Expedition to the Pacific deep sea reveals extraordinary creatures never seen before

In the abyssal Pacific there is a greater biomass of life in the top one centimetre of a given area of seafloor mud than in the entire 4,000 metres of water above it. This can seem surprising at first, given there is no sunlight at those extreme depths and the temperature is a frigid 1.5°C.

But there is a relatively simple explanation: things denser than water such as dead algae, animals and their poop, sink. This is what we somewhat whimsically call “marine snow”. An endless dark snowfall forming the vast drifts of abyssal muds that characterise our planet.

At some places in the middle of the Pacific Ocean geologists have measured the age of the deep sediment layers at 180 million years old. That means marine snow was falling in these parts of the ocean when Diplodocus was browsing on ferns and Ichthyosaurs were swimming the waters above.

That is an extraordinarily long snowfall, and a reminder of just how old some of our ocean basins are.

The region of the Pacific is part of what is known as the Clarion-Clipperton Zone (CCZ), a vast region that covers the same area as most of the continent of Australia. This area contains a vast deposit of polymetallic nodules, which are potato-sized mineral accretions that are gaining attention for the role they might play in the transition to green technology.

The early explorations of the CCZ were focussed on these nodules as a potential mineral resource, but this over-looked an astonishing level of life that thrives at these depths.

A vast amount of time, and a vast amount of space, are clues to answering the paradox in deep sea biology of why are there so many deep-sea species.

We can forgive the first collectors in the CCZ for ignoring all this life – on first glance a typical view of the seabed at 4000 metres looks completely barren. But as is always the case, when we look more closely we find things.

Tiny sponges and bryozoans just a few millimetres in size grow on the nodules. In the mud between the nodules, small crustaceans, worms and molluscs are surprisingly diverse. Drive across the seafloor in a robotically-controlled submarine and after some time, you find larger animals too.

Here is a selection of some of the astonishing life that was found during the latest SMARTEX expedition to the CCZ. Some of these animals have been slowly persisting in the depths of the Pacific Ocean for potentially hundreds of years, from the Barbie-piglet sea cucumber to intricate, beautiful glass sponges.

Find out more about how our scientists are helping tackle the problem of resourcing the green economy in Episode 9 of our Our Broken Planet: The podcast, available to listen now.