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Explained: What are dead zones in the ocean and what do they mean

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The planet is reeling from the effects of the sustained global increase in temperatures. And Oceans, particularly, are susceptible to climate change. From increasing ocean acidity to the collapse of the thermohaline current that regulates the temperatures of the globe, climate change is causing significant effects on oceans. But another problem that is increasingly plaguing global water bodies is one that is not so obvious and well known—dead zones. 

Explained: What are dead zones in the ocean and what do they mean
Oceans are becoming a graveyard of sea creatures as the levels of oxygen plummet to levels so dangerously low that sea creatures have started to flee. And if they can't flee, they die.
Francis Chan, a biologist at Oregon State University had gone to research a strange occurrence at the coast of Oregon in 2002. Fishers reported pulling pots of dead fishes. In fact, an octopus climbed up the ropes of fishers to escape from something. No one could tell what.
While researching for the culprit, Chan discovered swaths of low-oxygen zones, never seen before. These low levels of oxygen, also called hypoxic zones, had never happened so close to the shore before.
Hypoxic zones form off the coast of Oregon every summer. In fact, due to the recurrence has it now has a term, 'hypoxic season', akin to wildfire and hurricane season.
Chan says climate change has exacerbated this effect, with these hypoxic zones morphing into dead zones. These dead zones lack oxygen completely, killing creatures that cannot swim away.


What are dead zones in oceans?
Dead zones in oceans are areas or pockets of water that have critically low levels of oxygen. This causes aquatic life to either flee or perish as they suffocate to death and litter the ocean floor.
Though dead zones are a bit of a misnomer. Since the oceans are so vast and so deep, dead zones often occupy only a fraction of the total depth, area and volume. The scientific term for the low concentration of oxygen in water is hypoxia. 
"Less oxygen dissolved in the water is often referred to as a “dead zone” because most marine life either dies or if they are mobile such as fish, leave the area. Habitats that would normally be teeming with life become, essentially, biological deserts,” says the US National Oceanic and Atmospheric Administration (NOAA). 
What causes dead zones?
Ocean hypoxia is essentially caused by two mechanisms—increased ocean temperature and currents and wind patterns. Warmer water can dissolve more solids within it, but this comes at a cost of lower solubility of the gas. The warmer the ocean water gets, the lower the solubility of oxygen becomes. As a result, we start to get low concentrations of oxygen in the water. 


The effect is compounded by currents and wind patterns. Winds like upwelling winds that flow from the shore to the ocean can hit hypoxic areas of the ocean and intensity the effect. This causes the hypoxic zones to become more well defined and critically desaturated with oxygen.
"We know that climate change is pulling these two levers, and we’re just seeing the consequences of that,” Chan said. “I think I say with some reticence that, when I think about what the future of the oceans looks like, along not only Oregon but the west coast (of USA), I think the science is really pointing us to an ocean that is much more prone to episodes of hypoxia."
What does this mean?
With the continuing global increase in temperature, the presence of such hypoxic zones will continue to increase. Chan’s research has found that oceans around the globe have been losing oxygen for over 5 decades.
Hypoxic zones are also expected to increase in size and frequency as the 21st century continues on. And as they do, they’ll cause large scale ecological damage more and more frequently.
Lowered quantity and quality of aquatic life can threaten millions of livelihoods and push many more into food scarcity.
The recent IPCC Assessment Report summarising the latest information about global warming flagged that the Indian Ocean is warming faster than other oceans. The ocean supports large quantities of marine life that are used to sustain populations of billions of people across Asia, Africa and Australia with seafood. As ‘dead zones’ eradicate this careful ecosystem, these areas will be threatened with growing hunger crises. 


 
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