A single deep dive leaves chemical fingerprints of stress
When 40 male divers made one open-water dive to 80 meters breathing helium-oxygen, their blood and saliva changed in ways that point to physical stress. The share of granulocytes, a type of white blood cell, rose, while lymphocytes, intermediate cells, red blood cells, hematocrit (the proportion of blood made up of red cells), and platelets all fell [2]. At the same time, creatine kinase and its heart-specific form CK-MB rose in serum, along with salivary amylase and testosterone, while salivary IgA, an antibody involved in immune defense, dropped [2]. The authors read this pattern as activation of the blood vessel lining, skeletal-muscle damage, oxidative stress, and a general stress response [2].
The dive itself was brief at depth: total diving time was 280 minutes, but breathing the helium-oxygen mix lasted only 20 minutes [2]. That short exposure was enough to move these markers, which suggests the body reacts quickly to the combination of depth, pressure, and breathing gas. It is worth keeping in mind that these are biomarker shifts measured around a single dive, not evidence of lasting harm.
Lungs tighten a little and the body sheds weight
A separate field study followed seven divers making sixteen deep dives to 90 and 120 meters over four days using closed-circuit rebreathers, which recycle the breathing gas. After surfacing, forced vital capacity, the maximum amount of air a person can forcefully exhale, was lower than before, at 84 percent of predicted values versus 91 percent [3]. The ratio of forced expiratory volume to forced vital capacity was higher, while other lung measures and blood oxygen saturation stayed unchanged [3].
Body mass also dropped, from a median of 73.5 kilograms before the dives to 70.0 kilograms after, without a change in hematocrit [3]. Heart rate variability increased after diving, and a measure of visual flicker perception was unchanged [3]. The authors describe the weight loss and reduced lung capacity as possibly imposing meaningful physiological stress on divers [3]. Because this was a small pilot study of repeated bounce dives, the size and durability of these changes are not established.
Depth is a different environment, not just more water
The deep ocean is described as fundamentally different from shallow seas, a space whose unique conditions call for approaches distinct from those used in shallower water [5]. That framing helps explain why diving to 80 or 120 meters is not simply a deeper version of a shallow dive: the body is working under high pressure and breathing gas mixtures of helium, nitrogen, and oxygen rather than ordinary air [2][3].
There is also a broader point about how people relate to the deep ocean. One analysis argues that the deepest layers have been treated with a sense of fearful otherness, and it approaches the ocean through human physiology and the body [1]. That is a cultural and conceptual observation rather than a measurement, but it fits the practical picture: the deep ocean is a place the unprotected human body cannot occupy, which is why the evidence about the body comes from technical divers and their biomarkers.
What these dives can and cannot tell us
The available studies look at short windows: samples taken before and after a dive, or across four days of repeated dives [2][3]. They do not tell us whether these changes persist, whether they accumulate over a diving career, or how they differ between people. The 80-meter study involved 40 male divers and the rebreather study only seven, so the findings describe those groups rather than the general population [2][3].
It is also important to separate what was measured from what it means. Rising CK-MB and falling IgA are consistent with muscle stress and immune change, but the studies report associations in biomarkers, not confirmed clinical outcomes [2]. The lung and weight changes after repeated dives are described as possibly stressful rather than proven harmful [3]. In short, the body clearly responds to deep diving, and the response is measurable within a single dive, but how much it matters over time remains an open question.
Sources used in this answer
Interspecies Diplomacy in Anthropocenic Waters: Performing an ocean-oriented ontology
The paper examines ocean-oriented ontology through human physiology and body-oriented perspectives, referencing the deepest ocean layers and framing them with a sense of fearful otherness.
Human Physiological Responses to a Single Deep Helium-Oxygen Diving
A single 80-meter helium-oxygen dive in 40 male divers shifted blood cell proportions and raised markers of muscle damage, endothelial activation, oxidative stress, and physiological stress.
Physiological effects of mixed-gas deep sea dives using a closed-circuit rebreather: a field pilot study.
Repeated 90-120 meter mixed-gas rebreather dives in seven divers were followed by lower forced vital capacity, reduced body mass, and increased heart rate variability.
Deep Textured 3D Reconstruction of Human Bodies
The paper presents a deep learning method for textured 3D reconstruction of human body shapes from a single RGB image, with no connection to ocean environments.
Deep differences: expanding the marine social sciences and humanities into the deep ocean
The paper argues that the deep ocean is fundamentally different from shallow seas and warrants distinct social science and humanities research perspectives.