Southern oceans release a lot of trapped CO2 into the atmosphereCreative Commons

There was a mysterious warming of the Earth around 11,000 years ago which invariably led to the development of what is now seen as modern human civilisation and activity in oceans are to blame. Oceans are Earth's most important depository for atmospheric carbon dioxide in both long and short-term time scales.

However, oceans' capacity to locking away greenhouse gases can be weakened by activity in the southern oceans, and this might have led to the aforementioned warming event.

According to research carried out by an international team of scientists, the warming of that time period was stabilized because there was a steady rise in carbon dioxide levels around the world, notes a report by Princeton University. This is why understanding why there was a rise in CO2 is of important, said Daniel Sigman, of Princeton.

The actual cause for this spike in CO2 remains unknown to this day, but there are several hypotheses proposed by various scientists attempting to explain it. Now, scientists from Princeton and the Max Planck Institute are pointing at a southern ocean upwelling as the cause for all this excess carbon dioxide.

"We think we may have found the answer," said Sigman. "Increased circulation in the Southern Ocean allowed carbon dioxide to leak into the atmosphere, working to warm the planet."

Apart from explaining how the Earth warmed up 11 millennia ago, it can also be used to model the implications of global warming on ocean circulation and to try to measure how much atmospheric carbon dioxide will rise out of the waters due to fossil fuel burning, notes the report.

For many years now, researchers have known for a fact that the growth and shrinking of phytoplankton in the sea can pump CO2 into the ocean, this process is called the "biological pump". This pump is also mostly driven by low latitude or southern oceans but this cycle pumps CO2 back into the atmosphere closer to the poles, because of the exposure of deep waters to the surface, explained Sigman. The worst offender, that is the ocean that leaks the most CO2 back into the atmosphere is the ocean that surrounds Antarctica.

"We often refer to the Southern Ocean as a leak in the biological pump," Sigman said.

The research team found that increased activity in the Southern Ocean might be responsible for the warming and stabilising climate during the Holocene—time period that stretched over 10,000 years before the Industrial Revolution.

It is this warming during the Holocene that played a critical part in leading humanity to discover and spread out over many parts of the planet that were previously under the cover of ice. The Holocene period is known as the interglacial period because of this, notes the report. It, in turn, led to civilisations being formed in various parts of the world as agricultural growth happened.

The paper was first published in the journal Nature Geoscience.