The short answer is very simple . Initially, the body will likely sink to the bottom quickly, but as the body decomposes and gases are released into the body, the corpse will return to the surface as a result of buoyancy.
The density of the human body is similar to the density of water, and what keeps us floating is basically the air in our lungs. Hence a corpse begins to sink as the air in its lungs is replaced by water. Once there is no air left in the lungs, the body will end up on the bottom. But … when any organism dies, it goes through the putrefaction phase: a series of chemical, physical and biological changes that end up returning the body to the food chain.
Why do dead bodies seem to float naturally?
Thus, at this time, the bacteria that normally live in the digestive system continue to feed on proteins and sugar in the soft tissues of the body, and excrete gases such as carbon dioxide, ammonia, hydrogen and methane. As these gases accumulate in the body cavities, the corpse will begin to rise to the surface of the water.
It is clear, therefore, that if we see a body floating in the water, it does not mean that it has immediately drowned. In fact, if a person drowns, it will probably take longer for the body to return to the surface.
The air in our lungs acts as a buoyant force for the body, making it impossible for you to lie on the bottom of a pool. However, in the case of a dead body, they have no control over whether their lungs fill up or not. If the corpse falls face down into the water, it may never sink to the bottom, as there will be no real chance of air escaping from the lungs. However, if the corpse is on its back, air can escape, water can take its place, and the body can quickly sink.
Death by drowning
If a person drowns, they do not necessarily die because the water has filled their lungs; but, on the contrary, the usual thing is that the person suffocates because the windpipe closes in the presence of water. In this case, a body could potentially float for longer periods before sinking hopelessly to the bottom.
Back from the depths
Let’s go back to the bacteria in our body. We have already seen that just because the body dies does not mean that bacteria within the body do too. They only need one food source to live, and they can even function anaerobically in the absence of oxygen . So as bacteria consume our intestines and so on, they release gas and since this gas has nowhere to go, it will start to fill up other parts of the body.
As the body slowly begins to swell and rot, that newly formed gas develops the same penchant for buoyancy as oxygen, lifting the corpse to the surface. The corpse can break due to the pressure of the air inside; at this point, the body could sink a second time, although the process of decomposition and putrefaction would continue, filling the body with gas and sending it back to the surface.
While it is true that the volume of the body will increase notably, the weight of the corpse will not , which will facilitate the floating of the body. Given the possible caveats, a corpse could return to the surface in a few hours, days, or even weeks.
One last curiosity: the decomposition process is particularly slow at extremely cold temperatures, so it could take a long time for a body to reappear on the surface.
