That depends on whether you've got photosynthetic or abiotic algae. Blue-green algae produce oxygen.
One theory on ice-ages involves what's basically pond-lilly taking over the Arctic, which at the time was a shallow sea with a freshwater lens over salt water.
One theory on ice-ages involves what's basically pond-lilly taking over the Arctic, which at the time was a shallow sea with a freshwater lens over salt water.