Two developments showing action must be taken over the planet’s oceans

Oceans suffocating as huge dead zones quadruple since 1950, scientists warn

Areas starved of oxygen in open ocean and by coasts have soared in recent decades, risking dire consequences for marine life and humanity

A fisherman on a beach blanketed with dead sardines in Temuco, Chile. In coastal regions, pollution can cause algal blooms and when the algae decompose oxygen is sucked out of the water.
 A fisherman on a beach in Temuco, Chile that is blanketed with dead sardines, a result of algal blooms that suck oxygen out of the water. Photograph: Felix Marquez/AP

Climate change caused by fossil fuel burning is the cause of the large-scale deoxygenation, as warmer waters hold less oxygen. The coastal dead zones result from fertiliser and sewage running off the land and into the seas.

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Coral reefs head for ‘knock-out punch’

Surveys of the bleached/dead corals at Zenith Reef, GBRImage copyright – ANDREAS DIETZEL
Image caption – A diver surveys bleached/dead corals on Zenith Reef, part of the Great Barrier Reef

Repeat bouts of warmer seawater are posing a significant challenge to the world’s tropical corals. A study of 100 reefs, published in Science Magazine, shows the interval between bleaching events in recent decades has shortened dramatically. It has gone from once every 25-30 years in the early 1980s to an average of just once every six years today. Bleaching is caused by anomalously warm water, which prompts coral polyps to eject their symbiotic algae.

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