Deoxygenation

It is the expansion of oxygen minimum zones in the world’s oceans as a consequence of anthropogenic emissions of carbon dioxide.

It is one of the most pernicious, yet under-reported side-effects of human-induced climate change.

The loss of oxygen from the world’s ocean is increasingly threatening fish species and disrupting ecosystems.

Deoxygenation is starting to alter the balance of marine life, favouring low-oxygen tolerant species (e.g. microbes, jellyfish and some squid) at the expense of low-oxygen sensitive ones (many marine species, including most fish).

Some of the ocean’s most productive biomes – which support one-fifth of the world’s wild marine fish harvest – are formed by ocean currents carrying nutrient-rich but oxygen-poor water to coasts that line the eastern edges of the world’s ocean basins.

As naturally oxygen-poor systems, these areas are particularly vulnerable to even small changes in ocean oxygen.

Impacts here will ultimately ripple out and affect hundreds of millions of people.

Species groups such as tuna, marlin and sharks are particularly sensitive to low oxygen because of their large size and energy demands.

These species are starting to be driven into increasingly shallow surface layers of oxygen-rich water, making them more vulnerable to overfishing.

Very low ocean oxygen can also affect basic processes like the cycling of elements crucial for life on Earth, such as nitrogen and phosphorous.