Lessons from latest global warming
Similar to current and future warming, the Paleocene-Eocene Thermal Maximum (PETM) occurred 56 million years ago and was one of the largest and fastest global warming events in Earth history. Global temperatures increased by 5-8°C during this phase. It was characterized by an increase in the seasonality of rainfall, which resulted in a significant amount of clay being transported into the ocean and becoming unsuitable for various types of living organisms. This situation could now repeat itself.
The Paleocene-Eocene Thermal Maximum (PETM), which occurred 56 million years ago, is the largest and most rapid climatic disturbance of the Cenozoic (65.5 million years ago to present). This episode was exceptional both in terms of its amplitude (5-8°C increase) and its suddenness (5,000 years, a very short time on a geological scale) and was characterized by a warming of temperatures on a global scale. It lasted about 200,000 years and led to numerous marine and terrestrial extinctions. It would have been caused by high concentrations of carbon dioxide – the famous CO2 – and methane in the atmosphere, two powerful greenhouse gases. As is currently the case, these gases may have been released by several phenomena, certainly in combination: the release of methane hydrates trapped on the seabed, the sudden and significant melting of the permafrost and the injection of magma into the organic sediments of the Western edge of Norway. The origin of these processes is still debated. A meteorite impact and/or the effects of intense volcanic activity deep in the North Atlantic could be responsible.
Because of the many similarities between PETM and current warming, the geological remains of this period are being closely studied by scientists. A UNIGE team is now reporting new elements. “The aim of our study was to investigate the influence of these climatic changes on sediment 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 depths of the ocean,” explains Lucas Vimpere, postdoctoral researcher in the Earth and Environmental Sciences Section of UNIGE’s Faculty of Science and first author of the study. The researchers analyzed sediments from more than 8 km deep in the Gulf of Mexico. This basin acts as a huge “sink” into which material eroded and transported from the North American continent is drained over millions of years. “Due to cost and infrastructure reasons, the sediments used to study the PETM are generally from shallow marine or continental environments. Thanks to the collaboration with an oil company, we were able to obtain a sample of unprecedented quality, without any alteration,” said the researcher. The 543 meter long core contains a 180 meter thick PETM sediment record, making it the world’s most complete geological ‘archive’ of this period.
UNIGE scientists found that it consisted first of a large layer of clay and then of sand, a counterintuitive result. “At the time of the PETM, we thought that there was more precipitation and therefore more erosion and that large amounts of sand were then transported first from the river systems into the oceans. But thanks to our sample, we were able to determine that it was primarily the clay and not the sand,” said Sebastien Castelltort, full professor in the Department of Earth and Environmental Sciences at UNIGE’s Faculty of Science and senior author of the study It was found that the period was not marked by an increase in the annual rate of precipitation, but rather by an increase in its seasonality and intensity.”This led to increased mobility of the river channels – the deepest parts of a river – which in turn carried large amounts of river clay, deposited on the adjacent alluvial plains, transported to the ocean depths. We can now consider the presence of clay in deep basins as an indication of increased seasonality in precipitation,” said Lucas Vimpere. The phenomenon has led to an increase in ocean turbidity , which are harmful to marine life, especially corals h is
“The PETM is a potential analogue of current warming. As recent IPCC reports show, we are now also seeing an increase in seasonality and intensity of precipitation. As our study shows, this is likely to destabilize sediment systems in the same way as it did during PETM, and with the same consequences for the oceans and living species,” Vimpere added. This new data can now be integrated into modeling aimed at predicting the evolution and consequences of global warming (ANI)
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