The Paleocene-Eocene Thermal Maximum (PETM), which resembles current and future warming, occurred 56 million years ago and was one of the largest and fastest global warming events in Earth’s history. Global temperatures increased by 5-8°C during this phase.
It was characterized by an increase in the seasonality of rainfall, which caused the transport of significant amounts of clay into the ocean and became unsuitable for several species of living organisms. This situation may happen again right now.
The Paleocene-Eocene Thermal Maximum (PETM), which occurred 56 million years ago, is the largest and most rapid climatic perturbation of the Cenozoic Era (65.5 million years ago to the present). This episode, exceptional both in its amplitude (an increase of 5-8°C) and in its suddenness (5000 years, a very short time on a geological scale), was marked by warming temperatures on a global scale. It lasted about 200,000 years and led to numerous marine and terrestrial extinctions.
This would be due to the high concentration of carbon dioxide – known as CO2 – and methane in the atmosphere, two powerful greenhouse gases. As it is now, these gases could have been released by several events, certainly in combination: the release of methane hydrates trapped on the sea floor, the sudden and significant melting of permafrost, and the injection of magma into the organic sediments of the sea floor. western edge of Norway. The origin of these processes is still debated. A meteorite impact and/or the effects of intense volcanic activity in the depths of the North Atlantic could be responsible.
Because of the many similarities between the PETM and current warming, the geological remains of this period are being studied in detail by scientists. The team from UNIGE is now reporting new features. “The aim of our study was to investigate the effect of these climate changes on sedimentary systems, i.e. on the processes of sediment formation and deposition, and to understand how these changes could be transmitted from the atmosphere to the deep ocean,” explains Lucas Vimpere, a postdoctoral researcher at the Section of Earth and Life Sciences environment of the Faculty of Science UNIGE and the first author of the study.
Scientists analyzed sediments taken from more than 8 km deep in the Gulf of Mexico. This basin acts as a giant “sink” into which material eroded and transported from the North American continent over millions of years is dumped. “Due to cost and infrastructure, the sediments used to study the PETM are generally obtained from shallow marine or continental environments. Thanks to the cooperation with the oil company, we were able to obtain a sample of unprecedented quality without any changes,” said the researcher. The 543 meter long core contains a 180 meter thick sedimentary record of the PETM, making it the most complete geological ‘archive’ of this period in the world.
The UNIGE scientists found that it consisted first of a large layer of clay and then of a layer of sand, a counterintuitive result. “During the PETM, we thought that there was more rainfall and therefore more erosion, and that a lot of sand was then transported first by fluvial systems into the oceans. However, thanks to our sample, we were able to determine that it was clays and not sands that were transported in the first place,” said Sebastien Castelltort, full professor in the Earth and Environmental Sciences Section of UNIGE’s Faculty of Science. and last author of the study.
This revealed that the period was not marked by an increase in the annual amount of precipitation, but by an increase in its seasonality and intensity. “This resulted in increased mobility of the river channels – the deepest areas of the river – which in turn transported large quantities of fluvial clays deposited on adjacent alluvial plains to the ocean depths. Now we can consider the presence of clay in deep basins as an indicator of increased rainfall seasonality,” said Lucas Vimpere. This phenomenon has led to an increase in ocean turbidity, which is harmful to marine life, especially corals.
“The PETM is a potential analogue of current warming. As recent IPCC reports show, we are now also seeing an increase in the seasonality and intensity of rainfall. As our study shows, this is likely to destabilize sedimentary systems in the same way as during the PETM, with the same consequences for oceans and living species,” Vimpere added.
This new data can now be integrated into modeling aimed at predicting the development and consequences of global warming.
