Even The Deep Sea Is Not Safe From Climate Change

Life in the deep sea beyond the mesopelagic layer of the ocean. Schmidt Ocean Institute

It's easy to think of the deep ocean as a timeless abyss that remains unchanged for thousands of years, quietly humming at a slower pace to the chaotic world above. But new research has shown that climate change is already knocking at the door of the sometimes otherworldly deep sea, and its inhabitants could soon be in grave danger.

Reporting in the journal Nature Climate Change, an international team of scientists looked at how climate change is projected to affect the biodiversity of the deep ocean. While they found that surface water is warming significantly faster, the ocean deep has already been affected by warming and the deep-sea creatures found here are likely to soon experience further dramatic changes.  

“We used a metric known as climate velocity which defines the likely speed and direction a species shifts as the ocean warms," Isaac Brito-Morales, a marine biologist and PhD student at the University of Queensland in Australia, explained in a statement.

"We calculated the climate velocity throughout the ocean for the past 50 years and then for the rest of this century using data from 11 climate models.”

Their findings suggest that the global mean climate velocities in the darkest and deepest layers of the ocean, over 1,000 meters (3,280 feet), have been accelerated nearly four times faster than at the surface over the latter half of the 20th century.

Life in the deep sea (<200m). Schmidt Ocean Institute

Things are only set to worsen over the coming decades, too. In the mesopelagic layer of the ocean, the “twilight zone” between 200 to 1,000 meters (656 to 3,280 feet) where sunlight begins to fade to black, climate velocities are projected to be accelerated 4 to 11 times higher than currently at the surface by the end of this century. If accurate, this is will have a huge knock-on effect throughout the wider oceans since the mesopelagic layer is home to a rich array of small fish that support larger animals, including tuna and squid.

The changes in climate velocities are more severe in the deep ocean as the temperature is generally fairly uniform and constant compared to the surface waters, which bears the brunt of most atmospheric changes that occur above the surface. Even slight change in the dark depths, however, can really rock the boat and profoundly disturb the wider ecosystem. 

Of course, all of this is subject to change depending on how climate change pans out and whether greenhouse gas emissions are successfully slashed in the coming years. On top of warming temperatures, there are a handful of other things to consider when we look at the effect of climate change on the deep ocean’s wildlife. The researchers also point out that the biodiversity of the deep sea is also influenced by other conditions such as pressure, light levels, oxygen concentrations, etc. 

However, even under some of the most optimistic climate change predictions, the biodiversity of the deep sea is likely to feel burn in the coming century. 

"The acceleration of climate velocity for the deep ocean is consistent through all tested greenhouse gas concentration scenarios. This provides strong motivation to consider the future impacts of ocean warming to deep ocean biodiversity, which remains worryingly understudied," added Jorge Garcia Molinos, a climate ecologist at Hokkaido University's Arctic Research Center in Japan, who contributed to the study.

Climate velocity between 1955-2005 (far left) and projected future sea temperatures (2050-2100) at sea surface and the mesopelagic layer under three greenhouse gas emission scenarios. Isaac Brito-Morales et al., Nature Climate Change. May 25, 2020

 

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