The ocean, rather than rainforests alone, plays a major role in producing the oxygen generated on Earth each year, with microscopic phytoplankton responsible for roughly half of global photosynthetic oxygen production.
Phytoplankton, including tiny algae and photosynthetic bacteria, live in the sunlit upper layers of oceans. Despite being mostly invisible to the naked eye, these organisms use sunlight and carbon dioxide to produce organic matter and release oxygen through photosynthesis.
Scientists estimate that marine and land ecosystems contribute broadly similar amounts to Earth’s total annual oxygen production, although the exact share varies depending on observations, time periods and scientific models.
Researchers caution that this does not mean the ocean adds half of the oxygen currently stored in the atmosphere every year. Much of the oxygen produced by phytoplankton is later consumed by marine organisms and decomposition processes.
Phytoplankton also form the foundation of marine food webs and play a major role in the global carbon cycle. Satellite observations help scientists monitor plankton by measuring changes in ocean colour caused by their pigments.
The findings highlight the importance of protecting marine ecosystems, as microscopic life in the oceans remains essential to global biodiversity, climate processes and Earth’s oxygen cycle.