Once upon a time, there was a swampy rainforest near the bottom of the world. Buried sediment extracted from the seafloor off West Antarctica contains ancient pollen, fossilized roots and other chemical evidence of a diverse forest that flourished millions of years ago, less than a thousand kilometers from the South Pole. The sediment offers the southernmost glimpse yet into just how warm Earth was during the mid-Cretaceous Period, between 92 million and 83 million years ago. By analyzing traces of vegetation in the sediment, researchers reconstructed climate conditions at the site. Average annual temperatures in the forest were about 13° Celsius, with summertime temperatures reaching as high as 20° or 25° C, the team reports in the April 2 Nature. The mid-Cretaceous is known to have been one of the warmest periods on Earth in the last 140 million years, based on analyses of fossils and sediment collected from the seafloor closer to the equator. Atmospheric carbon dioxide levels are thought to have been at least 1,000 parts per million. (Today’s atmospheric carbon dioxide levels average around 407 ppm, the highest in the last 800,000 years.) But for a forest to thrive so far south, even more potent greenhouse conditions must have existed than previously thought, with atmospheric carbon dioxide levels between 1,120 and 1,680 ppm, says marine geologist Johann Klages. “It shows us the extreme potency of carbon dioxide — what carbon dioxide can really do,” says Klages, of the Alfred Wegener Institute in Bremerhaven, Germany. “Even without light for four months, [Antarctica] could still have a temperate climate.” The team retrieved the 30-meter-long core from within the Amundsen Sea Embayment, where today fast-melting Thwaites and Pine Island glaciers drain into the sea (SN: 1/7/20). Even before analyzing the core, Klages says, the researchers knew it was special: The bottom three meters of sediment, corresponding in time to the mid-Cretaceous Period, showed traces of roots. https://www.sciencenews.org/article/rainforest-antarctica-south-pole-roughly-90-million-years-ago Just some of my own comments to add to this article: This would not have been tropical rainforest, but temperate rainforest. Pockets of temperate rainforest exists as far north as northwest Montana, and even up into the interior of British Columbia. This biome also exists in sheltered fjords along the coastal area of Norway. This type of temperate rainforest, so near to the poles, would have a very short active growing season, and a very long winter lasting half the year. The closer you get to the poles, the more extreme difference there is between the summer and winter temperatures. Especially since during the summer half of the year there is constant daylight. They have also found fossil evidence of ferns that once grew on the northern coast of Alaska.
That wouldn't be that unusual. Plants would go into a state of dormancy, just like they do in northern temperate climates over the winter, and most animals would go into hibernation. You can look at the natural ecology in places like the Yukon in Canada, how the animals cope with the harsh conditions. Perhaps some of the animals may have had big eyes like owls to be able to see in the dark or by the light of the moon, or located other animals by sound. Another bit of trivia, places closer to the poles will actually get better (even though it may still not be great) overhead moonlight at night in the half of the year when they get the least sun. It's pretty much the inverse to the angle to the sun. At the north pole, it's pretty much impossible to get any moonlight at night in the summer.
The cycles of "night and day" (in terms of just moonlight) would, during the half of the year when there is no sun, pretty much just be along 4 week cycles. So presumably the animals would go 2 weeks with some light, and then 2 weeks without light. They might have had some interesting adaptations to this.
What about the tectonic plate movements? Perhaps the land in Antartica was at one time located closer to the equator?
That is correct. At that time, Antarctica was about 1000 miles further north, towards the Indian Ocean area. That certainly contributed to the warmer climate there, but the elevated levels of greenhouse gases also contributed.
There were very little land at the South Pole region around 94 million years ago, which is the dominant reason why there was no ice at the pole, but the region was described as COOL Temperate at the time frame. === Late Cretaceous Climate
