If you’ve ever allowed yourself sink to the bottom of a swimming pool, you’ll know what hydrostatic pressure feels like. It’s not an unpleasant sensation, being enveloped by a few hundred cubic tonnes of water, insulated from the hubbub of everyday life. Scuba divers can comfortably descend to -30 metres without any noticeable effects of pressure, providing their inner ears have been equalised sufficiently. (A sharp blow of the nose while pinching the nostrils usually does the trick.) Here the ambient pressure is around four times greater than on the surface, and it is within this cobalt-coloured ocean realm that the great majority of recreational diving takes place.
Below 30 metres, things start to become a little more complex. The main factor affecting humans at depth is that the gases we breathe normally, namely oxygen and nitrogen, start to become toxic. Divers venturing beyond -30 metres may start to develop symptoms of nitrogen narcosis, a condition Jacques Cousteau called “rapture of the deep”. The effects are similar to alcohol intoxication and get progressively worse the deeper the diver ventures. After 90 metres there is a high risk of incapacitation, blindness, unconsciousness and even death.
To mitigate against the effects of increased pressure, technical and commercial divers who operate at depth breathe a carefully calibrated mixture of gases, which includes helium. Given that we aren’t designed to subsist below water, the human body can cope surprisingly well at depth, as long as we’re breathing the right mix of gases. Nuno Gomes, who in 2005 set a world record for the deepest-ever ocean scuba dive of -318 metres, has experienced first-hand the extreme forces that are at play beyond -100 metres. During his preparations for the record attempt, a member of Nuno’s underwater team was filming a practice dive. “The camera was protected by a large, custom-made, reinforced housing. We had just reached 110 metres when there was quite a bang! The entire thing imploded. Steel, glass and plastic are not as compressible as water and human tissue. The human body is mostly water except for the empty spaces — lungs, sinuses, eustachian tubes. As long as the spaces inside are kept at the same pressure as outside, all is good.”
Atmospheric pressure isn’t the only characteristic of the ocean affected by depth. Mark Ellyatt, who alongside Nuno Gomes is one of only a handful of humans who have dived below -300 metres, described the way the appearance of the ocean alters as depth increases’ “As you lose light, you also lose colour. As you descend, different colours of the spectrum are gradually filtered out by the water. The first to go are the reds, followed by the yellows, and finally you are left with a sort of purple haze before you reach complete monochromatic blackness. Then the head torch goes on and a beam of light illuminates millions of particulates hanging in the murky water.” Nuno knows well the feeling of sinking through the twilight before being engulfed by the black void: “At around -120 meters it becomes quite dark, not pitch black, but gloomy and light is almost completely gone. From here on you are on your own. At -180–200 meters, light disappears completely. Total darkness, like someone turned out the light in a room. The torch beam will cut through the featureless gloom for some way until it is absorbed by the darkness and fades away.”
As light fades, the temperature of the water drops too. Even in warmer waters like the Red Sea, where Nuno set his record, the temperature at the bottom was only 4°C, the same as a refrigerator.“Despite being protected by a drysuit, I was very cold all the way down and I didn’t begin to warm up again until about -30 meters from the surface.”
Sound too is dramatically altered by depth. Nuno describes the ocean’s unique acoustic quality: “When you are alone in the darkness, the sound of the bubbles being released by your regulator becomes almost melodic, like the gentle tinkling of a wind chime. They have a soothing musicality. The deeper you go, the characteristics of the sound change; it gets bent and warped by the water density and the pressure.” Being around 800 times denser than air, water is actually a much better conductor of sound and with the high pressure at 300 metres, deeper sounds resonate further. “The distant sounds of propellors and engines of passing ships high above can be heard surprisingly clearly,” added Mark.
It’s worth pausing to consider the magnitude of 318 metres depth. That is the equivalent of New York’s Chrysler Building, once the world’s tallest man-made structure. Imagine it inverted beneath the ocean and being at the tip of the spire. Nuno suspects that dimensionalising a dive like this would probably be overwhelming if you were about to attempt it. He claims to only ever think of depth in 50-metre increments, which he says is about as far as you can ever really see beneath the ocean anyway. Mark Ellyatt believes good psychological preparation is critical for deep diving: “Extreme depth can have very dramatic and unpredictable effects on humans. People behave in different ways; some have panic attacks and severe anxiety. I’ve seen confident and experienced divers curl up in a foetal position and freeze.”
Another difficulty humans have to contend with below 150 metres is High-Pressure Nervous Syndrome. Some symptoms of HPNS are tremors similar to hypothermia: shivering, involuntary muscular spasms and even total loss of control over limbs and hands. Hallucinations and vomiting are also common. Nuno experienced severe HPNS in the later stages of his 318 metre descent in the Red Sea.“It became difficult to coordinate my limbs — they wouldn’t do what I wanted them to do. I could not easily grip the guide rope; my hand and fingers simply would not obey the instruction my brain was sending to them. If I had lost connection with that rope, I would have simply continued to fall a further five and a half kilometres to the bottom. At -300 metres I began to experience terrible convulsions and my whole body started to spasm violently. Even at the deepest part of the dive, I still had complete clarity of thought and, given the severe muscular convulsions I was experiencing, I was concerned that if the regulator fell out of my mouth I may simply not be able to put it back in and would drown.”
Humans have been subjected to even greater pressures in simulated conditions onshore. Divers have successfully completed tests in hyperbaric chambers to -701m (71 atm of pressure). Aside from showing the inevitable symptoms of HPNS, all the volunteers survived. None showed any impending signs of shrinking to a third of their size, as a styrofoam cup would, or collapsing like an aluminium can. The engineering principle of a “crush depth” — the submerged depth at which, a submarine, for instance, is expected to collapse due to pressure — doesn’t really apply to the human body. Contrary to what science fiction and horror movies would have us believe, we would not dramatically implode once the human threshold was reached. The reality is more likely far less spectacular and that we would gradually shut down as a consequence of our individual organs and anatomical systems being unable to function.
Whether humans can tolerate pressures beyond -701 metres — say, -1,000 metres — remains the subject of speculation. Unsurprisingly, willing human test volunteers aren’t queuing up outside the hyperbaric chamber to find out. Therefore, to understand what being 1,000 metres beneath the ocean is like, we must use our imagination. Let’s go back to the upside-down Chrysler Building metaphor. This time, visualise the Chrysler Building with the Eiffel Tower stacked on top, and the Empire State building stacked on top of that. This is 1,000 metres, give or take. That far beneath the ocean’s surface, you are in total darkness and in what is known as the bathypelagic zone, or the ‘midnight zone’.
The only natural light in the midnight zone is bioluminescence, self-generated by the organisms that inhabit it — small flecks of coloured light, dotted around like fully charged Super-LumiNova on a watch dial. The fish that survive at this depth have an otherworldly appearance. With their oversized eyes, phosphorous antennae and protruding fangs, hidden away in the dark is probably the best place for them. More sizeable occupants of this part of the ocean include the sperm whale and the elusive giant squid, which at more than 40 feet in length has inspired centuries of folklore and myths. Life at -1,000 metres is sparse and sedentary. While fish in the upper layers of the ocean patrol constantly in search of food, at -1,000 metres they conserve energy and lie in wait for something edible to drift their way. Their sensory receptors have adapted to detect the slightest pressure change in the water. Based on the superb sonic conductivity at this depth, even a ticking watch movement would be quite audible for some distance.
Ollech & Wajs have a long history of imagining the possibilities beyond human limitations. When you consider that the average depth of the ocean is 3,800 metres, and 80 % of it remains unmapped and unexplored, at -1,000m we’re still only splashing around in the shallow end.