Life in the ocean's twilight zone is predicted to see drastic decreases and even extinction as seas warm and less food gets to the murky depths, as per a new study.

Between 200 and 1,000 meters below the surface, the twilight zone is the habitat of a wide range of species and creatures, most notably adapted fish-like lantern sharks and kite-fin sharks, which have enormous eyes and bright, bioluminescent skin.

Animals living in the twilight zone eat billions of tons of organic stuff that drifts from the surface of the ocean, including dead phytoplankton and fish waste. Marine snow is the term for the drifting particles.

Warmer seas were, in fact, decreasing the amount of food that sank down to the zone, which means up to 40% of life in the twilight waters may be extinct by the end of the century, as per the study, which was published in Nature. It might take a thousand years to recover.

“The rich variety of twilight zone life evolved in the last few million years, when ocean waters had cooled enough to act rather like a fridge, preserving the food for longer and improving conditions allowing life to thrive,” said Katherine Crichton, the study’s lead author and a postdoctoral research fellow at the University of Exeter.

“According to the studies we have done, 15m years ago there wasn’t all this life [in the twilight zone] and now, because of human activity, we may lose it all. It’s a huge loss of richness,” Crichton said as quoted by The Guardian.

“Unless we rapidly reduce greenhouse gas emissions, this could lead to the disappearance or extinction of much twilight zone life within 150 years, with effects spanning millennia thereafter,” she added.

Paul Pearson, a researcher at Cardiff University, stated that warmer oceans also resulted in less carbon being stored. This is due to the fact that rather than sinking further, the "carbon that is sinking down as part of the marine snow" is essentially eaten up by bacteria closer to the surface. 

Crichton said, “We still know relatively little about the ocean twilight zone, but using evidence from the past we can understand what may happen in the future.”

Three potential scenarios for the twilight zone were presented in the study: a low-carbon scenario, which permits a total of 625 billion tonnes of emissions from 2010 onward; a medium scenario, which permits 2,500 billion tonnes; and a high scenario, which permits 5,000 billion tonnes. According to Crichton, "If we reach the medium or high scenario, both are very bad news for the twilight zone."

The University of Exeter-led worldwide Carbon Budget anticipated that in 2022, total worldwide CO2 emissions would exceed 40.6 billion tonnes, which helps put the emission statistics into perspective. Most of the CO2 in the study's low-carbon scenario has already been released into the atmosphere, with emissions coming close to 40 billion tonnes annually between 2010 and 2012.

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