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.
Plankton absorb CO2 from the atmosphere at the ocean surface, and can lock away vast quantities of carbon.
Researchers found 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. Scientists had suspected iron might have a role in enabling plankton to absorb CO2.
It shows a lack of iron at the ocean surface can limit the effect of other key elements in helping plankton take up carbon.