The Shinkai6500 deep-sea submersible. Photograph: Jon Copley

Told in the first person, we appreciate Jon Copley’s account of his most recent amazing work, and the Guardian’s coverage of it:

Five kilometres, or 3.1 miles, is not a great distance on land – the length of a pleasant stroll. But five kilometres vertically in the ocean separates different worlds. On 21 June I had the opportunity to make that short journey to another world, by joining Japanese colleagues for the first manned mission to the deepest known hydrothermal vents, five thousand metres down on the ocean floor.

The goal of the expedition, led by Prof Ken Takai of the Japan Agency for Marine-Earth Science and Technology, was to study the limits of life at deep-sea vents in the Cayman Trough as part of a round-the-world voyage of discovery by the research ship RV Yokosuka. In February, I had led a British expedition investigating the same vents with a remotely operated vehicle, so I was delighted to join the team actually visiting them inside one of the few machines that can carry people beyond five kilometres deep.

Crammed into the two-metre chamber of the Shinkai6500 with pilot Yoshitaka Sasaki and co-pilot Yudai Tayama, we waited for the team on the deck of the RV Yokosuka to hook us up to the stern gantry and lift us out over the rolling blue waters of the Caribbean. We fanned ourselves as the temperature inside our hollow metal ball rose past 30C in the tropical morning sun. At 09.07 we were lowered gently into the water, detached from the ship, and sank beneath the grip of the waves on our journey into the void below.

Jon and the crew of the submersible during its descent. Photograph: Jon Copley

Five minutes after leaving the surface, we passed 200 metres depth and entered the “twilight zone”, where sunlight is already too dim for microscopic algae to thrive. Our portholes became discs of the deepest blue imaginable – a colour eloquently described as “luminous black” by deep-sea pioneer William Beebe, after whom we named the undersea vents below. Beebe and his colleague Otis Barton were the first people to venture into the deep ocean and see its life first-hand, when they dived in their bathysphere in the early 1930s.

Read the whole account here.