What Are Ocean Dead Zones, and Why Are They Becoming More Common?

In a groundbreaking study, scientists have found that the number of deoxygenated zones in our oceans has risen sharply over the past several decades.

The Global Ocean Oxygen Network, a panel created by the UN Intergovernmental Oceanographic Commission, conducted this new study – the first to review existing data with the intent to gain a broad overall view of the situation.

The study examines the causes of these low-oxygen environments, as well as their impact on wildlife.

Researchers found that the number of so-called zero-oxygen regions has increased fourfold over the past 50 years. In addition, coastal waters have seen a 10-fold increase in low-oxygen sites since 1950. And this won’t come as news to anyone who’s followed the Gulf of Mexico’s dead zone, which continues to grow at an alarming rate.

Indeed, researchers believe that without action this trend will continue and the number of low-oxygen zones will only grow.

What are dead zones?

Dead zones are large areas of water that, for a combination of reasons, no longer have enough oxygen to support life. They usually occur in our oceans, but they can also manifest in places like coastal areas, rivers and lakes.

There are several root causes for these dead zones, but they often involve an increase in certain chemicals, leading to algae blooms that rapidly use up the oxygen in the water. When this happens, fish and other marine life can no longer survive.

What causes ocean dead zones?

Low oxygen zones can occur naturally, but their prevalence has increased rapidly since scientists first took interested in dead zones in the 1970s.

Hypoxia, a deficiency of oxygen, can result from nitrogen and phosphorous run-off from agricultural sites. Other contributing factors include sewage and fossil fuel emissions, which can promote algae growth by changing the water’s chemical composition.

Rising ocean temperatures play a significant role too. Due to man-made climate change, ocean temperatures have risen significantly since the Industrial Revolution. Warmer oceans do not hold on to oxygen as efficiently, and the environment is particularly well suited for algae blooms.

We can’t ignore ocean dead zones any longer

The researchers in this study suggest that current government policy is ignoring ocean dead zones and writing them off as low-priority action points, despite the serious risks they pose.

Denise Breitburg, of the Smithsonian Environmental Research Center and a lead researcher in this review, explained:

Major extinction events in Earth’s history have been associated with warm climates and oxygen-deficient oceans. Under the current trajectory that is where we would be headed. But the consequences to humans of staying on that trajectory are so dire that it is hard to imagine we would go quite that far down that path.

However, Breitburg is also clear that we can act to safeguard our waters. “This is a problem we can solve,” Breitburg continues. “Halting climate change requires a global effort, but even local actions can help with nutrient-driven oxygen decline.”

Our fishing stocks are already under threat, but as low-oxygen and no-oxygen zones increase, marine life will feel the pressure. This will lead to large swathes of the ocean where fish cannot survive. And with higher population density in certain areas, the fish will be more vulnerable to predators.

Ocean dead zones may also interrupt key migration routes for marine species, potentially resulting in severe population decline.

How can we prevent dead zones?

Some of the key strategies for fighting ocean dead zones actually take place on land — and as interventions go, they’re relatively low cost.

One important step is to reduce agricultural run-off by helping farmers build and utilize two-stage drainage ditches. We can further support this kind of barrier method by restoring wetland and forest sites, particularly if they are close to major waterways. This enables nature to soak up the run-off that might otherwise promote an algae bloom.

We can also tighten regulations on factories to reduce fossil fuel emissions.

On a personal level, we can opt to use fertilizers sparingly, use non-toxic alternatives for household cleaners and conserve water and power where possible.

Obviously, these small acts on their own will not save marine biodiversity, but combined with policy change, we really could halt the growth of ocean dead zones.

Take Action

One of the biggest reasons for the Dead Zone are giant meat companies like Tyson which are driving water pollution throughout the country. Tell Tyson to clean up its pollution. 

Photo Credit: samsommer/Unsplash

51 comments

Amanda M
Amanda Myesterday

Thanks for sharing

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Amanda M
Amanda Myesterday

Thanks for sharing

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silja s
silja salonenyesterday

we are killing ourselves

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Brad W
Brad W.yesterday

We've been destroying agriculture via cheap prices, caused economically by chronic free market failure, and caused politically by the reduction (1953-1995 and elimination (1996-2018) of market management policies and programs (price floors and inventory reductions, as needed to balance supply and demand). This subsidized CAFOs to take the value-added livestock off farms, leading to the loss of sustainable crop rotations, including sod pasture/hay. We must restore supply reductions that incentivize cutting fertilizer use.

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Carole R
Carole Ryesterday

Thanks for the information.

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Shirley S
Shirley S1 days ago

Interesting & alarming news.

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Amanda M
Amanda M2 days ago

Thanks for sharing

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Amanda M
Amanda M2 days ago

Thanks for sharing

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Misss D
Misss D2 days ago

The book ‘Animal Factory’ by David Kirby addresses the whole issue of dead zones caused by run off from cattle and pig farming very well. When these animals are farmed intensively, they create a huge amount of waste (ie urine and faecal matter) that cannot be dealt with adequately onsite. Very often, this waste is allowed to contaminate local streams and rivers which themselves become dead zones and then flow into the sea. I have signed the petition to Tyson but I also do not eat beef or factory farmed pig products. A national reduction in the amount of red meat, and probably white meat, eaten in the USA and other countries would have a huge effect in reducing the number of dead zones.

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Danuta W
Danuta W3 days ago

Thanks for sharing

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