London: Oceans may be responsible for making the Earth move in and out of ice ages every 100,000 years, finds a study.
According to the study published in the journal Geology, oceans sucking carbon dioxide (CO2) out of the atmosphere may have triggered this phenomena.
Dubbed the "100,000-year problem", this phenomena has been occurring for the past million years or so and leads to vast ice sheets covering North America, Europe and Asia.
By studying the chemical make-up of tiny fossils on the ocean floor, the team discovered that there was more CO2 stored in the deep ocean during the ice age periods at regular intervals every 100,000 years.
This suggested that extra carbon dioxide was being pulled from the atmosphere and into the oceans at this time, subsequently lowering the temperature on the Earth and enabling vast ice sheets to engulf the Northern Hemisphere.
"We can think of the oceans as inhaling and exhaling carbon dioxide, so when the ice sheets are larger, the oceans have inhaled carbon dioxide from the atmosphere, making the planet colder. When the ice sheets are small, the oceans have exhaled carbon dioxide, so there is more in the atmosphere which makes the planet warmer," said Carrie Lear, researcher at the Cardiff University, Britain.
"By looking at the fossils of tiny creatures on the ocean floor, we showed that when ice sheets were advancing and retreating every 100,000 years, the oceans were inhaling more carbon dioxide in the cold periods, suggesting that there was less left in the atmosphere," Lear added.
Marine algae play a key role in removing CO2 from the atmosphere as it is an essential ingredient of photosynthesis.
CO2 is put back into the atmosphere when deep ocean water rises to the surface through a process called upwelling. But when a vast quantity of sea ice is present, this prevents the CO2 from being exhaled, which could make the ice sheets bigger and prolong the ice age.
The last ice age ended about 11,500 years ago, and began 21,000 years ago, according to earlier study reports.