Dead Zones

By Ian Teñido


The occurrence of such zones is considered natural but scientists have, in the recent years, attributed most dead zones to human activity. While there are many chemical, biological, and physical factors that lead to creation of dead zones, excessive nutrient loading is the primary cause of those zones created by humans. The excess nutrients run off from agricultural fields or farm lands are piped as waste water into coastal areas or rivers; these nutrients then stimulate the fast growth of algae causing algae bloom. When this much algae starts to decompose in water, a huge amount of oxygen is utilized in the process leading to an automatic oxygen depletion in the area. This makes any form of life in the area unbearable and all the zooplanktons and phytoplankton are exposed to immediate suffocation. Only mobile life forms can survive by swimming away to areas with adequate oxygen.

These dead zones occur anywhere in the world and no one oceanic region can consider itself immune to this condition. In fact, within the coastal zones of the U.S, there are many dead zones; particularly along the East Coast, the Great Lakes and Gulf of Mexico. Actually, the largest second dead zone in the world is located in the Northern Gulf of Mexico. Of course, the largest now being the Gulf of Oman. The Gulf of Oman spans 70,000 square miles; nearly the size of Florida! This area has been off-limits due to the political instability in the Arabian region and thus the Baltic Sea has falsely been considered the largest for some years since its discovery. It should be noted that the Arabian Sea is home to numerous species of fish including those which are tolerant of low-oxygen conditions. The recent studies in the Gulf of Oman using the Sea gliders revealed that the level of oxygen depletion in the gulf is far worse than imagined…

 Global map showing the regions where dead zones in aquatic systems are persistent problems. Notice that most of the dead zones are located in regions of high population density, where runoff of nitrogen and phosphorus fertilizers are causing excessive growth of algae in surface waters.Global Change

A quick look into the historical studies on dead zones show that in the 1960s there were only 49 discovered dead zones; today, there are more than 400 dead zones across the planet’s oceans! Well, it started off as a small matter but for now, most researchers and data observed otherwise. The social, economic and environmental aspects of life are, all the same, affected by this alarming phenomenon. Let’s look at it this way, more than 212,000 metric tons of food are lost to hypoxia in the Gulf of Mexico alone; if this is translated to more than 400 others, we are talking about billions of metric tomes of food. Now, when this is mirrored down to communities and economies that depend on fisheries, a disaster apparently surrounds the atmosphere.

And finally, well how is this connected to Climate change? This question is best answered when we zero down to the connection between eutrophication and climate change. With increased extreme weather events, there are also increased flooding which then leads to excessive nutrient loading in the lakes and oceans. This takes us back to the top where nutrient loading leads to eutrophication which then turns such areas into dead zones as soon as decomposition of the massive algal blooms begin. Therefore, with predicted increase in climate change and global warming, we should expect more dead zones with its associated impacts.



NOAA (n.d.). What is a Dead Zone? Retrieved from

Spector, D. (2013). Our Planet Is Exploding With Ocean Dead Zones. Retrieved from

Weisberger, M. & Writer, S. (2018). Massive ‘Dead Zone’ in the Arabian Sea is the Biggest in the World. Retrieved from

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