Tim · Tim Powell, a diving enthusiast, uploaded a video of his finger being bitten and bleeding from a small moray eel about 20 meters in the ocean.
At this time, his blood was neither bright red nor crimson, but green, like emerald.
Divers shed green blood. Source: YouTube
In fact, not only humans, but also fish that have been slandered in the deep sea have green blood. Sometimes, divers will use spearguns to catch fish underwater, and if they reach a certain depth, green blood will ooze from the wounds of the fish, but their blood will also be red when they are killed on the shore.
Source: YouTube
Source: YouTube
Of course, it doesn't necessarily need to be on shore, it's just that in shallow waters, the blood of the cut fish is also red.
Source: YouTube
It should be noted that the blood of most fish is red because their blood contains hemoglobin, which is rich in iron and is able to bind to oxygen, which transports it in the body. Hemoglobin appears red when combined with oxygen, which is why most animal blood, including human and fish, appears red on land.
Source: Internet
The color of blood, both on the ground and under deep-sea pressure, is basically determined by the state in hemoglobin where iron atoms bind to oxygen. The color of the blood varies mainly from bright red (oxygen-rich blood) to dark red (oxygen-deficient blood).
But we have to know that no matter what color it is, it is seen by the eyes. Physics lessons in middle school tell us that anything we see is because light is reflected into our eyes. Red blood appears red because it absorbs other light spectrums and reflects red light.
Source: Internet
In the deep ocean, the phenomenon of red blood appearing green is not due to the change in the color of the blood itself, but due to the specific light conditions under the water and the way humans perceive it.
There are several main factors involved: the light-absorbing properties of water, the mechanism by which the human eye perceives color, and the color reflection of blood.
Water is able to absorb different wavelengths of light, but this absorption has different effects on different wavelengths of light. In water, the absorption of light is mainly caused by the water itself and the substances dissolved in it, such as organic matter and minerals, as well as suspended particles.
After the sun's rays enter the water, the red light, due to its longer wavelength, has a lower energy and is more easily absorbed by molecules and other substances in the water and converted into heat energy instead of continuing to propagate forward. This means that below a certain depth, most of the red light is already absorbed by water, while short waves such as blue and green light can penetrate it.
Source: Internet
Human visual perception of color is achieved through cone cells on the retina in the eye, which are sensitive to different wavelengths of light. Under normal light, the human eye is able to perceive a wide range of colors. However, in a deep-sea environment where only blue light can reach, there is a lack of enough red light, which affects our normal perception of color, which is difficult to observe normally in the deep sea.
In addition to this, we also need to know the diffuse reflectance of human blood. Scientists have found that in natural light, human blood reflects not only red light (mostly), but also some green light, as shown in the figure below.
Diffuse reflectance of human blood, hematocrit of 33%, oxygen saturation of 100% Source: Christopher S. Baird
So, in the deep ocean, in the absence of a red light source, the blood looks green.
This is also why some smartwatches use green LEDs to monitor heart rate. Green light is more sensitive when it comes to detecting changes in blood flow. As green light passes through the skin and blood vessels, small changes in the amount of blood cause changes in the intensity of the reflected or transmitted light, making it possible to calculate the heart rate by analyzing these changes.
Source: Junkie
If in the deep sea, instead of relying on natural light, divers bring their own artificial lighting, such as a flashlight, to illuminate their injured hand, and find that their blood turns red again.
This is why most of the deep-sea animals are red. For example, the newly discovered single-spiny frogfish a while ago is a lovely red color.
图源：SCHMIDT OCEAN INSTITUTE
In the deep sea, red animals appear almost black or completely transparent in such an environment because red light is almost completely absorbed. This color makes them virtually invisible to predators, providing an effective means of camouflage. Red becomes very difficult to detect in the deep sea, allowing these creatures to better avoid the attention of predators.
(You can see the red color in the picture because of artificial light, and it is a different state in natural light)
Title: Kunio Amaoka
In addition, organisms in the deep-sea environment need to survive in extreme conditions, including low temperatures and high pressures. While red may have a limited direct effect on heat preservation or energy absorption, this color may be related to certain special biological compounds in their bodies that are used to absorb and utilize very small amounts of light energy in their surroundings.
If you see green blood in a game, it has nothing to do with science......
bibliography
[1]https://pubmed.ncbi.nlm.nih.gov/12819275/
[2]https://www.nationalgeographic.com/animals/article/walking-fish-deep-sea-new-species-chile
[3]https://opg.optica.org/as/abstract.cfm?uri=as-59-6-826
Planning and production
来源|把科学带回家(id:steamforkids)
Author: Su Chengyu