Tim Radford / Climate News Network & EcoWatch

Scientists have taken the temperature of the deep seas and found alarming signs of change: ocean warming is prompting many creatures to migrate fast.

 (June 15, 2020) — The species that live in the deep and the dark are moving towards the poles at twice to almost four times the speed of surface creatures.

The implication is that — even though conditions in the abyssal plain are far more stable than surface currents — the creatures of the abyss are feeling the heat.

The oceans of the world cover almost three-fourths of the globe and, from surface to seafloor, provide at least 90% of the planet’s living space.

And although there has been repeated attention to the health of the waters that define the Blue Planet, it remains immensely difficult to arrive at a consistent, global figure for rates of change in temperature of the planet’s largest habitat.

Oceanographers are fond of complaining that humankind knows more about the surface of Mars and Venus than it does about the bedrock and marine sediments at depth.

This may still be true, but repeated studies have confirmed that the ocean floor ecosystem is surprisingly rich, varied and potentially at risk.

Now researchers from Australia, Europe, Japan, South Africa and the Philippines report in the journal Nature Climate Change that although they could not deliver thermometer readings, they had found an indirect measure: the rate at which marine creatures move on because they don’t care for their local temperature shifts.

They call this “climate velocity.” They had data for 20,000 marine species. And they found that overall, at depths greater than 1000 meters, marine creatures have been on the move much faster than their fellow citizens near the surface, over the second half of the 20th century.

Computer simulations tell an even more alarming story: by the end of this century, creatures in the mesopelagic layer — from 200 meters down to 1000 meters — will be moving away between four and 11 times faster than those at the surface do now.

Faster Migrants 

The finding is indirectly supported by a second and unrelated study on the same day in the journal Nature Ecology & Evolution. French scientists looked at studies of more than 12,000 kinds of the migrations of bacteria, plant, fungus and animal to find that sea creatures are already floating, swimming or crawling towards the poles six times faster than those on land, as a response to global heating driven by profligate human use of fossil fuels.

So shifts in range can be interpreted as an indicator of the stress on the ocean habitats. This creates complications for conservationists arguing for internationally protected zones — protected from fishing trawl nets, and from submarine mining operations — because, if for no other reason, not only are ocean creatures moving at different speeds at different depths; some of the shifts are in different directions.

“Significantly reducing carbon emissions is vital to control warming and help take control of climate velocities in the surface layers of the ocean by 2100,” said Anthony Richardson of the University of Queensland in Australia, one of the authors.

“But because of the immense size and depth of the ocean, warming already observed at the ocean surface will mix into deeper waters. This means that marine life in the deep ocean will face escalating threats from ocean warming until the end of the century, no matter what we do now.

“This leaves only one option — act urgently to alleviate other human-generated threats to deep sea life, including seabed mining and deep-sea bottom-fishing.”

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