Life in the ocean’s “twilight zone” is threatened by climate change

(CNN) One of the largest habitats on Earth could see its rich diversity of life diminished by the end of the century due to the climate crisis.

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

The marine area, which accounts for nearly a quarter of the ocean’s volume, is home to billions of metric tons of organic matter and some of the most amazing biodiversity on Earth, despite being out of reach of sunlight.

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

The tiny crustacean known as Megacalanus princeps lives in the ocean’s twilight zone at a depth of 1,000 meters in the northeastern Atlantic Ocean.

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

ancient warm oceans

Paleontologists and oceanographers have collaborated to study the impacts on the ocean’s aurora zone during ancient warming events in order to predict how habitats will 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, calcium carbonate shells accumulate 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.

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Detailed study results were Published Thursday in the magazine Nature Communications.

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

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

“We found that the Twilight Zone was not always a rich, life-filled habitat,” study co-author Paul Pearson, professor emeritus at Cardiff University in the UK, said in a statement. “In these warm periods, the number of organisms living in the twilight zone was much lower, because much less food arrived from the surface waters.”

Particles of organic matter from the ocean surface drift downward and serve as one of the main food sources for life in the aurora zone. But previous warming events caused bacteria to decompose more quickly, so few made it to the ocean area.

Warmer ocean temperatures also increase the metabolic rates of organisms, which leads to an increase in food demand and oxygen consumption, according to the study.

“The rich diversity of twilight zone life has evolved in the last few million years, when ocean water cooled enough to act like a refrigerator, preserving food for longer, and improving conditions that allow life to thrive,” Crichton said.

Louise A. Rocha, curator and Follett Chair of Ichthyology at the California Academy of Sciences, is worried about undetected changes because the aurora zone has not been well studied, largely due to the disconnect between funding and the costs of exploring this. region.

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Rocha, who was not involved in the study, is looking at the aurora zone and the mesozoic region directly above it, located between 98 and 492 feet (30 and 150 meters) below the surface.

“There is no baseline data to compare what we measure, so this study that looks at the formation of the fossil record over time is one of the few ways we can try to understand how we cause the aurora zone to change,” Rocha said.

Predicting the future

Based on what they found from ancient warming events, the researchers combined this data with Earth’s System Position Simulation – 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 that might change in the future over decades, centuries and even millennia as the world warms.

“Our findings suggest that significant changes may already be underway,” Crichton said. “Unless we quickly reduce greenhouse gas emissions, this could lead to the disappearance or extinction of much of life in the Twilight Zone within 150 years, with effects extending into thousands of years after that. Even a low-emissions future could have a significant impact, but this will be much less severe.” from medium and high emissions scenarios.Our study is the first step to discovering the vulnerability of this ocean habitat to climate warming.”

The researchers used three emissions scenarios based on total carbon dioxide emissions after 2010.

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

The global carbon budget estimates that total global carbon dioxide emissions in 2022 were 40.6 billion metric tons. Annual emissions have been close to that number every year since 2010, so the researchers note that the low-estimation scenario they used did indeed emit.

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The team believes that an intermediate emissions scenario will be reached in about 50 years, and the high estimate in just over a century.

Study co-author Jamie Wilson, a postdoctoral researcher at the UK’s University of Liverpool, said in a statement.

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

The climate crisis has affected Earth’s oceans in the form of pollution, warming, deoxygenation, acidification and overfishing, according to the study. These effects have prompted conservationists to consider various prevention efforts, such as restricting harmful activities in the oceans.

Protecting the Twilight Zone will be difficult, Rocha said, because typical conservation efforts, such as banning deep-sea fishing or mining, cannot be applied there.

“A marine protected area in the ‘Twilight Zone’ does not make 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 dramatic rate of change that we’re undergoing on our planet’s climate.”

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