Atlantic Ocean bigger carbon sink ...

... than previously expected.

Moreover, much of this carbon ends up in long-term storage instead of being recycled quickly like most carbon in the ocean. That's because the main photosynthesisers are diatoms, single-celled algae that build a heavy silica shell around their bodies.

This glassy shell makes diatoms sink rapidly after they die, removing 20 million tonnes of carbon from the atmosphere each year, the researchers estimate.

That's not much compared to the amount emitted by human activity each year but it represents a major shift in our knowledge of the oceans' carbon balance, says Subramanian. And although the Amazon is the largest of the world's rivers, other major tropical rivers such as the Congo and the Orinoco may have similar effects, he says – a conjecture he is now aiming to test.

Now, time to use this to our advantage.