Scientists recently said that they have evidence that ocean dead-zones are real. They reported that they discovered several zones that are hostile to marine forms of life in remote areas in the tropical North Atlantic. Their findings were published in last week’s issue of the open-source scientific journal Biogeosciences.
Researchers wrote in their paper that the marine dead zones are 100-mile long patches of ocean, which are so incredibly deprived of oxygen that any marine creature which attempts to cross them suffocates and dies.
The dead zones were detected within huge oceanic whirlpools also called eddies. Eddies usually appear for no reason in open oceans and some of them continue to spin for months. Scientists dubbed these areas “dead-zones” because their waters have no or little oxygen, making life unable to thrive. Marine creatures that are unfortunate enough to enter these zones have only two options – quickly get out or die.
But there are different types of dead-zones. Usually, dead-zones form across the coastline in shallow waters for various reasons. Some of them occur because the body of waters does not receive any fresh oxygen input from streams, while others are caused by pollution. One of the most notable dead zones across the planet is the one in the Gulf of Mexico. There, dead zones usually occur every summer through a complex but natural mechanism.
Mississippi River Delta carries huge amounts of nutrients to the gulf where large algae blooms feel stimulated to multiply and thrive on the generous influx of nutrients. But algae eventually end up as food for microorganisms, which in return generate huge amounts of waste. Other microorganisms thrive on waste but they consume the reserves of oxygen in the process.
On the other hand, the newly found dead zones have a different story to tell. In the middle of Atlantic there’s plenty of water around and no algae invasion can be held accountable for the low levels of oxygen. Researchers explained that eddies generate low-oxygen bodies of water as they swirl around them. These marine whirlpools usually confine a central body of water just like a wall does. As water cannot leak, nor does new water can get in, the area ends up as a dead zone when oxygen levels fall to alarming low levels.
“The fast rotation of the eddies makes it very difficult to exchange oxygen across the boundary between the rotating current and the surrounding ocean,”
They also argue that the swirling movement generates a shallow surface layers on top of the entrapped body of water where algae blooms can thrive. But as plants continue to multiply, oxygen content at the center of the eddy starts to slowly vanish.
The authors of the findings reported that they performed several tests on water samples collected from those areas. They found that in some dead zones water contained no oxygen, while in others they found a maximum concentration of 0.3 milliliter of dissolved oxygen/liter of water.
According to previous studies, the lowest recorded oxygen level in North Atlantic was 1 milliliter.
Dead zones are dangerous because thy can impact marine wildlife in the most life-threatening ways. But because they are on a constant move they can also affect coastal communities from Cape Verde, researchers believe.
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