Humans have sailed the oceans’ surfaces for millennia, but their depths remain effectively uncharted. Only about a quarter of the seafloor has been mapped at high performance. Maps of most regions display only approximate depths and often miss entire underwater mountains or valleys.

So a group of researchers has selected some deep-diving experts: Elephant Seals and Weddell Seals. Scientists have been placing trackers (跟踪装置) on these marine mammals around Antarctica compared these divers’ location and depth data with some of the less detailed seafloor maps. They for years, gathering data on ocean temperature and salinity. For a new study, the researchers spotted places where the seals (海豹) dove deeper than should have been possible according to the maps — meaning the existing depth estimates were inaccurate.

In eastern Antarctica’s Vincennes Bay, the diving seals helped the scientists find a large, hidden underwater valley. An Australian research ship called the RSV Nuyina later measured the valley’s exact depth using sonar (声呐). “The seals discovered the valley, and the ship confirmed it,” says Clive McMahon, a researcher at the Integrated Marine Observing System in Australia and a co-author of the new study.

But seals can’t map the entire ocean floor. The trackers used in the study could mark a seal’s geographical location only within about 1.5 miles, which allows for useful but not exactly high-resolution data. Plus, because the seals don’t always dive to the bottom of the ocean, they can show only where the bottom is deeper than in existing maps — not shallower. McMahon notes that scientists could improve on these data by means of more precise GPS trackers and analyzing the seals’ diving patterns to determine whether they have reached the seafloor or simply stopped going down.

The current seal-dive data can still be valuable for an important task, says Anna Wahlin, an oceanographer at the University of Gothenburg in Sweden. The deep ocean around Antarctica is warmer than the icy waters at the surface, and seafloor valleys can allow that warmer water to flow to the ice along the continent’s coast, Wahlin explains. To predict how Antarctica’s ice will melt, scientists will need to know where those valleys are and how deep they go.

A tiny Alaska village has experienced a boom in tourism in recent years as polar bears spend more time on land than on Arctic sea ice.

More than 2,000 people visited the northern Alaska village of Kaktovik in 2018 to see polar bears in the wild. The far north community lies in an area where increasingly higher temperature has sped up the movement of sea ice, the primary habitat(栖息地) of polar bears. As ice has gradually moved to deep water beyond the continental shelf, more bears are remaining on land to look for food.

Polar bears have always been a common sight on sea ice near Kaktovik, but villagers started noticing a change in the mid-1990s. More bears seemed to stay on land, and researchers began taking note of more female bears making homes in the snow on land instead of on the ice to raise their babies. U. S. Fish and Wildlife Service biologists began hearing reports of the increasing number of polar bears in the area in the early 2000s. As more attention was given to the plight (困境)of polar bears about a decade ago, more tourists started heading to Kaktovik.

The village had fewer than 50 visitors annually before 2011, said Jennifer Reed, of the Arctic National Wildlife Refuge. "Today we’re talking about hundreds and hundreds of visitors, many from around the world each year," Reed said. Most tourists visit in the fall, when bears are forced toward land because sea ice is farthest away from the shore. Bruce Inglangasak, a local hunter who sometimes offers wildlife-viewing tours, said been offering polar bear tours since 2004. Most of his clients(客户) are from China and Europe, as well as from the lower 48 U. S. states. Many tourists stay several days in the village, which has two small hotels. The villagers have benefited a lot from that. In turn, they provide more effective protection for polar bears with financial support from tourism development.

If you were to see the Great Banyan Tree in the Acharya Jagadish Chandra Bose Indian Botanic Garden from a distance, you could be forgiven for mistaking it for a forest. Covering more than 14,493 square meters, the tree is the widest in the world. It is so large that it covers more ground than the average Wal-Mart.

No one is quite sure exactly how old the Great Banyan Tree is due to the lack of official records, but experts guess that the tree is at least 250 years old. The earliest references to the tree have been found in travel writing dating from the 19th century. Over the years, the tree has gone through a lot. Not only has it survived two major disasters in 1864 and 1867, but its main trunk also caught a deadly disease. And because of the disease, the main trunk of the tree needed to be removed in 1925.

Despite going through such a major surgery, the Great Banyan Tree proved resilient (能复原的).This is because of thousands of aerial roots (气生根) that grow from the tree's branches and go into the ground. And that is what gives the impression of a full forest rather than a single tree.

Taking care of this large tree is so difficult that it takes a 13-member team. Not only do they make sure the tree stays healthy, but they also “train” the roots to grow correctly.

In Indian culture, banyan trees are among the most venerated. It is considered to be a sacred tree in various religions. For example, in Hinduism, it symbolizes longevity and represents the great God, Brahma. In Buddhism, banyan trees are also significant because it is believed that Buddha sat beneath one for 7 days.

Want to see the Great Banyan Tree for yourself? The botanical garden is easily accessible by car or bus from the Kolkata city center. As well as the Great Banyan Tree, you can also see a wide variety of plants from all around the world, making it an amazing journey.