'Dead Zone' threat to fisheries in the Indian Ocean

A mysterious dead zone - 60,000 sq km virtually devoid of oxygen and life - has been discovered in Australia's northeast. Photo / Getty Images

A huge, mysterious 'dead zone' - 60,000 sq km devoid of oxygen and life - has been discovered in the Indian Ocean to the west of Australia.

Such zones have already been found off the coasts of North and South America, western Africa and the Arabian Sea.

But this is the first time one has been found encroaching into South-East Asia.

A study published in the science journal Nature Geoscience reveals a new 'dead zone' appears to be emerging in the Bay of Bengal, in waters extending from 100m to 400m in depth.

Dead zones are normally associated with a lack of oxygen and concentrations of microbes stripping the vital nutrient nitrogen out of the water.

In the case of the Bay of Bengal, no such nitrogen loss has yet been detected.

And traces of oxygen have been found - at levels 10,000 times lower than normal air-saturated surface waters.

While this is less than is needed to support most life, it also impedes nitrogen-harvesting microbes.

"We have this crazy situation in the Bay of Bengal where the microbes are poised and ready to remove lots more nitrogen than they do, but the trace amounts of oxygen keep them from doing so," lead author of the study Dr Laura Bristow of the Max Planck Institute says.

Once the last traces of oxygen evaporate, the Bay of Bengal could become 'a major global player' in taking nitrogen out of our oceans.

This could have a severe impact on marine nutrient balances, and therefore the density of marine life.

It is feared increasing levels of fertiliser feeding into the Bay of Bengal from high intensity population centres will result in the last of this oxygen being absorbed.

"Time will tell, but the Bay of Bengal is at a 'tipping point', and we currently need models to illuminate how human activities will impact the nitrogen cycle in the Bay of Bengal, and also globally," Dr Bristow says.