The deep ocean.

Updated: Jul 8, 2018

We urgently need to increase our knowledge to better protect the deep ocean.

Last week on the second episode of the series Blue Planet II “The Deep” narrated by Sir David Attenborough took us down to the depths of the ocean. From the Sea Toad that has evolved feet, the Barreleye fish with a transparent head, the cannibal Humboldt squids to the six-gill shark and the super cute Flapjack octopus. It was absolutely fascinating to discover the wonderfully strange animals that can be found in the Earth’s most mysterious habitat.

The average depth of the entire ocean is about 3.5km which means that most of the living space on the planet is in the deep sea. The fact that somehow, the ocean manages to sustain such a diverse range of life in its depths is simply astonishing. Not to mention the volcanic activity on the ocean floor, where three-quarters of volcanic activity on the planet occurs and where life on Earth may have begun four billion years ago.

The deep ocean is part of our very own world and yet we know less about it than the surface of Mars or the Moon. Not a long time ago, the deep seas were described as a vast desert and certain scientists even believed that there was no life there due to the very tough condition but the technological advances over the last century allowed us to explore them and we are just beginning to understand them. Major discoveries have been made since 1977 but there may be yet other life-altering discoveries to be found at the bottom of the sea. We are also starting to evaluate the impact we have on them.

An increase in dissolved CO2 and in temperature has already been evidenced at a depth of more than 1,000 m in some ocean regions which means that disturbance already affects the entire water column. Not to mention, plastic litter, fishing nets and other human litter that can also be found in the deepest ocean depths. Many scientists during deep sea surveys keep discovering the presence of marine litter in areas where they had never been before which means that human litter got to the bottom of the ocean before we even got a chance to go there…

Despite its depth and distance, the deep ocean is vulnerable and increasingly impacted by human activities from pollutants, human waste but also overfishing and seafloor extractive activities (seabed mining, energy extraction, etc.). Moreover, climate change is also a threat with anthropogenic CO2 emissions that have resulted in warming, acidification and deoxygenation. Yet, the deep ocean, covering over half of the planet and encompassing 95% of its habitable volume, deserves particular attention in the context of global warming at so many levels. The deep ocean provides ecosystem services making it crucial in climate mitigation and adaptation.

These different services which are just starting to be discovered are key to the sequestration of heat and carbon as well as in supporting nutrient cycling on which the entire food web (and fisheries for example) relies. The deep ocean is the largest reservoir of carbon on Earth and represents the ultimate sink for most anthropogenic carbon. According to the IPCC 5th Assessment report, the ocean absorbs 90% of the extra heat trapped by greenhouse gas emissions produced by human activities, with 30% of it being stored at depths >700m.

What is for sure is many challenges need to be addressed in the deep sea from the lack of scientific research as well as public engagement to jurisdictional gaps existing in ocean governance. We urgently need to increase our knowledge to better protect the deep ocean. Scientific research is crucial for the health of the ocean, the planet and for us because we cannot protect what we don’t know and what we don’t understand.


An article by Emilie Chartier

Cover Photo: (c)(BBC)

Ocean and Climate Platform “The Ocean revealed”, CNRS Edition, 2017

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