Extremities:  Geology and Life in Yellowstone and Implications for Other Worlds

OCTOPUS SPRING - 2 - Cool Water

As water flows away from the pool and cools down, the microbial mat communities change. The pink colonies of bacteria give way at ~60C to more familiar green of mats dominated by cyanobacteria (blue-green algae). At lower temperatures, eukaryotic algae (green, brown, etc.) come to dominate.

Octopus Spring photo 5


Octopus Spring photo 6
Below the pool ~ 5 meters, reddish and greenish microbial mats grow in slow-moving, cooler water outside the main channel. Here, T ~60C, pH = 8. The mats include a cyanobacterium (Synechococcus) that does oxygenic photosynthesis, and a green non-sulfur bacterium (Chloroflexus) that does anoxygenic photosynthesis.


Ten to fifteen meters farther down the flow, water temperature is barely above air temperature and pH remains slightly alkaline. The microbial mats are probably filamentous cyanobacteria ("blue-green algae"), mostly Phormidium and Calothrix.






In still water ~20 meters downstream from the spring, blue-green algae (cyanobacteria) forms cylinders and mushroom shapes instead of flat mats. These algal blobs resemble stromatolites, fossilized algal mounds that are found in rocks as old as early Archaean (>3 billion years old). [See "Stromatolites" for a closeup image.]


The microbial mats are commonly layered, with different communities at different depths. The vertical layering usually comes about because different microbes have different requirements for light and chemistry. For instance, a lower microbial community might be shielded from intense sunlight by the upper community. Here, a brown community lies on top of a green community.

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Copyright Allan Treiman, LPI.
Updated 11/15/02.
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