The twilight zone (朦胧地带) contains the largest and least explored fish stocks (储备) of the world’s oceans. Ranging from just below 200 metres to 1,000 metres deep, it is an interface between the well-studied sea life in the sunlit zone above and the ecosystems of the darkest territory below. It has a major role in removing carbon dioxide from the atmosphere and storing it for centuries or longer. The twilight zone is also known to the largest migration on Earth. Huge numbers of fishes and zooplankton (浮游动物) move hundreds of metres towards the surface each night to feed, before withdrawing back down at dawn.

Yet the zone is poorly understood — physically,     biogeochemically and ecologically. Even the number of organisms that live there remains a mystery, let alone their diversity and function.

It is alarming, then, that this vast ocean domain is at risk in three ways-even before any of the potential consequences are understood. First, the world’s growing population has an increasing need for food. Second, sea-floor mining for minerals and metals could release waste into the region. And   third, climate change is varying temperature, acidification and oxygen levels in ways that are likely to affect life there.

The twilight zone is hard Io study. Its organisms are difficult to sample and analyse, being thinly distributed, almost invisible and often fragile. They also live at pressures of up to 100 atmospheres, which poses problems for laboratory-based investigations.

Critics might argue that walers near coasts and above shelves are more deserving of study, given the huge environmental pressures there, as well as their importance to societies. And, of course, they need attention. Sadly, however, it is too late to avoid widespread environmental damage to these inshore regions. Instead, research efforts and local policies must aim at minimizing the worst effects.

By contrast, the twilight zone is almost left in its original condition. Moreover, the majority of it lies beyond national administration. This makes it of common interest and responsibility, and means that global agreement is necessary to manage it.

Scientists have discovered an underwater coral tower near the Great Barrier Reef(大堡礁) that’s taller than New York’s Empire State Building. It’s the tallest underwater structure discovered in over 120 years.

The researchers who discovered the reef were on a year-long trip aboard the Schmidt Ocean Institute’s research ship Falkor, where they were working to map the sea floor around Australia.

The scientists used a special underwater robot called SuBastian to help them explore and develop 3D maps. In late October, as part of their exploration, the team came across the tower. It’s known as a “detached reef”, since its structure isn’t attached to the Great Barrier Reef, but rises on its own from the sea floor.

At the bottom, the tower is nearly a mile wide. But from there, it becomes much more narrow, rising 1,640 feet and stopping just 130 feet below the surface of the ocean. The lower is one o£ eight similar towers near Northern Australia’s Cape York Peninsula. The other seven towers were discovered in the 1880’s.

“It’s a big reef not to have known about,” said Tom Bridge, “What it highlights is how little we know about the ocean, even the Great Barrier Reef. The Great Barrier Reef is bigger than many European countries and that only a small part of it is made of the shallow water reefs it’s famous for.”

Overall, the Great Barrier Reef is struggling. Recent studies have shown that about half of its corals have died in the last 25 years, in part because of rising ocean temperatures due to the climate crisis. Over the last year, the Falkor’s scientific team has discovered 30 new kinds of sea creatures. In March, they discovered what they believe is the longest sea creature ever recorded. The animal is called a “siphonophore” and it’s 150 feet long.

The grass swung gently above a crack in the limestone (石灰岩) and Ludvik Husu realized he had found what he was searching for: a new cave in Slovenia’s dramatic Karst (喀斯特) region.

The cave enthusiast, with more than 50 years of experience, told AFP that “the conditions were perfect ... all the signs pointed to something beneath” as he felt the air current push up from below.

The 63-year-old had come across a new, 60-meter-deep limestone cave, a discovery that made the headlines this summer in a country that prides itself on its 14,000 underground caves.

The tiny Alpine nation is unusually rich in caves, which are a major tourist attraction. Perhaps the best known is the Postojna cave system, the longest in Europe, discovered by another amateur enthusiast two centuries ago. It extends for 24 kilometers and has offered up valuable finds for biologists.

Stanislav Glazar, a Postojna cave guide, told AFP that more than 150 species have been discovered in the system.

Glazar said Postojna is one of the richest caves in the world “in limestone formations.” The cave, located about 50 kilometers south of the capital Ljubljana, was also home to the world’s first cave tourist train, which began transporting visitors in 1872.

Elsewhere in the Karst region, the cave systems are of historical, cultural and even extraterrestrial interest. For instance, the UNESCO-listed Skocjan system was where the European Space Agency sent some astronauts to prepare for life in space.

“Astronauts know that the Karst world is exceptional, in a similar way to the environment in space: you don’t know what to expect at your next step,” said Skocjan Caves director Tomaz Zorman.

But for Husu, it’s the exploration that proves most rewarding. Once he knows there is something beneath, he digs around the crack to widen it and alerts fellow cavers to help gain access. He then uses ropes and a lamp to go down to what are vertical entrances in most caves. But doesn’t he feel scared to enter such unexplored depths?

“You enter a cave out of curiosity — there is no fear! Those who feel fear should stay home,” he said.