Carbon dioxide spike linked to Antarctic ice melt

Researchers from Columbia University have expressed long term concerns about the mass of the Antarctic Ice Sheet, after seeing how it rapidly shrunk due to a CO₂ spike in the past.

Twenty-three million years ago the Ice Sheet shrunk from a mass 125% larger than its present-day size to half of what exists. Researchers are concerned about the stability of this ice mass as carbon dioxide levels are rising at a rate never seen before by humans.

Lead author, Tammo Reichgelt, a postdoctoral researcher at Columbia University, said: “Some models have shown at the rate we're going right now, the Antarctic Ice Sheet might reach a critical tipping point and start reducing the extent of ice very quickly. We see here that has happened in the past. When the Antarctic ice sheet starts deteriorating, it is not that easy to get it back.”

Researchers examined a 100,000 year period between the Oligocene and Miocene epochs. Before the ice sheet began to melt, atmospheric CO₂ levels rose from 500ppm to between 750 - 1550ppm over 20,000 years. After this it dropped to around 425ppm with positive feedback loops continuing the ice melt. Positive feedback occured as both the result and the effect directly caused the other to increase.

Reichgelt said: “This is the first time we have found evidence that CO₂ fluctuations of this magnitude can happen on relatively short time scales.” These measurements were achieved using carbon isotopes of fossilised leaves as well as the number of stomata present. During times of higher CO₂ concentration, stomata – openings which enable leaves to ‘breathe’ in CO₂ and release O₂ - numbers decrease. This is due to less CO₂ absorption needed by plants.

Researchers are still unsure of what caused the CO₂ spike that led to the ice melt. It could be linked to large amounts of organic material that built up in the Southern Ocean near the Antarctic. The scientists believe this matter then began oxygenating quickly and released large amounts of CO₂.

The study was published in Earth and Planetary Science Letters.