Ocean Warming Threatens Microbe That Makes Nearly a Third of Earth's Oxygen

Science Alert - Climate | September 22, 2025
By Russell McLendon

Earth wouldn't be the lively place it is without photosynthesis, which harnesses solar energy to fuel most of the planet's food webs.

A variety of plants, algae, and cyanobacteria provide this service, but few do it quite like Prochlorococcus, considered to be Earth's most abundant photosynthetic organism. Tiny even for cyanobacteria, this marine microbe wields outsized influence in its habitats and beyond, contributing nearly a third of the planet's oxygen production and forming a vital foundation to food webs.

According to a new study, though, Prochlorococcus and its many beneficiaries may be more vulnerable to rising ocean temperatures than previously thought.

A transmission electron microscope image of Prochlorococcus marinus with overlay green coloring. (Luke Thompson/Chisholm Lab, Nikki Watson/Whitehead Institute/MIT)