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Roughly half of the oxygen produced on Earth comes from the ocean, most of it made by phytoplankton, microscopic drifting organisms that photosynthesise like plants.

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Phytoplankton are mostly single-celled algae and bacteria living in the sunlit top layer of the sea. Like land plants, they use sunlight to turn carbon dioxide and water into sugar, releasing oxygen. Estimates of their share of the planet's oxygen production range from about 50% to 80%, because it is hard to measure. One tiny bacterium alone, Prochlorococcus, may produce up to a fifth of it. Most of the oxygen made in the sea, though, is used up again by marine animals and microbes and by the decay of dead matter, so the ocean's net contribution to the air we breathe is much smaller than the headline figure suggests.

Türkçe oku
Dünya'da üretilen oksijenin kabaca yarısı okyanuslardan gelir. Bunun çoğunu, suda sürüklenen ve bitkiler gibi fotosentez yapan mikroskobik canlılar, yani fitoplanktonlar üretir.

Fitoplanktonlar, denizin güneş alan üst tabakasında yaşayan, çoğu tek hücreli alg ve bakterilerdir. Kara bitkileri gibi güneş ışığıyla karbondioksit ve suyu şekere çevirir, bu sırada oksijen açığa çıkarırlar. Gezegendeki oksijen üretiminin ne kadarını sağladıkları kolay ölçülemediği için tahminler yüzde 50 ile 80 arasında değişir. Prochlorococcus adlı minicik bir bakteri tek başına bu üretimin beşte birine kadarını karşılıyor olabilir. Yine de denizde üretilen oksijenin büyük bölümü deniz hayvanları ve mikroplar tarafından, bir de ölü maddelerin çürümesiyle yeniden tüketilir; bu yüzden okyanusun soluduğumuz havaya net katkısı, bu rakamların düşündürdüğünden çok daha küçüktür.

Sources and further reading

Background reading: Phytoplankton
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