Must be written in the history of the earth new? An international research team led by geoscientists at the Alfred-Wegener-Institute, Helmholtz centre for Polar and marine research (AWI) opened a new, unique window in the early Antarctica. A jungle in the ice.
In a sediment core, the researchers in February 2017 in the West Antarctic Amundsen sea have recovered well-preserved forest floor from the Cretaceous, including many plants, pollen and spores. Also dense root network was there.
The vegetation remains show that about 90 million years ago, a moderate, swampy rain forest in the coastal area of the West grew in Antarctica. The average annual temperature of about 12 degrees Celsius – a for the the southern area of exceptionally warm climate.
sea level is 170 meters higher
This surprisingly high value was, according to the scientists, only possible because of the Antarctic ice sheet was absent at the time, and the concentration of carbon Dioxide in the atmosphere was much higher, as the climate of this modelling were as yet suspect.
The middle Cretaceous period, about 115 to 80 million years ago, is not only regarded as the age of the dinosaurs, it was also the warmest period of the past 140 million years. According to the current state of knowledge, the sea surface temperature in the tropics at that time around 35 degrees Celsius. The sea level was 170 meters higher than today.
In the sediment core they found traces of well-preserved forest-floor © Public Domain Float magazine
Largely unknown, however, how the environment looked to be made of conditions at that time, to the South of the former Arctic circle. From the Antarctic and until now, there was hardly any meaningful climate archives that go back so far.
forest soil from the Cretaceous period,
The new core features, the scientists have now, for the first time the opportunity to reconstruct, on the basis of the unique traces of the West Antarctic climate of the middle Cretaceous period. On a Polarstern Expedition, the researchers are using the Bremen sea floor drill rig MARUM-MeBo70 were able to pull out in front of the Pine Island glacier, a core with remarkable content: It contained almost the original forest soil from the Cretaceous period.
“During the first inspection on Board to the unusual coloring of this layer of sediment fell on us immediately. They differed considerably from the deposits about it. Preliminary analyses revealed also suspect that we had encountered at a depth of 27 to 30 meters under the sea floor in a layer that had to have once formed Land and not in the sea,“ reported first author Dr. Johann Klages, geologist at AWI.
What must it be for the trees to have been: The CT-images show a dense network of roots © Public Domain Float magazine traces of flowering plants
What a unique climate archive of the researchers, however, actually had recovered, revealed only when the sediment core tomography in a computer (CT) was investigated. The CT scan showed a dense network of roots, which moved through the entire soil layer of very fine-grained clay and Silt, and so well preserved that scientists were able to detect single woody Cell structures.
The soil sample also contained a countless number of Pollen and spores of various vascular plants, including even traces of the first flowering plants within the high Antarctic Latitudes. “Many of the plant Remains suggests that the coastal area of the West formed Antarctica from 93 to 83 million years ago, a swamp, and moor landscape, in a temperate rain forest, grew up with a lot of conifers and tree ferns, as it is found today, for example, still on the South island of new Zealand,” says co-author Prof. Ulrich Salzmann, Paläoökologe at Northumbria University in Newcastle, England upon Tyne.
Plant spores under the microscope, © Public Domain Float magazine growth in spite of the polar night
the results of The vegetation analysis, the researchers noted a bit of a puzzle: Under what climate conditions at that time could grow to a latitude of about 82 degrees South, a temperate rain forest? The Antarctic continent was, of course, already in the Cretaceous period at the South pole. That is, in the Region from which the forest floor comes, reigned for more than four months of polar night.
energy-giving light of the sun was missing so a third of the year. “To get a more accurate idea of the climate of this warmest Phase of the Cretaceous period, we investigated, first, under what climate conditions the today living Relatives of that plant exist,” says Johann Klages. Then the scientists searched the forest floor to biological and geochemical temperature and precipitation indicators, on the Basis of which they were able to reconstruct the air and water temperature of the West Antarctic Cretaceous rain forest, as well as the amount of rain.
Many analyses, one result is that The Antarctic was in the Cretaceous ice-free and extremely warm. The results of many different analyses fit together like pieces of a puzzle together: about 90 million years Ago, only about 900 km from the South pole prevailed in a temperate climate.
Warmer than currently in Europe
about 12 degrees Celsius, The air temperature in the annual average. That is to say, the Cretaceous was in the southern region of about two degrees warmer than currently in Germany. The summer in the southern region were on average around 19 degrees Celsius; the temperature of the water of the rivers and swamps, rising to values around 20 degrees Celsius.
This new vegetation, temperature and precipitation data from the West Antarctic the researchers used subsequently as the target for simulations of the climate of the middle chalk in a climate model.
your calculations with a paleo-climate model resulted in the following conditions: The Antarctic continent had to be covered by a dense Vegetation, and no country was allowed to enter in the South polar region, ice shelves the size of the ice sheet and the concentration of carbon Dioxide in the atmosphere was apparently much higher than was previously assumed for the Cretaceous period.
Tropical rain forest – was the Antarctic prior to 90 million years? © Public Domain Float magazine ice sheet cools enormous
“Until our study, it was assumed that the global concentration of carbon Dioxide in the age of the chalk was about 1000 ppm. In our model try to concentration values from 1120 to 1680 ppm were necessary in order to achieve the former, temperatures in the Antarctic,“ says co-author and AWI-climate Modeler Prof. Dr. Gerrit Lohmann.
The study shows, therefore, the magnitude of the impact force has the greenhouse gas carbon dioxide and the importance of the cooling property today’s ice sheets exert. “We know now that the sun was no absence of radiation in the Cretaceous quiet for four months. In the case of a correspondingly high concentration of carbon Dioxide in a temperate climate with no ice at the South pole there was also,“ explains co-author Dr. Torsten Bickert, a geoscientist at the center for Marine environmental Sciences, Bremen University (MARUM).
Why cooled the climate?
The big question is now: If it could be in the Antarctic as warm, which has then led to the fact that the climate cooled strongly, and ice sheets formed? “In our climate simulations, we could find no satisfactory answer,” says Gerrit Lohmann. To find the causes of such tipping points, it is now the task and challenge of international climate research.
the research project, but in particular the Polarstern-Expedition PS104, was Financed by funds from the AWI, the MARUM, of the British Antarctic Survey and the British International Ocean Discovery Program (UK-IODP).
The study is published under the following original title in the journal NATURE: Klages, J. P. et al., “Temperate rainforests near the South Pole during peak Cretaceous warmth”, Nature, 1. April 2020, DOI: 10.1038/s41586-020-2148-5
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