Deep sea stores less and less CO2

The deep sea is considered a gigantic reservoir for carbon dioxide – but its storage capacity is threatened by rising temperatures.


This is the conclusion of a research expedition from the University of Vienna in the North Atlantic. According to the study, the deep sea there has warmed by around 0.1 degrees Celsius over the past two decades. The Viennese research team led by marine biologist Gerhard Herndl was recently on a four-week expedition in the North Atlantic, from Iceland to the Azores. The team was able to collect more than a dozen water samples from the seafloor. The 13 scientists believe these samples contain information about how the deep sea is changing with global warming. Austrian radio station ORF reported this with reference to the researchers. While a tenth of a degree doesn't sound like much, the consequences for the deep sea and the Earth's climate should not be underestimated, Herndl warned on ORF. The deep sea acts as a carbon reservoir, mitigating the progress of global warming. A property that, according to the marine biologist, is under threat.


Carbon reaches the seafloor in the form of small biomass particles. The particles settle on the seafloor, and due to the low temperatures, the carbon is hardly broken down into carbon dioxide by microorganisms there. But the research team observed that this changes as the deep sea warms. This is because the microorganisms on the seafloor become more active as the water warms. "Like all living organisms, bacteria have a higher metabolism at higher temperatures and thus produce more carbon dioxide," Herndl explains to ORF. The microorganisms become hungrier, so to speak, and metabolize more of the carbon that sinks to the bottom. This reduces the storage capacity of the deep sea because a larger portion of the sinking biomass is immediately metabolized back into carbon dioxide and thus returns to the atmosphere, explains Herndl. The ocean's carbon storage capacity is therefore decreasing. Herndl speaks of a "vicious circle": "Every warming of the ocean further increases the respiratory activity of all organisms." If the oceans continue to warm, "the ocean will lose a significant portion of its function as a carbon reservoir."


This also puts an end to ideas of artificially storing carbon in the deep sea. Such considerations are based on the assumption that the carbon supplied as biomass is not degraded due to the low metabolic activity on the seafloor. However, as the oceans continue to warm, biomass is suddenly being degraded in the deep water. According to the marine biologist's calculations, artificial deep-sea carbon storage would therefore be ineffective. Instead, Herndl appealed to ORF for stricter climate and marine protection measures.