Tanzania: CO₂ Link to Antarctic Ice Cap Origin

Researchers from Cardiff, Bristol and Texas A&M Universities spent weeks in the African bush in Tanzania with an armed guard to protect them from lions to extract samples of tiny fossils that could reveal CO₂ levels in the atmosphere 34 million years ago. They gathered sediment samples in the Tanzanian village of Stakishari where there are deposits of a particular type of well-preserved microfossils that can reveal past CO₂ levels. The rock samples have shown a strong link between falling CO₂ levels and the formation of Antarctic ice sheets 34 million years ago, underpinning computer climate models that predict both the creation of ice sheets when CO₂ levels fall and the melting of ice caps when CO₂ levels rise. Levels of carbon dioxide, the main greenhouse gas, mysteriously fell during this time in an event called the Eocene-Oligocene climate transition. This was the biggest climate switch since the extinction of the dinosaurs 65 million years ago. The study reconstructed CO₂ levels around this period, showing a dip around the time ice sheets in Antarctica started to form. CO₂ levels were around 750 parts per million, about double current levels. CO₂, being an acidic gas, causes changes in acidity in the ocean, which absorbs large amounts of the gas. This can be picked up through chemistry of microscopic plankton shells that were living in the surface ocean at the time. The evidence from around Antarctica was much harder to find. The ice caps covered everything in Antarctica. The erosion of sediments around Antarctica since the formation of the ice caps has obliterated a lot of the pre-existing evidence that might have been there. The models could be used to predict the melting of the ice. The suggested melting starts around 900 parts per million, a level that could be reached by the end of this century, unless serious emissions cuts were made.

Source: Planet Ark, 15^th September 2009