Vanishingly little sunlight manages to find its way through the twilight zone. Situated between 100m and 1,000m beneath the surface of the ocean, these gloomy depths are a mysterious place: cold and dark, unfriendly and inhospitable.
It’s not just the lack of light that means we know relatively little about what lives and dies down there. Satellites can only tell us what is happening on the surface of the seas, and instruments moored to the bottom give us information only about the ocean floor.
To find out more about what lies between therefore means going on research expeditions. I’ve just returned from one to South Georgia, where I spent months in the choppy waters of the South Atlantic.