Did carbon dioxide released from the ancient ocean help bring the Earth out of its last ice age? New research on deep oceanic carbon stores suggests so.
The recent findings could provide insight into how the ocean influences both the carbon cycle and climate change, the Australian National University reported.
"The ocean currently contains about 60 times more carbon than the atmosphere - in natural conditions it is the main driver of carbon dioxide variations," said joint lead researcher, Gianluca Marino, from The Australian National University (ANU) Research School of Earth Sciences. "Carbon can exchange rapidly between the ocean and the atmosphere."
Atmospheric carbon dioxide levels fluctuate between about 185 parts per million (ppm) during the most recent ice age to around 280 ppm during warmer periods, such as modern times. Since 1850, carbon dioxide levels have risen by as much as 400 ppm.
To make their findings, the researchers reconstructed ancient carbon dioxide levels by looking at levels of the element boron in shells of microfossils found on the ocean floor. They compared these observations with atmospheric carbon concentrations measured from Antarctic ice cores. The researchers found that at the age of the last ice age, reconstructions of carbon dioxide dissolved in the ocean from tiny organisms that live on the surface rose in the South Atlantic Ocean and eastern equatorial Pacific.
"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," said joint lead author, Miguel Martínez-Botí from the University of Southampton.
The mixing between shallow and deep ocean water is believed to have been weaker during the most recent ice age, keeping carbon trapped at the bottom of the ocean for millions of years. At the end of the last ice age, these carbon stores are believed to have been re-released into the atmosphere.
"The new data confirms that natural variations in atmospheric carbon dioxide are linked to carbon stored in the oceans," said co-author Gavin Foster, from the University of Southampton. "We have observed this recently - the oceans have stored more than 30 [percent] of humanity's fossil fuel emissions over the last 100 years or so."
The findings were published in a recent edition of the journal Nature.
