Greenhouse gas emission by oceans rising due to global warming

Rising temperatures can indirectly increase the amount of greenhouse gases emitted by the oceans, a study shows.

While previous studies had shown that warming climates lower iron levels at the sea surface, the new study pointed out that a lack of iron at the ocean surface can limit the effect of other key elements in helping plankton (tiny marine organisms) take up carbon.

Plankton absorb CO2 from the atmosphere at the ocean surface and can lock away vast quantities of carbon naturally emitted by oceans.

"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 Laetitia Pichevin from University of Edinburgh in Britain.

If warming climates lower iron levels at the sea surface, as it occurred in the past, this is bad news for the environment, Pichevin said.

For the study, scientists studied a 26,000-year-old sediment core taken from the Gulf of California to find out how the ocean's ability to take up atmospheric CO2 has changed over time.

They tracked the abundance of the key elements silicon and iron in the fossils of plankton in the sediment core.

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.

This is the first study to pinpoint a link between iron and other key marine elements involved in regulating atmospheric CO2 by the oceans.

The study appeared in the journal Nature Geoscience.