Life in the ocean’s ‘Twilight Zone’ could disappear due to the climate crisis | CNN

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One of the largest habitats on Earth could be reducing its rich biodiversity by the end of the century due to the climate crisis.

The mesopelagic zone of the ocean, also called the “twilight zone,” is between 656 feet and 3,280 feet (200 meters to 1,000 meters) below the surface.

The marine region, which makes up about a quarter of the ocean’s volume, is home to billions of tons of organic matter and some of the most impressive biodiversity on Earth, despite being beyond the reach of sunlight.

The twilight zone is also a crucial habitat for marine life that dives in search of prey, such as sharks or lanternfish, which hide in the twilight zone during the day and swim to the surface waters to feed at night.

New research warns that the climate crisis could reduce life in the twilight zone by 20 to 40 percent by the end of the century. And if greenhouse gas emissions continue, researchers estimate that life in the marine region could be severely depleted within 150 years – and may not recover for thousands of years.

Paleontologists and ocean scientists have teamed up to study the effects on the ocean’s twilight zone during previous ancient warming events to predict how the habitat will respond to global warming in the future. The research team examined drill cores from the sea floor, which contained evidence of conserved microscopic shells of plankton.

Over time, the calcareous shells accumulate on the sea floor and preserve information about what the environment was like during their life. The tiny shells effectively form a timeline of how the ocean has changed over millions of years.

A study detailed the results published Thursday in the journal Nature Communications.

“We still know relatively little about the ocean’s twilight zone, but using evidence from the past we can understand what might happen in the future,” said the study’s lead author, Dr. Katherine Crichton, a postdoctoral fellow at the University of Exeter in the United Kingdom, in a statement.

The researchers focused on two interglacial periods, 15 million years ago and 50 million years ago, when even ocean temperatures were “significantly warmer than today,” according to the study.

“We found that the Twilight Zone was not always a rich habitat teeming with life,” study co-author Paul Pearson, an honorary professor at Cardiff University in the United Kingdom, said in a statement. “During these warm periods, there were far fewer organisms living in the twilight zone because far less food was arriving from surface waters.”

Particles of organic matter from the sea surface drift downward and serve as one of the main food sources for twilight zone life. But past warming events caused the material to be broken down more quickly by bacteria, so less of it ended up in the ocean region.

According to the study, warmer ocean temperatures also increase organisms’ metabolic rates, resulting in increased food requirements and oxygen consumption.

“The rich diversity of life in the twilight zone evolved over the past few million years, when seawater cooled enough to function more like a refrigerator, preserving food longer and improving the conditions for life to thrive.” said Crichton.

Luiz A. Rocha, Curator and Follett Chair in Ichthyology at the California Academy of Sciences, worries changes are afoot that have not been recognized because the Twilight Zone is so underexplored, largely due to a discrepancy between funding and the Cost of their exploration is attributable to region.

Rocha, who was not involved in the study, is exploring the twilight zone and the mesophotic zone just above, which is between 30 and 150 meters below the surface.

“There’s no baseline to compare what we’re measuring against, so this study looking at the composition of the fossil record over time is one of the few ways we can try to understand how we see the twilight zone changing.” cause.” said Roche.

Based on what they discovered about the ancient warming events, the researchers combined this data with the Earth System Mode Simulations – Modeling of the Earth’s carbon cycle as it moves through land, sea and atmosphere.

The team’s work revealed what’s currently going on in the Twilight Zone and how that could change in the future over decades, centuries and even millennia as the world warms.

“Our results suggest that significant changes may already be underway,” Crichton said. “If we don’t reduce greenhouse gas emissions quickly, it could lead to the disappearance or extinction of many creatures in the twilight zone within 150 years, with impacts stretching thousands of years thereafter. Even a low-emission future can have significant impacts, but that would be far less severe than medium- and high-emission scenarios. Our study is a first step in understanding how vulnerable this oceanic habitat might be to global warming.”

Researchers used three emission scenarios based on total carbon emissions after 2010.

The low estimate was 625 billion tons, the middle was 2,500 billion tons, and the high was 5,000 billion tons.

The Global Carbon Budget estimates that total global carbon emissions in 2022 were 40.6 billion tons. Annual emissions have been close to this figure every year since 2010, so the researchers found that the low-estimate scenario they used was already being emitted.

The team assumes that the middle emission scenario has been reached in about 50 years and the high estimate in just over a century.

“The twilight zone plays an important role in the ocean’s carbon cycle, as most of the carbon dioxide taken up by phytoplankton ends up there when their remnants sink from the sea surface,” study co-author Jamie Wilson, a post-doctoral researcher at the UK’s University of Liverpool, said in one Explanation.

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“One of the challenges in predicting how this carbon movement might change in the future is that there are many processes to unravel in the modern ocean. By looking back at the twilight zone of past warm periods, we can identify the most important processes and use them to predict the future. We have found that this natural carbon cycle is likely to be changing already and may be disrupted long into the future.”

According to the study, the climate crisis has impacted the world’s oceans in the form of pollution, warming, oxygen depletion, acidification and overfishing. These impacts have prompted conservationists to consider various conservation efforts, such as curbing harmful activity in the oceans.

Protecting the twilight zone will be difficult because typical conservation efforts such as preventing fishing or deep-sea mining cannot apply there, Rocha said.

“A marine reserve for the (twilight zone) makes very little sense because the impacts it affects are global in nature,” he said. “What we really need to protect the (Twilight Zone) is to stop, or at least slow, the rapid rate of change we are subjecting our planet’s climate to.”