Antarctica's last forest

The microscopic remains of an Antarctic forest more than 30 million years old is providing important information about global climate operations.

Australian scientists participating in the international Ocean Drilling Program (ODP) have dated the time when the Antarctic changed from a continent covered by vegetation to a frozen land.

Spores and pollen fossils trapped in submerged sediment buried deep beneath the polar sea, provided evidence of the once cool-temperature rainforest that covered the continent between 34 and 37 million years ago. The expedition uncovered information indicating that the vegetation that grew in the coastal plains of Antarctica was akin to the edges of cool-temperature rainforest now found in the highlands of Tasmania.

Although not tall, the stunted scrub of Antarctica's last forest would have been home to a variety of plants including insect-eating plants (sundew) and pine trees that were approximately 3 m high. Samples revealed remnants of Southern Beech (Nothofagus). These are found occurring naturally in Tasmania, New Zealand and New Caledonia, evidence that these islands once joined Antarctica in the super-continent of Godwana. Collected along with the spores were pebbles dropped from the earliest Antarctic icebergs.

The ODP have conducted exhaustive geological detective work to uncover what happened to turn the cool-temperature Antarctic continent into a barren ice world. About 45 million years ago, Australia started to move northward at a rate of approximately 5 cm per year. By 30 million years ago, the Tasmanian land bridge had separated, allowing cold currents to circulate around Antarctica, cutting it off from the warm currents flowing south from the tropics. This created perfect conditions for ice sheets to form. By 15 million years ago, most of Antarctica was a frozen continent buried deep under ice caps. Vegetation vanished, unable to survive the dramatic climate change.

Core samples were collected from rocks located up to 400 m below the seabed, in water 500 m deep in Prydz Bay in the Australian Antarctic Territory.