Life in the ocean's twilight zone "could disappear" amid warming seas

Life in the ocean's twilight zone is expected to face dramatic decline and even extinction as seas warm and less food reaches the dimly lit waters. The Twilight Zone lies 200 to 1 meter below the surface and is home to a variety of organisms and animals, including specially adapted fish such as lamprey sharks and dragon sharks, which have huge eyes and glowing, bioluminescent skin. Animals in the twilight zone feed on billions of tons of organic matter, such as dead phytoplankton and fish feces, that drift from the ocean's surface. Drifting particles are known as marine snow. Warmer waters actually reduced the amount of food that sank into the zone, meaning as much as 40% of life in the twilight waters could be gone by the end of the century, according to the study, which was published in Nature. Restoration can take thousands of years. "The rich diversity of life in the twilight zone evolved over the past few million years when ocean waters cooled enough to act more like a refrigerator, preserving food longer and improving the conditions that allow life to thrive," said Katherine Crichton, lead author of the study. and Postdoctoral Research Fellow at the University of Exeter. “According to the studies we have done, 15 million years ago there was not all this life [in the twilight zone], and now, because of human activity, we may lose everything. It's a huge waste of wealth," Crichton told the Guardian. "If we don't reduce greenhouse gas emissions quickly, it could lead to the extinction or extinction of life in much of the twilight zone within 150 years, with knock-on effects lasting millennia." Warmer oceans have also reduced carbon storage, said Paul Pearson of Cardiff University, lead researcher on the study. That's because the "carbon that sinks as part of marine snow" is mostly consumed by microbes closer to the surface, rather than sinking further. Less decline means faster carbon release. Crichton said the good part of the study was that “it doesn't seem like we've reached a tipping point. We can't avoid some losses, but we can avoid the worst if we control emissions." Although poorly understood, the twilight zone "contains probably the largest and most underutilized fish population in the world and recycles [about] 80% of organic material that sinks," according to a UN program that studies the region. Crichton said: "We still know relatively little about the ocean's twilight zone, but we can use evidence from the past to understand what might happen in the future." Her team's findings suggest that "significant changes may already be underway." The study offered three possible futures for the twilight zone: a low-carbon scenario that allows for a total of 625 billion tons of emissions from 2010; the medium scenario, which assumes 2,500 billion tons; and high, which allows for 5,000 billion tons. "If we get to a medium or high scenario, both are very bad news for the twilight zone," Crichton said. To put the emissions data into context, the Global Carbon Budget led by the University of Exeter estimated that in 2022 the total global CO₂ Emissions reached 40.6 billion. tons. Emissions were close to 22 billion tonnes annually between 1940 and 2010, so most CO emissions₂ A low-carbon scenario has already been released in the study. (theguardian)