Life in the ocean’s ‘twilight zone’ could disappear due to the climate crisis | CNN

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One of the Earth’s largest habitats could experience a decline in its rich diversity of life by the end of the century due to the climate crisis.

The mesopelagic zone of the ocean, also called the “twilight zone,” is located from 656 feet to 3,280 feet (200 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 metric tons of organic matter and some of Earth’s most stunning biodiversity, despite being inaccessible to sunlight.

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

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

Paleontologists and ocean scientists teamed up to study the effects on the ocean’s twilight zone during past ancient warming events to predict how the habitat may respond in the future due to global warming. The research team studied cores taken from the sea floor that contained evidence of preserved microscopic shells of plankton.

Over time, shells of calcium carbonate build up on the sea floor, preserving information about what the environment was like during their lifetime. The tiny shells effectively create a timeline of how the ocean has changed over millions of years.

A study detailing the findings was 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 may happen in the future,” said lead study author Dr. Katherine Crichton, a postdoctoral researcher at the University of Exeter in the UK. Kingdom, in a statement.

According to the study, the researchers focused on two warm periods that occurred 15 million years ago and 50 million years ago, where even ocean temperatures were “significantly warmer than today.”

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

Particles of organic matter from the surface of the ocean drift down and serve as one of the main sources of food for life in the twilight zone. But past warming events caused the material to break down faster in bacteria, so less of it reached the ocean region.

According to the study, warmer ocean temperatures increase the metabolic rate of organisms, resulting in increased demand for food and oxygen consumption.

“The diversity of life in the twilight zone evolved over the last few million years when ocean waters cooled enough to act as a refrigerator, preserving food longer and improving the conditions that allowed life to thrive,” Crichton said.

Luiz A. Rocha, California Academy of Sciences curator and Follett Chair in Ichthyology, worries that changes are occurring that are not being detected because the twilight zone is so understudied, largely because of the lack of connection between funding and the cost of that research. county

Rocha, who was not involved in the study, studies the twilight zone and the mesophotic zone just above it, which is between 98 and 492 feet (30 to 150 meters) below the surface.

“There’s no baseline data to compare what we’re measuring against, so this study, which looks at the composition of the fossil record over time, is one of the few ways we can try to understand how we’re causing the twilight zone to change.” Rocha said.

Based on what they discovered from ancient warming events, the researchers combined this data with Earth system mode simulations – Modeling the Earth’s carbon cycle as it moves through the land, sea and atmosphere.

The team’s work revealed what is currently happening in the twilight zone and how it could change decades, centuries and even millennia into the future as the world warms.

“Our findings suggest that significant changes may already be occurring,” Crichton said. “If we don’t rapidly reduce greenhouse gas emissions, it could lead to the disappearance or extinction of much of the twilight zone life within 150 years, with consequences thousands of years later. Even a low-emissions future could have significant impacts, but they would be much less severe than medium and high emissions scenarios Our study is the first step in understanding how vulnerable this ocean habitat may be to climate warming.

The researchers used three emission scenarios based on total carbon dioxide 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 dioxide emissions in 2022 were 40.6 billion tonnes. Annual emissions have been close to that number every year since 2010, so the researchers noted that the lower-end scenario they used has already emitted.

The team believes that the average emissions scenario will be achieved in about 50 years, but the highest 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 as their remains sink from the surface ocean,” said study co-author Jamie Wilson, a postdoctoral researcher at the UK University. In a statement from Liverpool.

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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 that need to be disentangled in today’s ocean. By looking back at the twilight zone in past warm periods, we can identify the most important processes and use them to predict the future.” We found that this natural carbon cycle may already be changing and may be disrupted long into the future.

The climate crisis has affected the Earth’s oceans in the form of pollution, warming, deoxygenation, acidification and overfishing, according to a study. These consequences have led conservationists to consider various conservation measures, such as limiting harmful activities in the oceans.

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

“A marine protected area (twilight zone) makes very little sense because the impacts that affect it are global in nature,” he said. “What we really need to protect (the twilight zone) is to stop or at least slow down the high rate of change that we are subjecting our planet’s climate to.”