An international team of researchers has discovered evidence that rainforests once existed in West Antarctica.
The average Cretaceous period of time, from about 115 million to 80 million years ago, is considered the warmest period in the last 140 million years. The sea surface temperature at that time was probably as hot as 35 ° C, and the ocean level was 170 m higher than at present.
In a sedimentary ice core in the Amundsen Sea in West Antarctica in February 2017, researchers discovered preserved Cretaceous forest soil, which included plant pollen and spores, as well as a network of roots.
The core was assembled from the University of Bremen seabed rig near the Pine Island Glacier on the RV Polarstern expedition. These data gave the group the first opportunity to model the West Antarctic climate during the warmest period of the Cretaceous.
“During initial assessments, the unusual color of the sediment layer quickly caught our attention,” said lead author and geologist Dr. Johann Klages.
– He was clearly different from the layers above him. In addition, the first analysis showed that at a depth of 27 to 30 meters under the ocean floor, we found a layer originally formed on land, not in the ocean. ”
The core was subjected to computed tomography, and a dense network of roots was found in the images, which spread throughout the soil layer of fine clay and silt. They were so well preserved that researchers were able to distinguish individual cell structures.
The soil sample also contained traces of pollen and spores from various plants, including the first remnants of flowering plants ever found at these high latitudes in the Antarctic.
“Numerous plant debris indicates that 93-83 million years ago the coast of West Antarctica was a swampy landscape with temperate rainforests – similar to forests that can still be found on, say, South Island of New Zealand,” said the co-author Professor Ulrich Salzman, also a paleoecologist at the University of Northumbria.
“In order to better understand what the climate was like in this warmest phase of the Cretaceous, we first evaluated the climatic conditions in which modern descendants of plants live,” Klades explained. Researchers then searched for the biological and geochemical parameters of temperature and precipitation in the sample.
The results of studies showed that about 90 million years ago there was a temperate climate about 900 km from the South Pole. The average annual air temperature was 12 ° C, which indicates that the temperature at the South Pole in the Cretaceous was only about 2 ° C warmer than the current average temperature in Germany.
Researchers used information on vegetation, temperature, precipitation as target values for climate modeling in the middle of the Cretaceous.
“Prior to our study, the general assumption was that the global concentration of carbon dioxide in the Cretaceous was approximately 1,000 ppm. But in our model experiments, concentration levels of 1,120 to 1,680 ppm were required to reach average temperatures then in the Antarctic,” said co-author Professor Gerrit Lohmann, a climate simulator at the Alfred Wegener Institute of the Helmholtz Center for Polar and Marine Research (AWI).
The study also shows how large amounts of carbon dioxide are greenhouse gases and how important the cooling effects of ice sheets are, especially at present.
-Now we know that in the Cretaceous period without sunlight it would be possible to live four months in a row. But because the carbon dioxide concentration was so high, the climate around the South Pole was nevertheless temperate, without ice mass, “said co-author Dr. Torsten Bickert, a geologist at the Marum Research Center of the University of Bremen.
Meanwhile, Lohmann said that the simulation “has not yet given a satisfactory answer” to the question of what caused the climate to cool off sharply, that ice sheets formed again after a warmer period in Antarctica. Answers to these questions are currently a major challenge for the international climate research community.