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The BBC News article Pink lake in Australia attracts and delights tourists describes an artificial salt lake in Westgate Park, Melbourne, Australia that tuns pink around February and then in "late Autumn, until cooler temperatures restore it back to blue."

I am not sure about the autumn part as it's in the southern hemisphere, but my question is about the color change.

  • Could they mean beta carotene rather than beto carotene?
  • And if so, does the pigment stay inside the algae or is it released into the water to produce this color change?
  • And why pink, rather than the orange color we associate with carrots?

enter image description here

In those conditions, the lake's algae produces a red pigment called beto carotene

enter image description here

The lake's pink colour typically lasts through to late Autumn, until cooler temperatures restore it back to blue.

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The "beto" is a typing mistake. Beta is an organic chemistry label referring to a beta-ring of 6 carbons that exists at either end of a carotenoid polymer C40-Hx.

It is localized in the chloroplast. The plants don't really have a mechanism to release pigments, they can re-metabolize chlorophyll. The volvocalean algea Dunaliella salina is used to harvest beta-carotene in Karratha, Western Australia, from salt lakes. The can have 12% beta-carotene as dry-matter content, the highest of any known source. The squares are probably salt. enter image description here the algea afterwards: enter image description here

There are over 1,100 known carotenoids of which at least 700 have been identified in plants. They include carotene and xanthophylls, and carotene include beta-carotene. The plants and algea use it to protect themselves from intense sunlight and UV's. It is an anti-oxidant. enter image description here

Pink doesn't actually exist as a color. It is imagined when green and blue light is sensed by the eye, while red is at a maximum. In the lakes, we know there is 80% red and 20% green pigment in the algea. All that is required would be 20% blue to percieve pink. I don't know where the blue color comes from, the sky/water. Orange is complex for the eye, and so is pink, because we can only see red green and blue. enter image description here enter image description here

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  • $\begingroup$ Oh, this is a thoroughly wonderful and wonderfully thorough answer, thank you! $\endgroup$ – uhoh May 19 '19 at 8:12
  • $\begingroup$ Hey thanks! People should be warned that the BBC takes 150 dollars per year in taxes from the 51st state and is keener on hiding state secrets than journalism, it's the same as RT in higher secrecy. $\endgroup$ – com.prehensible May 19 '19 at 8:31
  • $\begingroup$ oh-kay.... I've been duly warned ;-) $\endgroup$ – uhoh May 19 '19 at 8:35
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Not sure which kind of microorganism they talk about, but beta-carotene is a red-orange~ish pigment (as you pointed out, also produced by carrots). The pink coloration I would assume is the product of the color mixture of the pigment with green-blue from the water (not the water itself but the blue reflection from the sky + any other algae in the water). If they release it (the beta-carotene) to the water, again not sure which organism they talk about but it's probably not like it, since beta-carotene is a photosynthetic compound. Therefore is pretty likely they may want to keep it inside.

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  • $\begingroup$ Do you have any sources? $\endgroup$ – TanMath Apr 1 '19 at 3:01
  • $\begingroup$ It was pure guess, but here you go $\endgroup$ – user50823 Apr 1 '19 at 8:54
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    $\begingroup$ @N.P. the message "...requires additional references. Please edit to add citations to reliable sources..." should be interpreted literally. If you can edit your post to add your citation to your answer, along with a short description of how the reference supports your answer (usually a short block quote from it is sufficient) that would improve the quality of your answer. Thanks! $\endgroup$ – uhoh Apr 2 '19 at 23:41

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