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Photo: ytb_prtscPhoto: ytb_prtscAfter we recently wrote about concerning decline of population of insects and the collapse ecosystem is faced with, scientists have warned about another part of the ecosystem that is stumbling under the burden of human influence. They counted 500 dead zones in the world’s oceans, and the level of oxygen in general in the oceans has declined 2%. "There are also many places around the Mediterranean, including the Adriatic, that have had problems with oxygen decline as a result of high nutrient inputs from agriculture, sewage and burning of fossil fuels", said Denise Breitburg, lead author of the new research published in Science.

After we recently wrote about concerning decline of population of insects and the collapse ecosystem is faced with, scientists have warned about another part of the ecosystem that is stumbling under the burden of human influence. Parts of the oceans have died, and other parts are barely breathing.As in Croatia we are often showing too little interest in global issues, although there is no doubt we are also a part of the planetary community of living beings, it is important to add that researchers have also found many areas with declining levels of oxygen in the Mediterranean and Adriatic sea

More and more areas of the world's oceans are losing oxygen and turning into dead zones where nothing can survive, the team of scientists led by Denise Breitburg from Smithsonian Environmental Research Center (SERC) from USA warned in the article published in Science Magazine on January 5th. 

Oxygen concentrations in both the open ocean and coastal waters have been declining since at least the middle of the 20th century. That is one of the most important changes that is happening in the world’s oceans caused by human activities. Apart from pollution, the most important driver of this phenomena is climate change, ocean warming that is caused by the increase of CO2 levels, the scientists have stated.

The increase of temperature decreases oxygen solubility in water, increasing the rate of oxygen consumption via respiration. As it was described in Science, oxygen declines in coastal systems are caused by increased loadings of nitrogen, phosphorus and organic matter coming from agriculture, sewage and the combustion of fossil fuels.

All this led to the fact that today, scientists have counted 500 dead zones in the world’s oceans, compared to less than 50 before 1950. Those zones cover the area the size of the European Union today, and the level of oxygenOxygen is fundamental to life in the oceans and we should be discussing declining ocean oxygen along with warming and acidification when we think about the effects of greenhouse gas emissions on the oceans and coastal waters in general in the oceans has declined 2%.

How is ocean deoxygenation going to impact life on the mainland and human lives is still a big unknown even to the scientific world, but is causing a major concern.

"We know of many local examples of negative effects on fish and shellfish that are important to economies and food security, but do not yet have the ability to project effects on the global scale. The same is true for effects on chemical cycles. N2O, a potent greenhouse gas, is produced under extremely low oxygen concentrations. As these low oxygen zones expand, more N2O is produced. But we don’t know for sure how much is released back into the atmosphere where it could worsen global warming", Breitburg said to H-Alter.

Low and declining oxygen levels in the open oceans and coastal waters, map by Science Magazine Low and declining oxygen levels in the open oceans and coastal waters, map by Science Magazine

But, as it happens in the ecosystems, the lack of oxygen is not the only problem oceans are faced with thanks to humans. Ocean acidification, increased levels of CO2, has been identified as one of the key planetary boundaries, which lead the Earth to the great unknown if crossed. Ocean acidification and deoxygenation are two phenomena linked in two ways.Oxygen concentrations in both the open ocean and coastal waters have been declining since at least the middle of the 20th century. That is one of the most important changes that is happening in the world’s oceans caused by human activities

"CO2 causes global warming, which worsens deoxygenation and also dissolves into the oceans and coastal waters to cause acidification. In addition, aerobic respiration, which uses up oxygen and releases CO2, is a major mechanism that reduces oxygen in the oceans and coastal waters. To make matters worse, increasing temperatures generally increase respiration rates, and therefore increase both deoxygenation and acidification", explained Breitburg.

Oxygen is fundamental to life in the oceans and we should be discussing declining ocean oxygen along with warming and acidification when we think about the effects of greenhouse gas emissions on the oceans and coastal waters, the team of scientists wanted to warn with the findings published in Science. If we don't act soon, in the extreme scenario, there is a possibility of a great extinction of species, and biodiversity decline is another planetary boundary that is already in the zone of high insecurity.

"The extinction trajectory is really an extreme possibility. It is very unlikely, but was presented to illustrate what could happen if greenhouse gas emissions continued to accelerate. We currently have the ability to reduce nutrient loads in coastal waters to levels that will not cause oxygen declines. We also know what needs to be done to reduce greenhouse gas emissions and are rapidly developing technology that will enable us to maintain good standards of living while reducing the damage we do to our planet. I am optimistic because regardless of other aspects of political philosophies, we all care about the world we leave our children and grandchildren", she emphasized.

Breitburg adds that answer to the questions how much time do we have, depends entirely on actions taken to reduce the release of greenhouse gasses into our atmosphere. While this is one of the first broad researches on the oceans, scientists have already warned us about similar effects of other phenomena in the ecosystem.More and more areas of the world's oceans are losing oxygen and turning into dead zones where nothing can survive

And what is crucial to emphasize, we still don't have the capacities needed to calculate the cumulative impact of all this phenomena, to include all the tipping points resulting in the joint influences of different phenomena, or which speed are the changes in ecosystem going to follow after passing these tipping points, and will humans be able to adapt to this changes fast enough. But, what is certain is that we have less and less time to act.

As in Croatia we are often showing too little interest in global issues, although there is no doubt we are also a part of the planetary community of living beings, it is important to add that researchers have also found many areas with declining levels of oxygen in the Mediterranean and Adriatic sea.

"Yes, there are many places around the Mediterranean, including the Adriatic, that have had problems with oxygen decline as a result of high nutrient inputs from agriculture, sewage and burning of fossil fuels", concludes Breitburg.

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Ključne riječi: science, ecology, oceans, oxygen, animals