Marine algae reveal close link between past climate and CO2
The ocean is filled with microscopic algae that take up carbon dioxide (CO2) from the atmosphere in order to grow. A new study by researchers from the Geology Department at the University of Oviedo (Spain) shows that the algae may adapt to rising levels of atmospheric CO2 much sooner than previously thought, and in an unexpected way. This study, published in Nature and co-authored by ERC grantee Heather Stoll, also provides evidence for a much closer link between atmospheric CO2 decrease and cooling and glaciations in the geological past.
The amount of carbon dioxide in the atmosphere is central to climate, because it regulates the greenhouse effect. It is also central to all the earth’s plants – on land and in the sea – because it is the key ingredient used for photosynthesis. When CO2 levels are low, photosynthesis may not proceed as rapidly, so plants have developed coping mechanisms. Many marine algae use and transport supplementary “fuels”, other more abundant forms of carbon in the ocean like bicarbonate (the form of carbon in baking soda) for photosynthesis. But this approach takes extra energy and nutrients. So algae might be expected to stop this extra accumulation when CO2 increases.
The unveiled secrets of marine algae
The new study, co-authored by ERC grantee Heather Stoll and Clara Bolton, uses a new indicator to track when algae forego one of the key “coping mechanisms”. The result sheds light on both the adaptation of algae to CO2 as well as the history of CO2 in the atmosphere. Because some algae make microscopic shells that accumulate on the sea floor, just like clams make shells that accumulate on the shore, it is possible to use these fossil shells to understand how ancient algae coped with CO2 levels when they were alive. A new model of how algal cells transport carbon shows there is a change in the chemical makeup of the shells when the cell needs to use supplementary “fuels” like bicarbonate to grow. By measuring the chemistry of fossil shells in the ocean over the past 60 million years, the research team showed that algae started to rely heavily on these supplementary carbon sources relatively recently, between 7 and 5 million years ago.