🗺️ Mapping and exploring the ocean

Scientists mainly use sonar, sending sound waves down from a ship and carefully measuring how long each echo takes to bounce back off the seafloor, to calculate the exact depth and shape of the ground far below the surface. By sailing back and forth across an area and combining thousands of these individual depth measurements together, scientists can build an incredibly detailed map showing underwater mountains, deep trenches, and flat plains hidden beneath the waves. Even with modern technology, a surprisingly large portion of the ocean floor remains completely unmapped in fine detail, since mapping the whole ocean thoroughly takes an enormous amount of time, ships, and effort.

A submersible is a small, specialised underwater vehicle built to carry a few people or scientific equipment very deep underwater, often much deeper than a regular submarine is designed to safely travel. Unlike large military submarines, which can operate independently for long stretches, most submersibles rely on a support ship at the surface to lower them down, keep track of their location, and bring them back up again afterward. Because deep ocean water pressure increases enormously the deeper you go, submersibles built for the very deepest ocean trenches need incredibly strong, carefully engineered hulls to protect the people or equipment safely inside.

The ocean is absolutely enormous, covering most of Earth's surface, and much of it is also incredibly deep, dark, and under crushing water pressure, all of which makes exploring it far more difficult and expensive than exploring most places on land. Special equipment, like pressure-resistant submersibles and advanced sonar, is needed just to survive and see anything at all in the deepest parts of the ocean, and building and operating that equipment costs an enormous amount of money and expert planning. Because exploring the deep ocean is so slow, expensive, and difficult, scientists tend to focus carefully on specific interesting areas one at a time, rather than trying to map or explore the entire ocean all at once.

Scientists sometimes attach a small, harmless tracking tag to a whale's skin, which sends location signals up to satellites as the whale swims, letting researchers follow its exact journey across thousands of kilometres of open ocean. Researchers also identify individual whales by unique natural markings, like the distinctive pattern on a whale's tail fluke, which lets them recognise and follow the very same whale across different sightings, sometimes even years apart. By combining tracking data from many different whales over many years, scientists have mapped out detailed migration routes, showing how whales travel between feeding grounds near the poles and warmer breeding grounds closer to the equator.