Reconstruction of a greenhouse warming period

The Paleocene–Eocene Thermal Maximum (PETM) was a period of climate change that occurred about 56 million years ago. Just like the situation now, there was then a substantial increase in greenhouse gases. A team of researchers from Utrecht University, TU Delft and institutes in Germany and the United States, led by geoscientist Bas van der Meulen, reconstructed the course of the PETM with unparalleled precision. With that, it will be easier for other researchers to answer questions such as how the increase of greenhouse gases arose and how long it took before the natural system recovered. 

‘Climatologically speaking, the PETM is a very important period’, explains Bas van der Meulen. ‘In a relatively short period of time, but slower than at present, temperatures on earth rose considerably. This had major effects on both aquatic and terrestrial life. Improved understanding of processes during the PETM can lead to improved understanding of the current climate change and its potential consequences.’

Van der Meulen conducted research in the Bighorn Basin (Wyoming, United States). ‘Previous studies into the PETM were often based on data from marine deposits. We examined rock formations consisting of river deposits and investigated their stratification and chemical composition in two long sections. As deposition in river plains is on average faster than in seas, more material from the same period is available for study. This can therefore be done at a higher resolution. In addition, investigating rock that formed on the land is important for deciphering evolutionary changes.’

Fossils

Measurements of the stratification and chemical composition of the rock were carried out with unprecedented resolution. Based on variations in the deposits, Van der Meulen and his colleagues managed to reconstruct the duration and course of the PETM. ‘That says something about the rate of climate changes in this period. We then linked our data to an overview of mammal fossil finds.’ This last aspect provides new insights into how evolution proceeded. In that regard, the PETM is particularly interesting because it was in this period that the first primates evolved – our earliest ancestors.

New answers, new questions

The greenhouse warming period of the PETM was followed by a period of recovery. ‘Knowledge about this interval is vital for determining how much carbon the earth can take up and how nature responds in the long term to such an extreme climate change’, concludes Van der Meulen. ‘Our research revealed quite an abrupt return in the chemical values that are considered indicative of the greenhouse climate. However, we also observed that changes in the rocks and fossils occur only partially synchronous with this return. Thus, a greater precision not only provides more answers, but also raises more new questions.’

Article

Bas van der Meulen worked in 2016 as a junior researcher at the Stratigraphy and Palaeontology research group of the Department of Earth Sciences. He is now doing a PhD at the Geomorphology research group of the Department of Physical Geography. Both departments are part of the Faculty of Geosciences of Utrecht University.

His research is published in: Bas van der Meulen, Philip D. Gingerich, Lucas J. Lourens, Niels Meijer, Sjors van Broekhuizen, Sverre van Ginneken, Hemmo A. Abels, ‘Carbon isotope and mammal recovery from extreme greenhouse warming at the Paleocene–Eocene boundary in astronomically-calibrated fluvial strata, Bighorn Basin, Wyoming, USA’, Earth and Planetary Science Letters Volume 534 (2020), 116044.