Scientists have found the possible source of a huge carbon dioxide 'burp' that happened some 18,000 years ago and which helped to end the last ice age.The results provide the first concrete evidence that carbon dioxide (CO2) was more efficiently locked away in the deep ocean during the last ice age, turning the deep sea into a more 'stagnant' carbon repository – something scientists have long suspected but lacked data to support.
Working on a marine sediment core recovered from the Southern Ocean floor between Antarctica and South Africa, the international team radiocarbon dated shells left behind by tiny marine creatures called foraminifera.
By measuring how much carbon-14 (14C) was in the bottom-dwelling forams' shells, and comparing this with the amount of 14C in the atmosphere at the time, they were able to work out how long the CO2 had been locked in the ocean.
According to Dr Skinner: "Our results show that during the last ice age, around 20,000 years ago, carbon dioxide dissolved in the deep water circulating around Antarctica was locked away for much longer than today. If enough of the deep ocean behaved in the same way, this could help to explain how ocean mixing processes lock up more carbon dioxide during glacial periods."
Because the ocean is a large, dynamic reservoir of carbon, it has long been suspected that changes in ocean circulation must have played a major role in motivating these large changes in CO2. In addition, the Southern Ocean around Antarctica is expected to have been an important centre of action, because this is where deep water can be lifted up to the sea surface and 'exhale' its CO2 to the atmosphere.
Scientists think more CO2 was locked up in the deep ocean during ice ages, and that pulses or 'burps' of CO2 from the deep Southern Ocean helped trigger a global thaw every 100,000 years or so. The size of these pulses was roughly equivalent to the change in CO2 experienced since the start of the industrial revolution. link
