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.
