In a commentary in the journal Nature, published ahead of a UN oceans summit in France, researchers and conservationists called on governments to act more decisively to protect marine habitats outside national jurisdiction.

They warned that exploitation of the high seas, including new proposals to mine the seabed and fish for species at greater depths, "risks doing irreversible damage" to life in the ocean, as well as undermining its crucial role in regulating the world's climate.

A landmark treaty to protect the high seas -- adopted in 2023 but still only halfway to ratification -- will be in the spotlight at the June 9 to 13 UN Ocean Conference in Nice.

It is seen as crucial to meeting the globally-agreed target of protecting 30 percent of oceans by 2030.

But the experts behind the Nature commentary, entitled "Why we should protect the high seas from all extraction, forever", say countries should go further.

Lead author Callum Roberts, Professor of Marine Conservation at Britain's University of Exeter, said the world should take as an example the global agreement to protect Antarctica as a "planetary commons that is really important for all life on Earth".

"(They should agree to) keep it intact and undisturbed, so we don't release these potentially catastrophic consequences from exploitation that we can't control," he told AFP.

The high seas cover nearly half of Earth's surface but less than one percent is currently protected, the authors said.

Exploitation of the open ocean goes back to the intensification of whaling in the 17th century, causing dramatic depletion of the global whale population.

Since then humans have turned to harvesting sharks, fish and squid.

But the Nature article authors stress that marine animals do not just provide food and other products for humans -- they also form part of the Earth's carbon cycle which is essential to the very air we breathe.

Some animals living in the "twilight zone", at depths between 200 and 1,000 metres (650 and 3,300 feet) swim up towards the surface to feed at night and dive back down, depositing carbon-rich faeces deep in the ocean.

This happens at such a huge scale that it affects the balance of carbon dioxide in the atmosphere.

Roberts said that research suggests that without this process the world would already be up to three degrees hotter than the pre-industrial era. Global surface temperatures last year averaged just over 1.5C.

- 'Self interest' -

Another process sees nutrients redistributed as dead plants, animals and excretions sink down from the surface, providing sustenance for more life which in turn takes up more CO2.

This natural cycle has already been slowed by centuries of intensive exploitation and is now further threatened by pressure to fish at greater depths, mainly to provide fishmeal and oil for aquaculture, the authors said.

This risks both reducing a key food source for tuna, sharks and dolphins, but also curbing the amount of carbon the ocean can take up.

High-seas fishing is prone to by-catch that kills millions of sharks every year and thousands of turtles and seabirds. A total ban, the authors say, would enable species recovery that would significantly improve potential catches closer to shore.

Protecting these animals is not an "act of self sacrifice, but of self interest" said Roberts.

"The planet is in a very dangerous place in terms of the rapidity of climate change, and we need to pull all the levers that we can right now to slow the pace."

Another concern is deep-sea mining.

Would-be miners eager to extract mineral-rich nodules from the deepest ocean floor have so far been held back by efforts to regulate such potentially damaging exploration.

But US President Donald Trump recently sparked global outrage with an order to fast-track deep-sea mining in the open ocean outside American territorial waters.

Roberts said "the argument that we've got to go there to power the green transition is total nonsense".

He said that while governments may balk at a sweeping moratorium on exploitation of the high seas, they should understand that "things are much harder to stop when they've already begun".