An ice age store

By | Science & Technology
The Perito Moreno glacier, Argentina.Credit@flickruser-ChrisFord

A vast carbon dioxide reservoir existing for thousands of years has been discovered in the South Pacific. Using sediment cores, scientists have documented the carbon dioxide levels and carbon exchange cycles during interglacial and glacial periods.

The global carbon cycle influences the level of carbon dioxide (C02) in the atmosphere and potentially stores it in oceans for thousands of years. The share of carbon dioxide in the atmosphere differs between glacial and interglacial periods. The transition between an interglacial period and an ice age is always accompanied by a reduction in atmospheric C02. During an ice age the deep ocean may store this CO2 in reservoirs. In post-glacial periods ocean currents influence the release of carbon dioxide back into the atmosphere.

The power of the ocean to drive the atmospheric C02 levels may be explained by the fact the ocean has 60 times more carbon than the atmosphere. An underlying mechanism links the rise of atmospheric C02 to the release of a radio carbon-depleted carbon dioxide. This release is believed to explain historic atmospheric C02 variability. The more evolved a water mass the more enriched in depleted carbon c02 it becomes. This is measured by radio carbon dating, identifying dated glacial water in the North and South Pacific and the South Atlantic.

Ice age temperature changes over thousands of years.Credit@wikipedia

Ice age temperature changes over thousands of years.Credit@wikipedia

The glacial and interglacial periods involve changes to the climate including the development and position of sea ice, westerly winds, changes in water mass (due to changes in C02 levels) and the efficiency of the upwelling circulation. Furthermore, deep water salinity and freshening of intermediate waters may have increased the stratification and restricted the communication between deep waters and the atmosphere. All may be important factors in the evolution of the carbon exchange cycle.

During a glacial period, the drop in sea level due to the increase in mass of the ice sheet increases volcanic activity along mid-ocean ridges on the oceanic plate. This activity may influence the release of c-depleted C02 into the water column in a time delayed fashion, in response to the sea level change.

Recently, a new study published in the journal Nature communications, may have located a reservoir 2000 to 4300 metres in the South Pacific and illuminated its gas emission history. Taking sediment samples from water at the depths of 830 to 4300 metres, a 35,000 year dated record was contained in calcareous shells. These shells were radiocarbon dated and contained important information on the water mass where the organisms lived and importantly the level of carbon dioxide. Dr Thomas Ronge commented, “The more dated the water mass, the more carbon dioxide it stores, because bound carbon in the form of animal and plant remains constantly trickles down from the surface.”

Biological and physical pumps of carbon dioxide.Credit@wikimedia

Biological and physical pumps of carbon dioxide.Credit@wikimedia

“Our results were surprising and indicated the deep South Pacific during this glacial period was augmented with old carbon dioxide from the decomposition of organic material, however also as a result of eruptions of submarine volcanoes,” said Ronge. A clarification of the ice age ocean 20,000 years ago may now be accomplished. “Scientists know from other studies it is likely during the transition from interglacial to ice age a large sea ice cover formed on the Antarctic Ocean, which closed the oceanic ventilation window. At the same time, the Southern Westerly winds moved northwards, so the buoyancy in the Southern Ocean was reduced and only a small amount of deep water reached the surface.” The Southern Pacific is now known to be one of the largest ventilation windows of any of the world’s oceans.

When ocean circulation slowed down the saline water below 2000 metres it evaded contact with the surface for nearly 3000 years. “During this time so much bound carbon in the form of animal and algae remains trickled down from the more intermixed sea surface into the deep water layer, the team were able to identify it as the major carbon reservoir looked for so intensively.”

When the last ice age ended and ice retreated, westerly winds returned to the south, ocean circulation improved and water enriched with carbon dioxide returned to the surface.

How may co2 levels fluctuate?


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