The deep seabed, a hostile and uncharted environment

The depths of the ocean have been the source of endless fantasies and stories, and the absence of light adds a mysterious and spooky dimension to this environment.

Below 200 metres, sunlight no longer penetrates to the depths and we reach what is known as the aphotic zone. The lack of light means that plant life disappears because photosynthesis relies on the sun’s energy. Phytoplankton, at the base of food chains, can no longer develop.

At the surface of the sea, the pressure averages just over 1 bar; once underwater, it increases by 1 bar for every 10 m of depth. This means that water pressure reaches 1,000 bar in the vast ocean trenches at a depth of 10,000 metres.

This immense pressure is equivalent to 1 metric ton pressing down on your little finger or the weight of a small car on a postage stamp.

Here too, the animals have successfully adapted to this environment and to the ambient pressure. For example, the pink snailfish has been seen at a depth of 8,336 metres in the Pacific, in the Izu-Ogasawara Trough, which joins the Mariana Trench. This fish, which breaks all depth records, has a soft skeleton, a gelatinous body with no scales and no swim bladder, and it could not survive at the surface of the ocean. 

The cold conditions that prevail at the bottom of the sea make it an unwelcoming environment. Temperatures average no more than 3°C all year round, and even fall to as low as 0.5°C below 5,000 metres. 

This hostile world does not prevent life from developing.

It is a simple fact that scientists are constantly learning as they explore the deep seabed: in areas where there is little food and no photosynthesis, life in the abyss is extremely abundant and remains largely undiscovered. In some recently explored areas, scientists estimate that 90% of the species living there are new to science!

The deep seabed still has many secrets to reveal and it is vital that these vulnerable ecosystems are protected and preserved.