The deep ocean remains one of the most mysterious places on Earth. Only around 20% of the ocean floor has been mapped to modern standards. That includes Challenger Deep in the Mariana Trench near Guam, which at around 11,000 metres below sea level is the deepest known point on the planet.
This area is so difficult to get to that just 23 people have taken the plunge since 1960. On 12 July, Dawn Wright, a marine geologist and chief scientist at Esri, a mapping-software company in Redlands, California, became the first Black person to visit. Wright was part of a two-person dive aboard the submersible Limiting Factor, piloted by Victor Vescovo, explorer and founder of ocean research firm Caladan Oceanic in Dallas, Texas.
Shortly before heading out to sea, Wright spoke to Nature about the historic dive and why mapping the depths of the ocean matters.
There have been other trips to Challenger Deep. What will we learn from this dive?
When people get a chance to descend to Challenger Deep, they go to the eastern pool, where the records are set in terms of the absolute deepest points in the ocean. But there are two other depressions, the central and western pools. What we would like to do is use the submersible to get a detailed map of those areas, which has never been done before.
Other dives have been able to generate colour-coded contour maps, similar to what you might use on a hike. What we want to do is generate the equivalent of an aerial photograph. That map is going to look different. It’s going to be a series of grey shades that will show you the structure of the bottom, rather than the specific depths.
We are testing out a new side-scan sonar. It was used recently to locate the world’s deepest-known shipwreck [the USS Samuel B. Roberts, a ship from the Second World War]. It’s a bit of an experiment because this particular instrument has never been used below 6,000 metres.
The entire trip takes around 12 hours. What will you be doing during that time?
So the first four hours is descending. Then it will take another four hours to get back up. The real crucial piece is the four hours in between, when we will be doing our operations. With any type of mapping of an area, we ‘mow the lawn’ so to speak, going back and forth until we have covered the whole area.
Why is mapping the ocean so difficult?
The crux of it is that we have to see through water. It’s actually easier to map other planets. Those sensors use electromagnetic energy, which can move through the atmosphere and space with no problem. That same energy is not nearly as effective when you try and shoot it through water. So we have to use sound energy instead, and we have to go to sea to do that. We do not yet have a satellite in space that uses acoustic sensing and can give us the same coverage to map wide swaths of this planet.
Why hasn’t mapping with side-scan sonar been done before at Challenger Deep?
The emphasis during other dives has been on biology — and for good reason. It’s led to the discovery of new species, like Eurythenes plasticus, which is a species of amphipod [crustacean] so named because it has microplastics [a type of human-made pollution] in its tissue. It’s the first species to be discovered with plastic already a part of its biology, which, to me, is so tragic.
So findings in the deep ocean tell us something about Earth’s health?
Challenger Deep is a cautionary tale. What we do on land and to our atmosphere will eventually affect every part of the planetary system. And then, there’s what the ocean gives us — it absorbs 90% of the heat that we generate and 25% of our carbon dioxide emissions. In terms of climate change, the ocean is buying us time.
One of the reasons why mapping the ocean floor matters is that we’re not going to really understand the distribution of heat in the oceans until we understand the ‘bathtub’ that contains the water. Heat circulating through the oceans eventually gives us our daily weather and our long-term climate.
What are the risks of diving so deep?
The deepest ocean is a place that is extremely dangerous. The pressure down there is 16,000 pounds per square inch [more than 1,080 atmospheres]. It’s near freezing and completely dark. If anything goes wrong with the submersible, the implosion will kill us in a nanosecond.
So that leads to a question I’m often asked — are you afraid? My answer is no. I put my faith completely in this technology and in Victor’s skill in operating it.
Some researchers say we should send robots, instead of humans, to the ocean’s depths. What do you think?
There’s certainly room for both. I’m so glad to hear that there are robots able to scan many, many parts of the ocean. We need more of those types of vehicle. But there’s still nothing like sending a human, with our decision-making ability, and with what we can see through human eyes. We need to continue to do that, when and where we can.
You are about to join a select group of deep-sea divers. What would your child-self say about this?
Child-me would have been like, “Yeah!” I grew up reading about people who went to sea, especially pirates. So my first goal was to go to sea. That dream was fulfilled in the 1980s, and it’s total icing on the cake to be able to go to Challenger Deep. It’s just blowing my mind.
I am also trying to take the opportunity to express what this means to me as the first Black person to make this dive. I wish this wasn’t such a big deal — but it is, especially in the wake of George Floyd’s murder. I want young people to see that this is possible for them, and that it’s not off limits because they are Black.