[DylanBohlender]

I think the premise here is that there is some sort of physical limitation that causes cyanobacteria to have a maximum "carrying capacity" of oxygen, and stretching timecycles causes that threshold to be exceeded, leading to oxygen leaks.

Analogously, think of memory management in a computing context. You have a program running that gradually allocates memory linearly over a certain time period (daytime), but then releases all that memory linearly during another time period (nighttime). Say you're dealing with 4GB of memory and you run the memory-increasing part for 6 hours, then run the memory-decreasing part for the next 6 hours, and so on. Suppose you never allocate the full available 4GB when you're dealing with a 6 hour on/off timecycle (the rate of memory allocation is too low to get to 4GB in 6 hours) - but what happens if you extend the timecycle? There's some timecycle length at which you will finally attempt to allocate more memory than the 4GB your hardware is capable of, so the host OS starts swapping or writing stuff to disk to deal with the excess.

Biological systems don't have a "host OS" that regulates their molecular byproduct management though. Extra atoms/molecules are just going to escape into the surrounding environment. Perhaps the oxygen buildup during the daytime might have worked this way with the cyanobacteria - longer days led to more oxygen being produced than could be physically retained in the immediate vicinity of the cyanobacteria (some type of saturation effect), so all the oxygen in excess of the saturation threshold effectively "escaped" and became unavailable for metabolic "re-consumption" at nighttime. Thinking about the longer nights that accompany the longer days, there's probably a period of time in these longer nights during which all the "nearby" oxygen has been fully consumed, and the cyanobacteria more or less sit idle.

Oxygen saturation in the surrounding environment seems like the missing logical piece from this popsci article.

[ncmncm]

I think the key is that chemical reaction rates vary exponentially with temperature. As temperature increases, reaction rates increase up to hard resource limits. But there is no limit on how slow reaction rates may get as temperature falls, and a slow-enough rate is effectively zero. Thus, an increasing fraction of the night has, effectively, no activity at all.