Cretaceous Dinosaurs Lived in Warm and Variable Greenhouse Climate, Study Suggests
Paleoclimatologists have precisely reconstructed monthly sea surface temperatures at around 50 °N latitude from fossil shells of bivalve mollusks that lived during the Campanian (Late Cretaceous epoch) greenhouse period, about 78 million years ago.
“We used to think that when the climate warmed like it did in the Cretaceous period, the time of the dinosaurs, the difference between the seasons would decrease, much like the present-day tropics experience less temperature difference between summer and winter,” said lead author Dr. Niels de Winter, a postdoctoral researcher at Vrije Universiteit Brussel and Utrecht University.
“However, our reconstructions now show that the average temperature did indeed rise, but that the temperature difference between summer and winter remained rather constant. This leads to hotter summers and warmer winters.”
To characterize the climate during the Campanian greenhouse period, Dr. de Winter and colleagues examined well-preserved oyster and rudist shells from the ancient coastal localities of the Kristianstad Basin in southern Sweden.
“Those shells grew in the warm, shallow seas that covered much of Europe at the time,” they explained.
“They recorded monthly variations in their environment and climate, like the rings in a tree.”
Using a ‘clumped isotope’ method, they found that water temperatures in what is now Sweden during the Campanian greenhouse period fluctuated between 15 and 27 degrees Celsius — over 10 degrees Celsius warmer than today.
“It was thought that during the age of the dinosaurs difference between the seasons was small,” Dr. de Winter said.
“We’ve now established that there were greater seasonal differences. With the same temperature average over a year, you end up with a much higher temperature in the summer.”
“Our results therefore suggest that in the mid latitudes, seasonal temperatures will likely rise along with climate warming, while seasonal difference is maintained. This leads to very high summer temperatures,” he added.
“The results bring new insight into the dynamics of a warm climate on a very fine scale, which can be used to improve both climate reconstructions and climate predictions. Moreover, they show that a warmer climate can also have extreme seasons.”
The findings appear in the journal Communications in Earth and Environment.
de Winter et al. 2021. Absolute seasonal temperature estimates from clumped isotopes in bivalve shells suggest warm and variable greenhouse climate. Commun Earth Environ 2, 121; doi: 10.1038/s43247-021-00193-9