mercury from flood basalt volcanism,” Wang Zheng explains. “However, the four other surges in mercury ha…
“The isotopic composition of the sediments suggests that Hg input from soil erosion and photochemical reduction were the main drivers,” said the researchers.
Impact of Climate Change and Pollution
Overall, the combination of geochemical and microfossil data indicates a more complex and prolonged series of events. This began with significant volcanism causing climate change and the release of toxic pollutants. This was followed by intermittent disturbances in the aftermath of the extinction event, lasting for at least 1.3 million years. Dr. Tomas Navratil from the Czech Academy of Sciences, a co-author of the paper and an expert in modern-day mercury, stated this.The environmental impact of mercury pollution is a concern, as indicated by recent research in the Czech Republic. The study found that polluted sites showed evidence of mercury remobilization from forest soils, particularly during hot summers and in areas with greater sun exposure. This led to the photochemical reduction of mercury and its release into the atmosphere. The researchers noted that mass-extinction events were complex and prolonged, and that a combination of greenhouse warming and pollution contributed to ongoing ecosystem disruption. Coastal ecosystems were particularly affected by the influx of mercury from large catchment areas.The system eventually recovered during the Sinemurian period, when stable forested biomes started to appear. It is likely that by that time, Earth had cleaned up the mess, carbon dioxide levels had decreased, and mercury was permanently buried in offshore marine sediments,” Bos concludes.
Journal Reference:
- Remco Bos, Wang Zheng, Sofie Lindström, Hamed Sanei, Irene Waajen, Isabel M. Fendley, Tamsin A. Mather, Yang Wang, Jan Rohovec, Tomáš Navrátil, Appy Sluijs, Bas van de Schootbrugge. Climate-forced Hg-remobilization associated with fern mutagenesis in the aftermath of the end-Trias rnrnExtinction rates are currently at a critically high level, according to a recent study published in Nature Communications. The study can be found at http://dx.doi.org/10.1038/s41467-024-47922-0.