The deep seabed, an ally of the climate

The deep seabed is a hot topic in the news, and one that is receiving more and more media coverage. In fact, in 2024, discussions will resume within the International Seabed Authority (ISA) and decisions are imminent on the mining of its resources against a backdrop of tension over the availability of the minerals needed for the energy transition.

Scientists are warning of the consequences that mineral extraction would have on deep-sea biodiversity and on the ability of these deep-sea environments to regulate the climate. 

Did you know that the ocean absorbs 30% of the carbon emitted by human activities and that the abyss is a “carbon sink”? 

We’re going to take a closer look at the role of the deep ocean in regulating the climate.

The ocean covers 71% of the planet and determines the climatic conditions that prevail on the Earth’s surface. The ocean has absorbed approximately 90% of the heat and 30% of the CO2 emitted into the atmosphere by human activities. 

By absorbing and storing the primary greenhouse gas, the ocean plays a fundamental role in regulating the climate.  

CO2 is transferred from the atmosphere to the oceans by two mechanisms. The first is called the “physical pump”: 90% of absorption takes place when cold water sinks to the high latitudes, carrying dissolved CO2 with it to the seabed. 

The second mechanism, called the “biological pump”, involves living organisms. Phytoplankton algae bind CO2 through the process of photosynthesis. Once dead, the phytoplankton sinks to the bottom where some of the carbon it contains is trapped in mineral form in marine sediments for centuries.

Therefore, the deep seabed is a CO2 “sink”.

This is a matter of fact. When you breathe, half of the oxygen that fills up your lungs comes from the ocean!
And this oxygen is produced by ocean plant plankton, which binds CO2 through the process of photosynthesis.

•    Extracting minerals using machines that dig into the ocean floor could release the carbon and methane trapped in the sediments and disrupt the ocean’s carbon sequestration role.
•    Mining would also have consequences for deep-sea biodiversity, and a study published by Ifremer in Nature Communications shows the contribution of plumes to “carbon assimilation rates in the deep ocean. In fact, the micro-organisms living in hydrothermal plumes “transform around 3% of the total organic carbon dissolved in water into what is known as particulate carbon”.

Photo : Ifremer