Massive ice 'lid' melting led to CO2 release at end of ice age

The melting of a vast 'lid' of sea ice caused the release of huge amounts of carbon dioxide (CO2) into the atmosphere at the end of the last ice age, a new Cambridge study has found.
The study reconstructing conditions at the end of the last ice age suggests that as the Antarctic sea ice melted, massive amounts of CO2 that had been trapped in the ocean were released into the atmosphere.
The study by researchers from the University of Cambridge in the UK includes the first detailed reconstruction of the Southern Ocean density of the period and identified how it changed as the Earth warmed.

The ocean is made up of different layers of varying densities and chemical compositions. During the last ice age, it was thought that the deepest part of the ocean was made up of very salty, dense water, which was capable of trapping a lot of CO2.
Scientists believed that a decrease in the density of this deep water resulted in the release of CO2 from the deep ocean to the atmosphere.
In order to determine how the oceans have changed over time and to identify what might have caused the massive release of CO2, the researchers studied the chemical composition of microscopic shelled animals that have been buried deep in ocean sediment since the end of the ice age.

Like layers of snow, the shells of these tiny animals, known as foraminifera, contain clues about what the ocean was like while they were alive, allowing the researchers to reconstruct how the ocean changed as the ice age was ending.

They found that during the cold glacial periods, the deepest water was significantly denser than it is today.
However, what was unexpected was the timing of the reduction in the deep ocean density, which happened some 5,000 years after the initial increase in CO2, meaning that the density decrease could not be responsible for releasing CO2 to the atmosphere.
The new findings suggest that although a decrease in the density of the deep ocean did occur, it happened much later than the rise in atmospheric CO2, suggesting that other mechanisms must be responsible for the release of CO2 from the oceans at the end of the last ice age.

The findings were published in the journal PNAS.