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Issue 468, 4 June 2001

Lost forests and ancient flowers yield clues to climate change

Locked under the frozen wastes of the Antarctic are the fossilised remains of tropical forests, which flourished over fifty million years ago but were lost when the Earth's climate cooled and the polar ice caps were formed. From huge fossilised trunks to tiny specks of charcoal, scientists from Leeds are studying the remains of this ancient habitat. They believe that knowledge of ancient climate changes will bring understanding of the processes of global warming which are now melting the ice and snow of the Antarctic region.

Between a rock and a hard place – Dr Jane Francis with a fossilised tree trunk. Studying the cross-sections shows the kind of climate in which the trees were growing 40 million years ago.

Dr Jane Francis and Dr Anne-Marie Tosolini of Earth Sciences are working in collaboration with the British Antarctic Survey to research the forests. They spend ten weeks at a time on an island off the Antarctic Peninsula, a finger of land pointing towards South America. There, the harsh winds have blown away the ice, snow and soft rock, leaving many fantastically preserved fossils exposed on the hard rock face.

"It's an amazing place to work," explains Dr Francis. "These forests were wiped out forever forty million years ago, and there are no equivalent living forests at such high latitudes today. It's like looking through a window at a lost world."

The researchers have also discovered a seam of charcoal, the result of a forest fire, and amongst the burnt remains have identified the oldest flowers - dating back 80 million years - ever found in Antarctica.

Dr Helena Eklund doesn't brave the ice and snow, but in the lab she painstakingly sifts through this charcoal dust, collected by her colleagues in the Antarctic. The dust is magnified 20,000 times under an electron microscope, and Dr Eklund has managed to identify flowers, seeds, fruit and nuts all from the Cretaceous period, between 140 - 65 million years ago. She explains: "In a forest fire, the heat is so intense that plants are caught in the flames, burnt in an instant and perfectly preserved. For this reason, charcoal seams often display the fossils of 'softer' items such as flowers, seeds and nuts which would usually decay before fossilisation can take place.

Ancient dust – Dr Helena Eklund with a tray of the 80 million year old charcoal which she has been painstakingly searching for the remains of flowers, seeds, nuts, pollen and insects.

"Identification is still very difficult, not only because the specimens are so tiny, but because many flowers are recognised by colour - which fossils don't have. Often the most fragile parts, the petals and stamens are missing, so I only have the central stems to go by. But where fossils are fairly complete, they can be cross-sectioned to see their internal structure which can help with identification."

Dr Eklund uses cell structure in particular to link to modern day equivalents, or species already identified by colleagues working with more substantial trunks and leaves.

"I've not found any insects yet, but I'm still hopeful I might, as some of the flowers I've identified are insect pollinated, so they must have been present at the time," says Dr Eklund. "I've plenty more dust left to work through, so who knows what I might find!"

By any other name – the stem of a fossilised flower, with a diagram showing its reconstruction




Microscopic remains – a fern frond and a seed, caught in the charcoal

Dr Francis' main interest is in trees, and the fossils she studies can at first glance look just like ordinary tree trunks. The only difference is that they are solid rock, not wood. Dr Francis takes these pieces of petrified forest, slices through them with a diamond-edged cutter and then studies the cross-sections under magnification to see the cell structure, rings and general composition, which enable identification and are also markers of climatic conditions.

She said: "We've also collected fantastic leaf fossils, both of trees and ferns. We are now working to identify the different species, by looking at things like size, shape and vein formation, whether or not they have serrated edges. All these things can help match them with modern day equivalents in South America or Tasmania, which at the time were connected by land to the area where they were collected."

On the surface – the harsh winds of the Antarctic blow away surface snow and rock to leave the fossils exposed

Detailed knowledge of the types of plants growing in the region can tell the researchers what kind of conditions prevailed and the findings also show the changes in environment and climate over time. The polar ice caps are the extremes, not just of geography but also of climate. They are the first parts of the world to show the effects of climate change, but are also so large that they have a major effect on the Earth's climate, changing ocean levels and temperature as the ice melts and freezes. Environmentalists and climate specialists are monitoring the changes now, but also looking back at the past to provide answers to the effects of global warming.

"Our world was once a greenhouse. While temperatures at the tropics were probably much as they are today, the Antarctic and Arctic were warm, able to support vegetation and populated with dinosaurs and huge marine reptiles, as well as birds and mammals," said Dr Francis. Around forty million years ago, the climate began to cool and the Antarctic ice cap formed, locking the secrets of the forests into rock and ice. The huge expanses of ice cooled the world still further, later creating the Arctic ice cap. "Understanding this incredible change from forest to frozen waste is crucial for understanding the changes going on in today's climate," she added.

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