The microorganisms of Grand Prismatic Spring

Grand Prismatic Spring in Yellowstone is located in the Midway Geyser Basin and is teeming with the microbial life of thermophilic bacteria. These photosynthetically active microorganisms produce the vivid colors of this up to 70° hot spring. The color zonation marks the different inhabitants of the different temperature ranges around the hot spring. In addition, algae and protozoa thrive in the outer areas of the spring at lower temperatures.
These microorganisms form mats by secreting a sticky organic substance that holds the cells together. The main pigment of photosynthesis is green chlorophyll. Masked with carotenes, it causes yellow, orange and red colorations. This coloration increases significantly in summer, as carotenes protect the cells of microorganisms from excessive UV exposure of the sunlight. In winter, therefore, a greener color predominates.
The color sequence also indicates the temperature zoning of the hot spring. Microorganisms thrive best at 45-60°C (113-140°F) and therefore prefer to settle at the outer periphery. The blue water in the center of the spring is too hot for living organisms and therefore shows the shortwave blue that is not absorbed in the color spectrum of light.
In the transition area to deeper water, which better protects the bacteria from the ultraviolet radiation of the sun, the green tones of chlorophyll are increasingly prevalent. The sharply defined yellow transition area marks the boundary between the chlorophyll and carotene-occupied bacterial mats.
In contrast to the geysers which erupt at regular or irregular intervals, hot springs show a rather calm and steady flow of boiling water. This is due to the lack of constriction in the underground conduit system. Therefore the boiling water can slowly cool down on its way to the surface. This makes it slightly denser and sinks back into the depths, continuously replaced by rising hot water. This process causes the continuous vertical circulation of water.