Deep Blue: Why we love the sea

IOL News

16-07-2025

Veruska de Vita is the author of Deep Blue: Why we love the sea.
Image: Supplied.
Veruska de Vita has sea water in her veins.
Last week the Johannesburg-based author released her ode to the ocean; Deep Blue: Why we love the sea.
Both a freediver and open water swimmer, de Vita has felt the call of the ocean throughout her life. By melding science, storytelling, and her own free-diving adventures she explores the impact it has on all emotional and physical wellbeing. Below is an extract from the book which retails for R330 and can be found at all good book shops.
Deep Blue is an ode to the ocean and all the benefits it provides. The 256 page book is an invitation to dive in and understand why the ocean calls to us.
Image: Supplied.
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Deep Blue: Why we love the sea.
Humans have been diving to great depths on a single breath for millennia. Staggering distances have been recorded since the early 1900s, with Giorgos Statti in Greece diving to 70 metres to retrieve a coin, Frenchman Jacques Mayol plunging to 100 metres in 1976 and Austrian Herbert Nitsch reaching 214 metres in 2007 using a weighted sled to descend and a buoyancy device to surface. More recently, William Trubridge dived to 102 metres in 2016, Alessia Zecchini reached 123 metres in 2023 and Alexey Molchanov reached 133 metres in the same year – all using a monofin. A monofin is a fi n that both feet fit into, giving the diver a dolphin-like 'tail'.
Professional freedivers continue to extend the limits of their reach, going a few or many metres deeper at each world record attempt. The sport has limitations set by the human body's response to lack of oxygen, increased carbon dioxide and mounting water pressure.
I like to think that the abilities of competitive freedivers point to the fact that humans are semi-aquatic. Our bodies seem built for water immersion, some bodies being more adept than others. Most babies, when put into water, instinctively react by swimming and holding their breath. This reflex has been attributed to the cause of sudden infant death syndrome (SIDS) or cot death, when babies stop breathing.
Beth Neale, a South African competitive freediver you'll read about later, submerged her daughter Neve when she was three months old. Beth tells me that Neve held her breath, exhaled a little, but it was obvious that her mammalian diving reflex had kicked in. 'She is so comfortable in the water that, as a baby, when I went into the ocean, as the water went above my knees and touched her feet, she put her face in the crook of my neck and fell asleep,' says Beth.
From all that Beth has researched about diving reflex in children, what she understood about her own toddler is that the reflex becomes a lesser response beyond the age of six or seven months. Babies experience a laryngospasm, which is when the throat naturally locks, and before six months this happens instinctively. 'With Neve it was still natural until about seven months. At eight months she would come up and cough a little, so I started teaching her,' says Beth. Beth also explains that when the face is immersed in water, chemoreceptors around the eyes push the diving reflex to kick in sooner, which is why during her record attempts she prefers to go without a mask.
Some believe that the diving response stops when a toddler begins to walk, because the need to survive in water diminishes. Yet this reflex is inherent; we can access it and train ourselves to extend our time underwater, to harvest the treasures of the sea and enjoy the feeling of weightlessness. We continue to be seduced by water, whether we're diving, swimming, immersing ourselves in it for our health, simply playing in it as children or exploring its depths and its shallows. We heed its call to explore, find bliss and push our own physical and mental limits.
What happens to the human body during freediving? As the face is immersed in water, the mammalian diving reflex kicks in, slowing down the heart rate and causing blood to move to the thoracic area. This blood shift keeps the vital organs safe and provides protection for the lungs, so that they don't collapse. Unlike other diving mammals, humans have not adapted to managing lung compression – as a freediver swims deeper, the lungs become smaller.
The deeper the freediver descends, the smaller the volume of air in the body. At the water's surface, the atmospheric pressure is 1 bar. At 10 metres, it is 2 bars, halving the volume of air in the body. An interesting thing happens at about 20 metres: neutral buoyancy is reached, which means that one neither sinks nor floats. The freediver is simply suspended. Just beyond this point of equilibrium, hydrostatic pressure takes hold; one becomes negatively buoyant and is pulled downwards, entering a state of continuous freefall. This is what may have happened to freediver Natalia Molchanova – she may have reached this freefall depth and passed out, or she may have become disorientated, not knowing up from down, continuing to soar or drop to the greatest depths of the sea. A poetic ending for someone so in love with the water.
At 50 metres, a freediver continues to freefall and the lungs become more compressed. The lungs are at residual volume – the volume of air that remains in the lungs after maximum exhalation. The lung tissue is under strain and the freediver needs to be careful not to make big movements that could cause injury to any part of the pulmonary system.
