• Bryony Lewis

The Ocean is Suffocating

Ocean Dead Zones are increasing at an alarming rate, robbing marine life of oxygen.

What is an ocean dead zone?

A “dead zone”, also known as hypoxia, is a term that describes an area in the ocean that has such low levels of oxygen in water that animals can no longer survive. They’re understandably considered to be biological deserts, because all life either dies or migrates away.

Dead zones develop naturally through various combinations of factors but the primary explanation usually involves nutrient deterioration, caused by humans. Waste water containing surplus nutrients from various sources will run into and through water bodies that will subsequently be invaded and overrun by algae. Through its eventual decomposition, the algae will consume the oxygen available and leave the native marine life to suffocate or migrate.

According to National Geographic, when water reaches two parts per million or less of oxygen, any roving wildlife like crustaceans or fish will migrate away, which can negatively impact the food chain. In addition, stationary wildlife will either cease to grow or die in these hypoxic conditions. Even those living near to hypoxia can be altered, with zebrafish being just one example of a fish known to have its testosterone levels affected by hypoxia, creating male-biased generations (Rudolf S. S. Wu, 2009). This can, ultimately, wipe out a species if escalated.

While the dead zones are not often given coverage in mainstream news, there is not one area of the ocean that is exempt from its potential effects. And although they can occur naturally, our agricultural practices are to blame for a large proportion of them. Since 1950, the number of dead zones has increased from fewer than 50 to over 500. Therefore, it is a crucial aspect of today’s ecology that we need to be aware of, in order to stop more forming and decrease the number of those we already have.

The Gulf of Mexico Hypoxia

For over thirty years now, scientists have studied the dead zone in the Gulf of Mexico that occurs annually. They came to the conclusion that nutrients from fertilisers have run into the sewage in the Mississippi and through into the Gulf. The surplus nutrients have fed an overrunning population of algae and depleted the area of its oxygen. In addition, due to the layering of the freshwater and salt water as it enters the sea, it is even more difficult for the limited oxygen to mix. In July 2017, this area was considered the largest dead zone ever recorded in the region (8, 776 square miles) and many scientists believe this is largely due to human activity. In recent years, scientists have even discovered hypoxic regions larger than this. At 63,000 square miles, the world’s largest dead zone is in the Arabian Sea and is seven times larger than the Gulf of Mexico’s hypoxia.

What are the causes?

This is indicative that our agricultural practices, including our use of pesticides, herbicides and fertilisers or industrial chemicals need to be reduced, abolished or at least controlled safely. This includes the meat production industry, as organisations such as Mighty Earth have stated that ‘these dead zones will continue to expand unless the major meat companies that dominate our global agricultural system start cleaning up their supply chains to keep pollution out of our waters.

Our ever-increasing burning of fossil fuels has a monumental impact on the creation and increase of these dead zones. Warmer water is known to carry less oxygen than cold water, and, incidentally, the warmer the water, the faster marine mammals must breathe and the faster the oxygen depletes. So, with increased floods, natural disasters, increased food production or farming and water temperatures, caused by climate change, we are facing a monstrous crisis in our oceans.

A vicious cycle can also occur within the dead zones, whereby microbes that breed in these areas can often give off large amounts of nitrous oxide, which is three hundred times more powerful than CO2. Decreasing this hypoxia can decrease the permeation of this gas and reduce our footprint.

Can we turn it around?

Yes. It is possible to save the oceans before it’s too late. London once had dead zones in the Thames, but through careful changes in sewage and farm practices, these dead zones disappeared. It goes to show that this is an issue we can clear up. Small actions (managing runoff waste, for example) that alleviate the effects or creation of dead zones will increase the oxygen levels in the oceans and, in turn, increase biodiversity in these areas. This biodiversity, when appearing in the tens to hundreds of thousands of miles of hypoxia, will be a tremendous and vital element in our attempts to slow climate change.

Three ways in which the Gulf Coast Preservation Society have presented solutions to the hypoxia problem is through these three means:

  1. Voluntarily stop fertliser and waste runoff into lakes, rivers and streams

  2. Enact laws to prevent this from happening

  3. Build water treatment plants to prevent animal and human waste from entering the water sources.

Perhaps, on a much smaller scale, too, we can think about what we are putting down our drains. Look at the labels on products you use to ascertain if they are made to enter water sources before you decide to dispose of them this way. If a label doesn’t inform you, don’t risk it: keep it out of the oceans.


National Ocean Service

The Guardian (online)

Gulf Coast Preservation Society

National Geographic


Science Direct

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