Thanks for the image of the darkening, Hort.
Could be fungi blooming. I'm sure most of us are aware of cases where we left a cup with a small amount of water out on our desk for awhile to find after several days a small colony of black fungi growing.
Species of fungi can be remarkably resilient surviving subfreezing temperatures and high radiation environments:
Brine organisms and the question of habitat-specific adaptation.
Origins of Life and Evolution of Biospheres.
Volume 14, Numbers 1-4 / December, 1984
"Abstract Among the well-known ultrasaline terrestrial habitats, the Dead Sea in the Jordan Rift Valley and Don Juan Pond in the Upper Wright Valley represent two of the most extreme. The former is a saturated sodium chloride-magnesium sulfate brine in a hot desert, the latter a saturated calcium chloride brine in an Antarctic desert. Both
Dead Sea and Don Juan water bodies themselves are limited in microflora, but the saline Don Juan algal mat and muds contain abundant nutrients and a rich and varied microbiota, including Oscillatoria,Gleocapsa,Chlorella, diatoms,Penicillium and bacteria.
In such environments, the existence of an array of specific adaptations is a common, and highly reasonable, presumption, at least
with respect to habitat-obligate forms. Nevertheless, many years of ongoing study in our laboratory have demonstrated that lichens
(e.g.Cladonia), algae (e.g.Nostoc) and fungi (e.g.Penicillium, Aspergillus) from the humid tropics can sustain metabolism down to
-40°C and growth down to -10°C in simulated Dead Sea or Don Juan (or similar) media without benefit of selection or gradual acclimation.
Non-selection is suggested in fungi by higher growth rates from vegetative inocula than spores. The importance of nutrient parameters was also evident in responses to potassium and reduced nitrogen compounds.
In view of the saline performance of tropical Nostoc, and its presence in the Antarctic dry valley soils, its complete absence in our Don Juan mat samples was and remains a puzzle.
We suggest that adaptive capability is already resident in many terrestrial life forms not currently in extreme habitats, a possible reflection of evolutionary selection for wide spectrum environmental adaptability."
Issue 21 of Cosmos, June 2008
by Lauren Monaghan
Deep in the radioactive bowels of the smashed Chernobyl reactor, a strange new lifeform is blooming.
""Our findings suggest that [the fungi] can capture the energy from radiation and transform it into other forms of energy that can be used for growth," said microbiologist Arturo Casadevall from the Albert Einstein College of Medicine at Yeshiva University in New York, USA.
"Fungi are weird, yes. They chow down on everything from decaying plant matter to the more exotic fare of asbestos and jet fuel. But being able to produce their own energy, independent of an actual food source, and use dangerous ionising radiation to boot? That's very new and very exciting, Casadevall says.
"In 1999, a robot sent to map the inside of the reactor returned with samples of a particularly black fungi, indicating an abundance of the biological pigment melanin, which also colours your skin."
Fungi typically have large cell sizes. I'd like to see a MECA microscope image of the black stuff.