Science

Terrawatch: the adventurous icebergs that trigger ice ages


How does an ice age start? We know that changes in the Earth’s orbit around the sun alter the amount of solar energy reaching our planet, but it has long been a mystery as to how this triggers such a dramatic change in the climate. A study shows that Antarctic icebergs may be responsible for tipping the balance.

Aidan Starr, from Cardiff University, and his team analysed sediments recovered by the International Ocean Discovery Program from the ocean floor south of South Africa. Within those sediments were tiny fragments of rock dropped by melting Antarctic icebergs. By studying the chemistry of the tiny deep-sea fossils found throughout the sediment core, the scientists were able to show that when climate conditions enabled icebergs to travel this far north they made the North Atlantic fresher and the Southern Ocean saltier.

Climate and ocean simulations revealed that this pulse of freshwater to the North Atlantic triggered changes in ocean circulation patterns that led to more carbon dioxide being pulled out of the Earth’s atmosphere, helping to plunge the planet into an ice age. The results, which were published in Nature, show that every glacial period over the last 1.6m years is associated with Antarctic icebergs straying farther north than normal.



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