Marine scientists call for global tracking of oxygen loss leading to dead zones | Ocean | Guardian

2021-11-22 08:51:11 By : Ms. Meryl Zhu

Scientists from six continents say that monitoring systems can help protect coral reefs and fisheries around the world

Last modified on Friday, November 19, 2021 14.01 EST

A team of marine scientists from six continents urgently called for the establishment of a global system to track the loss of oxygen in parts of the ocean and coastal waters that led to the death zone, where almost no organisms can survive.

Experts say that ocean heating, mainly caused by burning fossil fuels, is making the problem worse, with serious consequences for communities, fisheries and ecosystems around the world.

57 scientists from 45 institutions in 22 countries have put forward the urgent need for a global monitoring system, which they say can help protect ecosystems such as coral reefs and fisheries around the world.

In the so-called hypoxic event, the dead zone of hypoxia or anaerobic can last for several days to several months, leading to the death of fish, plants and crustaceans.

Coastal events are usually triggered by extra nutrients flowing into the estuary, and are made worse by the warming of the sea.

There are hundreds of hypoxic zones on coastlines around the world, and there is evidence that oxygen levels in parts of the high seas are also declining.

Professor Karin Limburg of the State University of New York is one of the scientists who called for the establishment of a global ocean oxygen monitoring system under the United Nations.

"There is an urgent need to record and predict hypoxic events and hypoxic hotspots in order to take protective actions for aquaculture, take preventive measures for affected fisheries, and monitor the health of important fish populations," Limburg said.

"Without this understanding, we would know nothing about the impact that has a huge economic and ecological impact."

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Professor Jodie Rummer of James Cook University is the co-author of an article published on Sunday in the journal Frontiers in Marine Science, which illustrates a case for monitoring systems.

"Everything needs oxygen in the water. Most life in the ocean is intolerant of hypoxia," Lamer said.

"These problems are getting worse because we have not solved the problem of nutrient loss and our waters continue to warm.

"We still don't know the long-term impact of these issues that affect the fisheries and aquaculture industries that feed humans."

Rummer is coordinating a new project with UNESCO to study the impact of low oxygen levels on sharks in the world.

She said that there is new evidence that corals in tropical regions are also at risk of hypoxic events.

There are already a series of equipment used to measure oxygen in the ocean, including underwater gliders, free-floating instruments and sensors.

But scientists say that more is needed, and the data has not been publicly available or standardized, which makes it more difficult to conduct global assessments and research when problems become urgent.

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The lead author of the article, Professor Marilaure Grégoire from the University of Liège in Belgium, said: "At present, the quality and availability of oxygen data in international databases cannot accurately estimate long-term oxygen decline."

One of the most famous hypoxic areas is the vast area that now forms in the Gulf of Mexico every summer, extending from the mouth of the Mississippi River. The largest dead zone was formed in 2017, covering an area of ​​23,000 square kilometers.

Adding nutrients to coastal waters will feed oxygen-consuming bacteria, causing levels to drop. But warm sea water also increases the metabolism rate of organisms, which means they need more oxygen to survive. Most importantly, as the water temperature increases, the amount of available oxygen decreases.

Australia has experienced many hypoxic events caused by nutrients and pollution from degraded soil, roads and farms that enter the estuary after heavy rains.

The extra nutrients will cause a surge of bacteria in the water, which will take away oxygen. In some cases, fresh water forms a layer on the surface to prevent water from mixing, creating a dead zone underneath.

Professor Perrancook of Monash University in Melbourne said that almost all organisms in the oceans, lakes and waterways need oxygen.

"It is temperature that controls oxygen," Cook said. He is not one of the authors of the paper, but said he strongly agrees that a global monitoring system is needed.

He said: "People are very worried that the oxygen in our waters is decreasing, which will have a negative impact on the health of fish and ecosystems.

"Just as we invest in climate change monitoring to help us understand what is happening, it is important to understand that water is changing due to human influence."

A study found that between 2007 and 2019, the temperature of the estuary waters of more than 1,100 kilometers of New South Wales coastline increased by more than 2 degrees Celsius.

He said that areas of northern New South Wales and southwestern Victoria, such as Lake Gippsland and the mouth of the Anglesey River, have experienced hypoxic events, but the reasons are not always the same. The Derwent Estuary area of ​​Tasmania also often suffers from hypoxia.

Dr. James Tweedley, an aquatic ecologist at Murdoch University in Perth, studied the effects of hypoxia on the estuary, including the three-month event that occurred at the Swan Canning estuary after the 2010 storm.

He said that the lack of oxygen in the estuary may have a serious chain reaction, because they are a hotbed for crabs and fish, and when the oxygen level drops, their larvae can hardly escape.

"We now have technology that can record what happens in the ocean," he said.

"Having [a global system] will be very valuable because it is the basis for climate change and global change modelling. We need to understand this on a global scale."