Carbon dioxide released from the oceans brought about the end of the last Ice Age (Glacial Period), British and Australian scientists have revealed in a new study. CO2 that was stored deep in the ocean helped warm up the planet.
The researchers, from the Australian National University (ANU) and the University of Southampton in England said their findings will give scientists a deeper insight into how the oceans affect climate change and the carbon cycle.
Their study has been published in the academic journal Nature.
During the last Ice Age, much of North America and Northern Europe were permanently iced over.
Dr. Gianluca Marino, works at the Research School of Earth Sciences, part of ANU, said:
“The ocean currently contains about 60 times more carbon than the atmosphere – in natural conditions it is the main driver of carbon dioxide variations. Carbon can exchange rapidly between the ocean and the atmosphere.”
Carbon dioxide levels in the Earth’s atmosphere have ranged from about 185 ppm (parts per million), as occurred during the last Ice Age, to 280 ppm during the other periods over the past thousand years.
Since 1980, carbon dioxide levels have reached nearly 400 ppm.
Ice melted over 9,000 years in last Ice Age
North America and Scandinavia were once covered with over 50 million cubic kilometers of ice. It gradually melted away from about 19,000 to 10,000 years ago. Enough water was released from this melting to raise the sea level by approximately 130 meters.
In this latest study, the researchers examined levels of boron, an element found in the shells of micro-fossils recovered from the ocean floor, to reconstruct ancient carbon dioxide levels. They compared them with the Co2 levels previously registered in the Antarctic ice cores.
The team found that at the end of the last ice age, reconstruction of carbon dioxide dissolved in the ocean from tiny organisms that existed at the surface of the South Atlantic Ocean and Eastern Equatorial Pacific became significantly higher than atmospheric levels at the time.
Joint-lead author, Dr Miguel Martínez-Botí, said:
“This suggests the ocean was releasing carbon dioxide into the atmosphere, that had been stored deep in the ocean for the period of the ice age.”
When the temperatures are low, as they were during the last Ice Age, there was weaker mixing between the surface and deep ocean, which helped keep carbon trapped in the ocean floor for millennia.
Other oceans may also have played a part
The researchers concluded that at the end of the last Ice Age, carbon that had been trapped deep in the Southern Ocean surfaced and was released into the atmosphere.
Co-author, Dr. Gabin Foster, believes other parts of ocean, such as the Pacific, may have played a similar road.
Dr. Foster said:
“Our results support a primary role for the Southern Ocean, but we don’t yet know the full story. The new data confirms that natural variations in atmospheric carbon dioxide are linked to carbon stored in the oceans.”
“We have observed this recently – the oceans have stored more than 30 per cent of humanity’s fossil fuel emissions over the last 100 years or so.”
Reference: M. A. Martínez-Botí, G. Marino, G. L. Foster, P. Ziveri, M. J. Henehan, J. W. B. Rae, P. G. Mortyn & D. Vance. “Boron isotope evidence for oceanic carbon dioxide leakage during the last deglaciation.” Nature 518, 219–222, (12 February 2015), doi:10.1038/nature14155.