Stagnant, warm deep sea helped end last Ice Age

The build-up and subsequent release of heat from stagnant water of Arctic Ocean and Nordic Seas played a role in ending the last ice age within the Arctic region, says new research.

"As well as being stagnant, these deep waters were also warm," said lead researcher David Thornalley from University College London.

The study examined how the circulation of the ocean north of Iceland - the combined Arctic Ocean and Nordic Seas, called the Arctic Mediterranean - changed since the end of the last Ice Age ( approximately 20,000-30,000 years ago).

Today, the ocean is cooled by the atmosphere during winter, producing large volumes of dense water that sink and flush through the deep Arctic Mediterranean.

However, in contrast to the vigorous circulation of today, the research found that during the last Ice Age, the deep Arctic Mediterranean became like a giant stagnant pond, with deep waters not being replenished for up to 10,000 years.

This is thought to have been caused by the thick and extensive layer of sea ice and fresh water that covered much of the Arctic Mediterranean during the Ice Age, preventing the atmosphere from cooling and densifying the underlying ocean.

Sitting around at the bottom of the ocean, they slowly accumulated geothermal heat from the seafloor, until a critical point was reached when the ocean became unstable.

"Suddenly, the heat previously stored in the deep Arctic Mediterranean was released to the upper ocean. The timing of this event coincides with the occurrence of evidence for a massive release of meltwater into the Nordic Seas," Thornalley noted.

"We hypothesise that this input of melt water was caused by the release of deep ocean heat, which melted icebergs, sea-ice and surrounding marine-terminating ice sheets," Thornalley said.

The study was published in the journal Science.