Some 90 Million years ago, West Antarctica was a thiving rainforest. Fossil roots, pollen and spores have been found under the ice.

The world was different during the Cretaceous period, from 145 to 66 million years ago. Dinosaurs roamed the planet,  and sea level was sometimes 170 metres higher than today. It was a hot and wet climate, similar to that currently in New Zealand.

The remains of the Antarctic rainforest were discovered under the ice in a sediment core, by an international team of researchers, near Pine Island Glacier in West Antarctic in 2017. The discovery and analysis were carried out by an international team of researchers led by geoscientists from the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research in Germany and including Imperial College London researchers. Their findings have been published in “Nature”.

When the team found the core, they knew they had found something unique. Back in their lab, the team put the core into a scanner. The images showed a dense network of roots throughout the whole soil layer. it also revealed ancient pollen, spores and the remains of flowering plants from the Cretacious Period.

By analysing the pollen and spores, they were able to reconstruct 90 million year old vegetation and climate. The numerous plant remains indicate that the coast of West Antarctica was a dense temperate, swampy forest, similar to the forests found today in New Zealand.The sediment core revealed that the annual mean air temperature was about 12 degrees Celsius, Summers were warmer, with an average of 19C. The water temperature would have reached up to 20C. These temperatures are exceptionally warm, if you realise that the South Pole has a four-month period of polar night: a third of the year there was no sunlight at all.

The studies also showed that the amount of carbon dioxide was higher than expected: it took concentration levels of 1120 to 1680 parts per million of carbon dioxide to reach the average temperatures back then. The assumption before the study was that it would have been around 1000 parts per million. Whether this discovery is good or bad is still open for discussion. It is also not completely clear what caused this huge amount of Carbon Dioxide.

Scientific studies have shown that atmospheric Carbon Dioxide in past eras reached concentrations that were 20 times higher than the current concentration. Recent investigations have shown that the current change of climate is part of a larger cycle known as climatic lowstand phase which precedes a sequential warming period known as transgression phase. The purpose of this evaluation is to demonstrate that the Earth is actually cooling, in the context of the total geological timescale, and that the current change is equivalent to a serial climate phase known as lowstand.

One source for that amount of Carbon Dioxide is Methane Clathrate, which was, and still is, trapped in Antarctic ice. Methane clathrate, also called fire ice or burning ice, is a solid in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice. Originally thought to occur only in the outer regions of the Solar System, where temperatures are low and water ice is common, significant deposits of methane clathrate have been found under sediments on the ocean floors of the Earth.

In 2008, research on Antarctic Vostok and EPICA Dome C ice cores revealed that methane clathrates were also present in deep Antarctic ice cores The ice-core methane clathrate record is a primary source of data for global warming research, along with oxygen and carbon dioxide.