SciBar: Beyond the Abyss

The Five Deeps Expedition and Extreme Marine Exploration

Words by Erna Karsono, edited by Nicola Simcock

Have you ever wondered about life beyond the abyss? In his February SciBar talk Dr Alan Jamieson, senior lecturer in Marine Ecology at Newcastle University, shed some (flash)light on the mysterious life in the deepest part of the oceans, the hadal zone. 

The Hadal Zone comprises any part of the ocean deeper than 6,000 metres. Its trenches are formed by tectonic plate subduction whereby a huge part of the abyssal plain (an underwater plain deep on the ocean floor) has been forced downward, up to 11,000 metres in some places. The abyssal plains make up ~45% of the Earth’s surface. The word “hadal” comes from “Hades”, of Greek mythology. It refers to both the kingdom of the underworld and its god. Hades didn’t allow his subjects to leave the kingdom, which gives a fitting analogy for the animals living in the hadal zone, as their travel outside of the deep trenches is limited.

In his fascinating talk Alan told us about his time exploring these depths on his ten month, privately funded, round-the-world expedition: the Five Deeps Expedition. Covering 47,000 nautical miles (87,000 km), and completed in August 2019, it is the first successfully manned expedition to the deepest points of all five oceans.   

The expedition ship DSSV Pressure Drop was originally built for endurance to hunt Russian submarines in the cold war but has since been refitted for research and exploration. Specialist changes were made specifically for the expedition such as padding the engines with rubber blocks to reduce noise, allowing communication between the onboard and underwater crews. Additionally, the main deck has both a wet and dry laboratory for experiments and the onboard facilities provide comfortable accommodation for up to 49 crew members.

The deep dives themselves were completed in Limiting Factor, a titanium submersible big enough for two, with three viewing ports for observation. Limiting Factor or ‘LF’ is designed to descend to 11,000 metres in less than 3.5 hours ─ which is really fast in submersible terms! It is currently the only submersible in existence that can reach the earths deepest trenches and has been commercially certified for safety. As Alan pointed out, the submersible has undergone such rigorous safety testing that diving to a depth of 11,000 meters actually requires fewer risk assessments than hiring a university minibus! The Five Deeps Expedition accomplished 39 dives in total and the LF became the first submersible to reach Challenger Deep on more than one occasion. In addition to the submersible, three remote controlled landers – Flare, Skaff and Closp – were deployed 103 times to monitor, record and retrieve samples from the deep sea. Prior to the submersible and landers being deployed, a multibeam sonar and echo sounder Kongsberg EM124 provided detailed and accurate images mapping the seafloor.

During the talk Alan wowed the audience with a steady stream of newly discovered fish and cephalopod species. His videos demonstrate how hadal zone animals survive the extreme pressure of the deep sea. The near freezing temperatures, low food supplies, volcanic activity and lack of light can lead to some interesting adaptations. For example, the bodies of some species are made of a gel-like substance instead of muscle due to the scarcity of food and the beneficial hydrodynamic properties.

Below are a few observations of the Hadal zone fish caught on camera miles beneath the waves: 

  • Snailfish – a very common family of fish in the Hadal Zone. These gelatinous fish are tiny, translucent and sometimes pinkish. The Mariana snailfish is the deepest fish in the world.
Notoliparis kermadecensis 7166m Kermadec Trench_Snailfish
  • Cusk-eels (robust Assfish – its real name we swear!) – an eel-like fish species 
Cusk Eels
  • Tunicate ascidian (sea squirt) – are anchored above the seafloor to avoid being engulfed by seismic induced sediment slides.
  • Cutthroat eel – a very common family of fish in the hadal zone.
  • Amphipods – usually tiny crustaceans, but one species is known as a ‘super giant’. It has a massive, but empty, body thought to have evolved to make potential predators think it is much bigger and scarier than it actually is.
Amphipod from 8000 metres
Amphipod in Hand

Sadly, even at the isolated ocean depths human activity is glaringly evident, with pollution rife. The most conspicuous things discovered in the Puerto Rico trench were magazines, coke bottles and beer bottles, amongst others, littering the seabed. From such observations Dr Jamieson and colleagues have previously published a study demonstrating how widespread microplastics are across deep-sea species. Alan also highlighted their persistence, as one pollutant was a banned organic contaminant invented and used in the 1950’s and 1960’s. For more information see:

But there are plenty of positives from this incredible expedition to balance things out. Many new species have now been discovered in the hadal zone with our knowledge of the deep sea massively expanded. As a result of this expedition we now know that some deep-sea animals, such as super giant amphipods, the red prawn and cusk-eel, occupy a larger living territory than any animal on land, which will have huge ecological implications. Additionally, studying the variety of similar species at the trenches, thousands of miles apart, can further advance our knowledge of evolutionary biology.

Following an extended round of questions from our audience Alan informed us that his deep-sea adventures are far from over. His next expedition will once again see him climb inside Limiting Factor to explore the Ring of Fire in the Pacific Ocean. We wish him the best of luck and can’t wait to hear about what he finds!

Further information can be found at  

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