Warming Climate Accelerates Emission of Ocean Carbon Dioxide

Climate change and oceans are inextricably tied; a new study found that increasing temperatures might further speed up emissions of carbon dioxide from oceans.

Researchers at the University of Edinburgh provide fresh insights into how oceans affect the level of atmospheric carbon dioxide (CO2). In this study they reveal that increasing temperatures indirectly raise the amount of the greenhouse gas emitted by oceans.

The finding is based on the analysis of a 26,000 year-old sediment core from the Gulf of California. Using this ancient sediment core the researchers studied oceans' ability to suck in atmospheric CO2 and how it has changed over the years. In the same sediment core, they traced the key elements silicon and iron that were present in large volumes in the fossilized planktons-the tiny marine organism.

Planktons, the microscopic organism, play a key role in the oceanic carbon cycle.   They absorb carbon from the atmosphere and store it for long.

Researchers found that, "those periods when silicon was least abundant in ocean waters corresponded with relatively warm climates, low levels of atmospheric iron, and reduced CO2 uptake by the oceans' plankton."

It was long suspected that iron plays a crucial role in aiding planktons suck up CO2. But this new study found that when the levels of iron drop at the ocean surface, it reduces the effect of other key elements in supporting planktons' absorption of carbon. This effect is more in the southern oceans and equatorial Pacific and coastal areas. They play a key role in influencing levels of CO2 in the global atmosphere.

"If warming climates lower iron levels at sea surface, as occurred in the past, this is a bad news for the environment," says Dr Laetitia Pichevin, from the School of GeoSciences.

Through this finding, the researchers highlight the complex association between iron and other key marine elements present in the oceans that help control atmospheric CO2.

"Iron is known to be a key nutrient for plankton, but we were surprised by the many ways in which iron affects the CO2 given off by the oceans," said Pichevin.

The finding was documented in Nature Geoscience.