All those CO2-absorbing hopes pinned on tiny algae have experienced yet another setback, as European researchers find that warmer ocean temperatures cause bacteria to devour increasing masses of algae, meaning less can sink to the sea bottom with its stored carbon.

Scientists are already dealing with the disappointment from last month’s ocean-fertilisation experiment, in which German and Indian researchers discovered that seeding the seas with dissolved iron not only spurs algae growth — a good thing — but attracts mobs of hungry zooplankton that eat the algae — a bad thing.

And now marine scientists from the Leibniz Institute of Marine Sciences, the Alfred Wegener Institute for Polar and Marine Research and the Leibniz Institute for Baltic Sea Research have found another bad thing: algae-eating bacteria.

The researchers found that, while the metabolic rate of planktonic algae does increase with rising water temperatures, their level of carbon uptake doesn’t increase proportionally. That’s because warmer temperatures also fuel more bacterial growth, which causes algae to degrade before it can sink to the sea bottom with its absorbed carbon dioxide.

“This study underscores the importance to improve the incorporation of biological processes and feedbacks in Earth system models,” said Julia Wohlers, the study’s lead author.

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