A Great Carbon Dioxide Burp

There are many earth cycles. One is a cycling between warmer and colder periods which are commonly called ice ages. The causes of these cycles are complex and are related to how much sun radiation we get as well as some slight variation in the sun itself. Scientists have recently found a 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 causes of ice ages are not fully understood for both the large scale ice age periods and the smaller ebb and flow of glacial and interglacial periods within an ice age. The consensus is that several factors are important: atmospheric composition (the concentrations of carbon dioxide for example); changes in the Earth’s orbit around the Sun known as Milankovitch cycles; the motion of tectonic plates (i.e, the present north pole was once hundreds of mile from where it is now), location of the crust in places which affect wind and ocean currents; variations in actual solar output; the impact of some large meteorites, and volcanism including eruptions of super volcanoes.

An “ice age” or, more precisely, “glacial age” is a geological period of long term reduction in the temperature of the Earth’s surface and atmosphere, resulting in an expansion of glacial ice sheets.

Within a long term ice age, individual pulses of extra cold climate are termed “glacial periods”, and intermittent warm periods are called “interglacials”. An ice age implies the presence of extensive ice sheets in the northern and southern hemispheres. By this definition we are still in the ice age that began at the start of the Pleistocene (because the Greenland and Antarctic ice sheets still exist).

So one of the potential causes of a change in an ice age is the atmospheric gas composition. A large release of carbon dioxide can change the overall climate (in this case warm it up)and be a trigger for an interglacial period.

The new carbon dioxide burp results provide the first concrete evidence that carbon dioxide (CO2) was locked away in the deep ocean during the last ice age, turning the deep sea into a more stagnant carbon repository, This is something scientists have long suspected but lacked the data to support.

Working on a marine sediment core recovered from the Southern Ocean floor between Antarctica and South Africa, the international team led by Dr Luke Skinner of the University of Cambridge radiocarbon dated shells left behind by tiny marine creatures called foraminifera.

By measuring how much carbon 14 (14C) was in the bottom dwelling shell creatures, 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.

The team were also able compare their results directly with the ice core record of past atmospheric CO2 variability.

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 may have been an important center of action, because this is where deep water can be lifted up to the sea surface and exhale its CO2 to the atmosphere.

Some scientists think more CO2 was locked up in the deep ocean during the ice ages, and that pulses or burps of CO2 from the deep Southern Ocean helped to trigger global thaws 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.

If this theory is correct, we would expect to see large transfers of carbon from the ocean to the atmosphere at the end of each ice age or glacial period.

If correct, this theory provides evidence of a large release of carbon dioxide that suddenly and dramatically increased atmospheric carbon dioxide levels. This would then cause a sudden temperature increase that would make the ice sheets melt leading to rising oceans and a sudden change in world wide ecologies. Though the industrial revolution liberated a lot of carbon dioxide, the ocean should then act as a giant storage area for the increased carbon dioxide given time.

Article by Andy Soos appearing courtesy ENN

photo: John E. Lester

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