Oceanographer Dawn Wright: ‘When we reached the bottom, we saw a beer bottle’

The American oceanographer Dawn Wright is the first Black person and only the 27th human to have been to the deepest spot on the planet. Challenger Deep, at the southern end of the Mariana Trench in the western Pacific Ocean, is 10.9km (6.8 miles) below sea level – deeper than Mount Everest (8.8km [5.5 miles]) is tall. Wright’s summer 2022 descent is documented in a new book, Mapping the Deep , written with her input. The dive was undertaken in a two-person submersible called Limiting Factor owned (since sold) by Caladan Oceanic , an ocean expedition company founded by investor turned deep sea explorer Victor Vescovo , who was also the craft’s pilot. Wright, 63, who also goes by the moniker “Deepsea Dawn”, is the chief scientist of Esri, a multinational that makes geographic information system (GIS) software for mapping and spatial analytics.

Sending people to the deep ocean can be dangerous because of the extreme underwater pressure. Last year , OceanGate ’s Titan submersible imploded on a journey to view the wreck of the Titanic , killing all five passengers on board . Why not just leave it to robots?
Most of the exploration in the ocean is done by robots – it’s just more efficient, especially for mapping. But occasionally, it is important for a human to go down. It can be the way to get the best understanding of how a particular part of the Earth is working or solve a scientific mystery. In the case of Challenger Deep it is an iconic place and we had a scientific mission.

OceanGate didn’t take proper safety precautions . The sub wasn’t certified, and the hull was cylindrical and made of carbon fibre. The sub I went down in had a hull machined to be as close to perfectly spherical as possible – it is the geometry that protects you from hydrostatic pressure – and it was made of titanium – the strongest material for the purpose. It was also certified: I wouldn’t have gone otherwise.

What was the scientific point of your trip?
Challenger Deep is made up of three depressions and my dive was to the least visited, Western Pool. We were the first to set eyes on some of the ground we covered.

We saw anemones, sea cucumbers, amphipods – all withstanding huge pressure and functioning in complete darkness and cold

On the engineering side, it was to test a prototype instrument: a portable sidescan sonar specifically designed to withstand pressure and work at any ocean depth.

Then we undertook multibeam sonar mapping from the support ship to give us a fresh map of the entirety of Challenger Deep and the Mariana Trench. That data has been deposited with Seabed 2030 , a global collaborative effort to completely map the seabed by 2030 which Esri is part of.

What was the dive like and what did you see?
It was about a 10-hour round trip with two-and-a-half hours at the bottom to observe and test the prototype instrument, which we did over an area of a few hundred square metres. The spherical cockpit is a tight space and Victor and I sat with everything that we needed within reach. There is no toilet, so I had to safely dehydrate before the dive.

At around 1,000m you get into complete darkness. Through the sub’s portholes, we saw bioluminescent jellyfish and worm-like siphonophores, which flashed back at us when Victor flashed the sub’s lights on them. The first moments of reaching the bottom were disheartening – we saw a beer bottle – but the rest was wonderful. We observed vast fields of boulders: evidence of the two tectonic plates that are colliding in that zone (the old, heavy Pacific Plate is diving underneath the Philippine Sea Plate). And we saw tiny creatures such as anemones, sea cucumbers and amphipods [a type of crustacean] – all withstanding huge pressure and functioning in complete darkness and cold. Our images and samples are being studied by marine biologists.

Your career includes over 20 ship-based research expeditions and dives in other submersibles . You have also pioneered the application of GIS to seafloor and ocean mapping. What got you interested in ocean science?
I grew up in the Hawaiian islands and I was always at the beach. But I became fascinated by the geology too: living somewhere that started off as volcanoes under the sea and then rose. Combine that with watching Jacques Cousteau on TV and reading ocean adventure books and I made the decision at age eight to become an oceanographer.

My first submersible dive was in 1991 in a research vessel called Alvin. It was to make observations of the geology and biology and map the distribution of hydrothermal vents (undersea hot springs) in a segment of the East Pacific Rise, the seafloor spreading zone in the Pacific Ocean. It was one of the first studies applying GIS to seabed mapping anywhere. You can get lost in a map of the ocean floor.

I worry deep-sea mining would be massively damaging to large parts of the seabed which are habitats to all sorts of biota

One of your bugbears is that so little of the seafloor has been mapped to date in high resolution. Is it really that bad?
Yes! Our current collective estimate is that we have 26.1% of the ocean mapped to the modern detail that we need. That’s a lot we don’t know about our home, given about 70% of our planet is ocean.

The longer it takes for us to map all the seabed in detail, the more we play with fire: it is vital for so many things. For example, it gives us a better understanding of ocean volume, enabling climate scientists to build better models of climate change, improves our predictions of how tsunamis will behave and enables the design of protected marine habitats.

Interest is growing in deep-sea mining . The International Seabed Authority plans to release regulations on the practice next year while Norway is pressing ahead with opening its own waters. Can deep-sea mining be done sustainably? Won’t better mapping of the seafloor aid mining companies to pursue extraction?
The Seabed 2030 data is unlikely to be fine-grained enough for a mining operation. But the project’s data is open: anyone can use it. If mining companies are doing their own mapping of the seafloor, my hope is they would be willing to contribute it to Seabed 2030 to speed up ocean mapping and benefit us all.

At this point, I don’t think it is possible to do it sustainably. The environmental assessments aren’t done and many of us don’t trust that they will be done properly. I have, in my personal capacity, signed a statement from marine experts calling for a moratorium while potential impacts to the ocean environment are studied. I worry it would be massively damaging to large parts of the seafloor which are habitats to all sorts of biota.

What would you like young women of colour who want a career in ocean science to know?
That this type of work is for them too! And that there are organisations that support Black marine scientists that weren’t there when I was coming along. All young people should pursue what they love and not let others divert them from that path. I was told once I was not cut out to be an oceanographer: I’m glad I didn’t follow that advice.

• Mapping the Deep is published by Esri Press (£19.99). To support the Guardian and Observer order your copy at guardianbookshop.com . Delivery charges may apply. The book’s companion website, with a Lego video illustrating Dawn Wright’s dive, is here