Loss of oxygen in ocean; A bad sign for marine life

Madrid: The loss of oxygen from the ocean due to climate change risks "dire effects" on sea life, fisheries and coastal communities, a global conservation body said Saturday. The International Union for the Conservation of Nature (IUCN) said that around 700 sites had been identified globally with low oxygen levels -- up from only 45 in the 1960s.

In the same period, the group warned, the volume of anoxic waters -- areas totally devoid of oxygen -- have quadrupled. The ocean absorbs around a quarter of all fossil fuel emissions, but as global energy demand continues to grow there are fears that the world's seas will eventually reach saturation point. Oceans are expected on current trends to lose 3.0-4.0 per cent of their oxygen globally by 2100.

However, most of that loss is predicted to be in the upper 1,000 metres, that is the richest part of the ocean for biodiversity. "With this report, the scale of damage climate change is wreaking upon the ocean comes into stark focus," said IUCN acting director Grethel Aguilar.

"As the warming ocean loses oxygen, the delicate balance of marine life is thrown into disarray." The largest peer-reviewed study to date on ocean oxygen loss concluded that deoxygenation is already altering the balance of marine life to the detriment of species that need more of the life-giving gas.

Species such as tuna, marlin and sharks -- many of which are already endangered -- are particularly sensitive to low oxygen levels due to their large size and energy demands. But loss of oxygen is affecting species across the food chain. The biomes that support around a fifth of the world's current fish catch are formed by ocean currents that bring oxygen-poor water in to coastlines. These areas are especially vulnerable to even tiny variations in oxygen levels.

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