Deep-sea anoxia is not the only explanation for the δ34S excursion of pyrite. Carbonate-associated sulfate maintains high 32S levels, indicating that seawater in general did not experience 32S depletion during the glaciation. Even if pyrite burial did increase at that time, its chemical effects would have been far too slow to explain the rapid excursion or extinction pulse. Instead, cooling may lower the metabolism of warm-water aerobic bacteria, reducing decomposition of organic matter. Fresh organic matter would eventually sink down and supply nutrients to sulfate-reducing microbes living in the seabed. Sulfate-reducing microbes prioritize 32S during anaerobic respiration, leaving behind heavier isotopes. A bloom of sulfate-reducing microbes can quickly account for the δ34S excursion in marine sediments without a corresponding decrease in oxygen.