Simon Mitchell: diving deeper

The Pearse Resurgence is an icy spring, emerging beneath an overhang at the base of a steep-sided valley two hoursʼ walk, or a shortish helicopter ride, into Kahurangi National Park, west of Nelson.

The room-sized pool conceals a complex network of caves, which extend far beneath the forested mountains and are occasionally visited by extreme cave divers.

This is where Professor Simon Mitchell, head of the Universityʼs anaesthesiology department, has often returned with his technical-diving buddies, ‘the Wetmulesʼ – so called, because they are stubborn, frequently wet and haul heavy loads of diving gear in miserable conditions.

In 2023, Simon and the Wetmules attempted a world-first dive using hydrogen as a breathing gas at the Pearse, which is now the subject of a documentary, Deeper, currently screening on Netflix.

In the documentary, we see the divers enter the underwater cave system and follow the line into Nightmare Crescent, then drop 100 metres before following a shaft further down, passing through chambers with names like Stantonʼs Hole and Well of Our Souls.

It is terrifying to watch on screen, but Simon denies being courageous.

“I donʼt think Iʼm a particularly brave person, but Iʼm confident in what Iʼve learned over the years and the training and experience that Iʼve had. It doesnʼt feel like a brave thing to jump in the water and go really deep. It just feels like something I do.ˮ

In the aftermath, Simonʼs research team (including University research fellows Drs Hanna van Waart and Xavier Vrijdag) has gained close to $1 million of funding to test the addition of hydrogen to the diverʼs gas mix for ultra-deep diving.

Hydrogen is slightly narcotic, so Simon will conduct further work on whether it could calm a neurological tremor that can affect divers when they exceed depths of around 180 metres.

The self-appointed ‘guinea pigʼ for the Pearse hydrogen dive was fellow anaesthetist Dr Richard ‘Harryʼ Harris, hero of the Thai cave rescue of 12 schoolboys and their coach. Harry had reason to trust Simon if things went wrong: Simon is listed on Expertscape, a global directory of scientists, as the number-one expert worldwide in decompression sickness, or ‘the bendsʼ.

“Simon is one of the most experienced technical divers there is, and has a planet-sized brain,ˮ says Harry in Deeper.

This year, Simonʼs dive-medicine research has been acknowledged with a prestigious award from the Academy of Underwater Arts and Sciences, the NOGI Award 2026 for Science. Previous winners have included Jacques Cousteau; Bob Ballard, who discovered the wreck of the Titanic; and director James Cameron, who said it's harder to get a NOGI than an Oscar.

Notes Simon: “Iʼm not sure I believe that, but it is cool to be recognised.ˮ
In 2015, Simon was also named Rolex Diver of the Year.

During the experiment documented in Deeper, at 200 metres down in the Pearse cave system, Harry turns the switch to breathe the hydrogen, and the tremor he has already experienced subsides.

On the return journey, there is – spoiler alert – an emergency, when breathing gear floods, and Simon manages the surface response with an apparent cool head. He is used to managing life and death in his work as an anaesthetist, but this is on a whole other level.

“You have this massive sense of responsibility with no option to intervene,ˮ he narrates on the documentary during a period when the divers are ultra-deep with no communication. When the emergency unfolds, he sends divers down with fresh gas tanks and narrowly avoids a terrible conclusion.

Another leading-edge experiment has taken Simon and Harry to the Caribbean this year. The pair are taking blood samples from four elite breath-hold divers at the bottom of an 80-metre dive and then again at the surface before the divers take a breath. It is hoped the data from this experiment, funded by a US philanthropist, will help prevent a deadly syndrome where breath-hold divers, even snorkellers, pass out when they reach the surface.

Simonʼs passion for diving started at school while his family were living in Seatoun, on Wellingtonʼs South Coast. “It was just what the kids did in that suburb. We were interested in snorkelling and spearfishing. But not all of them fell in love with it.ˮ

Simonʼs first degree, from Central Institute of Technology, was in marine biology and he worked as a science technician before heading back to university. “It wasnʼt until I was 26 that I knuckled down, got into med school and came to the University of Auckland,ˮ he recalls.

He always maintained his “whole diving passion thingˮ. After completing his medical degree he joined the Navy, with a view to specialising in dive medicine working with the late Professor Des Gorman, who supervised Simonʼs PhD. However, Simon discovered that it was virtually impossible to make a career out of dive medicine, even in the Navy.

So, after about eight years, he left and trained in anaesthesia. “Itʼs a very compatible specialty, partly because the physiology is similar and you learn a suite of interventional skills that make you a very good candidate to have around if something goes wrong on a diving expedition.ˮ

Simon now spends three days a week in the operating room and two days a week at the University, on teaching and research, most of the latter diving related. “Weʼve really found the edge and pushed it in diving activities and in diving research.ˮ

In 2002, Simon did the then deepest-ever shipwreck dive, which was to the wreck of the AHS Centaur, 175 metres deep off the coast of Australia, near Brisbane.

“It was a big deal because it was a substantial historic event when the Centaur, a hospital ship, was sunk by a Japanese submarine in 1943. Two-hundred-and-sixty-four Australian servicemen and women died, mostly medical people.

“That wreck had never been dived, and it had never been confirmed as the Centaur, and we actually found it was the wrong wreck.ˮ

Subsequently, the actual wreck was found not far away but two kilometres deep, over the edge of the Continental Shelf.

It was one of Simonʼs many shipwreck dives, which have led to some scary experiences. “One of the dangers with shipwrecks is that the water is nice and clear, as you go inside, but the wrecks are very silty, and itʼs very easy to stir up the silt, and then you cannot see a thing and get lost and trapped. People die that way.

“Not trying to blame shift, but, on one or two occasions, people have come in behind me and stirred the silt up.

“You just canʼt find your way out, and you can feel the panic rising. You have to control that and tell yourself, ‘If I panic, Iʼll die, simple. If I donʼt panic, thereʼs a good chance Iʼll be able to find my way out of hereʼ and that has been whatʼs happened.ˮ

Other commitments involve editing the top academic journal in the field, Diving and Hyperbaric Medicine, and he has co-written the hyperbaric and diving-medicine chapter in four editions of the revered text Harrisonʼs Principles of Internal Medicine.

Life at home in the Waitākere Ranges is shared with his wife Sian, a nurse manager, and a menagerie that includes chickens and two pugs.

The total dedication has all been worth it. “The amazing places Iʼve been, the people Iʼve been with, the sights that Iʼve seen underwater, I would consider it collectively, a massive highlight of my life.

“This whole world that right from being a little kid has fascinated me – I just enjoy it.ˮ

– Jodi Yeats