At 100 metres, lung volume can decrease to between 9 and 4,5 per cent of surface volume – the lungs become the size of pillboxes. Yet some individuals are extremely tolerant of lung compression at depths beyond this.
Chris McKnight is a research fellow in the School of Biology at the University of St Andrews in Scotland. His primary focus is marine mammals and he spends weeks, sometimes months, tracking and observing seals. This has led him to study some of the world's greatest vertical freedivers. He tells me that the elite freedivers were phenomenal to work with, very keen to have instruments attached to them on their dives. For him, it's fascinating – groundbreaking, even – to learn more about what happens inside the human body when submerged.
Chris and his team develop tools to follow diving mammals, measuring their heart rate and blood oxygenation, and changes in blood volume and brain oxygenation. 'Doing research on humans is a great stepping stone for us because we can ask questions to deeper understand what happens to the body during a dive.' Chris's Irish accent is thick. He chats to me from his home in Dublin – in the frame of the Zoom call, it looks like a surfer's house: lots of light wood, and everything in it is functional, not just decorative.
He explains that one of the crucial differences between humans and marine mammals is that we have sinuses and they don't. Without air-filled sinuses, marine mammals do not suffer the effects of changing pressure as much as humans do. We need to equalise to match the pressure in the middle ear to that of the depth. Another fundamental difference is that marine mammals don't have involuntary breathing movements, or contractions, and we do. Those who have held their breath to the point of these contractions know that they are uncomfortable and uncontrollable, and only stop once you exhale the carbon dioxide that has built up in the lungs.
'What freedivers who go to depths of sixty, a hundred metres have conditioned themselves to tolerate is phenomenal. They present an incredibly unique model for research,' says Chris. The research hopes to uncover how freedivers condition themselves to endure bouts of exceptionally low oxygen, which could help doctors treating cardiac patients.
'A few of the key things we found was a reduction in heart rate. The freediver's heart rate declined through the descent, just like a dolphin's, until it was 11 beats per minute at the bottom of the dive. In some of the deep dives that went past ninety metres, the heart rate got lower than what we'd expect to see in marine mammals, which was a surprise. Physiologically, deep diving is a stressful situation and I didn't expect heart rate to get as low as that.
'Other interesting changes occurred in oxygen levels. We measured the oxygenation of blood being delivered to vital organs like the brain. At the onset of exercise during descent, these levels, which are normally at 98 per cent, dropped enormously to as low as 25 per cent, which is well below the point at which we expect people to lose consciousness, which is at 50 per cent. One particular diver was tolerating levels in deoxygenation in the brain that far exceed those of marine mammals.
'Brain metabolic rate also drops, so it shuts down. A lot of the body is shut down so that it can better utilise oxygen for the major organs. It goes back to normal in 45 seconds once they surface and concomitant with that is brain oxygenation.
'We also saw a big increase in blood pressure and high intracranial pressure. Deep diving is a complete physiological assault,' says Chris.
What Chris observed, but did not document, while researching elite freedivers was their desire to push the boundary of where their body could go, how much pressure they could withstand and how much further they could fly into the depths, using only the oxygen they took into their lungs at the surface.
While the long-term effects of freediving on the mind and body have not been clearly established, some athletes feel a change in their mood. Chris tells me that after a number of days of doing deep dives, some of the divers had to take a day off because they felt cranky, angry and emotionally vulnerable. As freedivers immerse themselves deeper into the blue and as research on them continues, it will be interesting to see what is uncovered.
As I move my focus to those who enjoy the sea on the surface, I find a study done by the French Swimming Federation, published in 2024, on the physiological traits of extreme open-water swimmers. It piques my interest as I have wondered how regular and long hours of swimming affect the body. Surfers, and people who swim in cold water, can develop bony growths in the ear canal, or external auditory exostoses, a condition better known as surfer's ear. Swimming influences the lungs by increasing capacity, which is beneficial, but it can also make them swell from a build-up of fluids, which can cause illness. I've heard of long-distance swimmers falling ill with swimming-induced pulmonary oedema (SIPE), which affects those who swim in cold water under high physical exertion.
The French Swimming Federation study showed that the success of open-water swimmers depends on their ability to swim hard and fast for many hours. The researchers found a number of common attributes in 14 elite male open-water swimmers: a highly developed aerobic capacity, which is the body's ability to use oxygen efficiently during prolonged exercise, and elevated lactate thresholds, which allows them to swim longer and faster without muscle fatigue. The conclusion was this: the better a swimmer's body is at using oxygen and managing lactate build-up, the better they can swim.