New! Sign up for our free email newsletter.
Reference Terms
from Wikipedia, the free encyclopedia

Dead zone (ecology)

Dead zones are hypoxic (low-oxygen) areas in the world's oceans, the observed incidences of which have been increasing since oceanographers began noting them in the 1970s. The term could as well apply to the identical phenomenon in large lakes. Aquatic and marine dead zones can be caused by the process of eutrophication, triggered by an excess of plant nutrients (nitrogen and phosphorus) from fertilizers, sewage, combustion emissions from vehicles, power generators, and factories. In a cascade of effects, the nutrients trigger a bloom of phytoplankton at the bottom of the marine food chain, allowing zooplankton to proliferate. As phytoplankton and zooplankton die and sink below the photic zone where photosynthesis can occur, a bloom of natural bacterial degradation exhausts the water's dissolved oxygen. Low oxygen levels recorded along the Gulf Coast of North America have led to reproductive problems in fish involving decreased size of reproductive organs, low egg counts and lack of spawning.

 

In March 2004, when the recently established UN Environment Programme published its first Global Environment Outlook Year Book (GEO Year Book 2003), it reported 146 dead zones in the world's oceans where marine life could not be supported due to depleted oxygen levels. Some of these were as small as a square kilometre (0.4 mi²), but the largest dead zone covered 70,000 square kilometres (27,000 mi²). A 2008 study counted 405 dead zones worldwide.

Aquatic and marine dead zones can be caused by an increase in chemical nutrients (particularly nitrogen and phosphorus) in the water, known as eutrophication. These chemicals are the fundamental building blocks of single-celled, plant-like organisms that live in the water column, and whose growth is limited in part by the availability of these materials. Eutrophication can lead to rapid increases in the density of certain types of these phytoplankton, a phenomenon known as an algal bloom.

Related Stories
 


Earth & Climate News

July 29, 2025

Researchers are exploring AI-powered digital twins as a game-changing tool to accelerate the clean energy transition. These digital models simulate and optimize real-world energy systems like wind, solar, geothermal, hydro, and biomass. But while ...
Deep in Serbia's Jadar Valley, scientists discovered a mineral with an uncanny resemblance to Superman's Kryptonite both in composition and name. Dubbed jadarite, this dull white crystal lacks the ...
Mesopelagic fish, long overlooked in ocean chemistry, are now proven to excrete carbonate minerals much like their shallow-water counterparts—despite living in dark, high-pressure depths. Using the deep-dwelling blackbelly rosefish, researchers ...
For over two decades, satellites have quietly documented a major crisis unfolding beneath our feet: Earth's continents are drying out at unprecedented rates. Fueled by climate change, groundwater ...
Air pollution isn't just bad for your lungs—it may be eroding your brain. In a sweeping review covering nearly 30 million people, researchers found that common pollutants like PM2.5, nitrogen ...
A new eco-friendly plastic called LAHB has shown it can biodegrade even in the extreme environment of the deep ocean, unlike conventional plastics that persist for decades. In real-world underwater testing nearly a kilometer below the surface, LAHB ...
In 2023, the world’s oceans experienced the most intense and widespread marine heatwaves ever recorded, with some events persisting for over 500 days and covering nearly the entire globe. These ...
Imagine concrete that not only survives wildfires and extreme weather, but heals itself and absorbs carbon from the air. Scientists at USC have created an AI model called Allegro-FM that simulates billions of atoms at once, helping design futuristic ...
Scientists have discovered that pairing bread wheat with a special soil fungus can significantly enhance its nutritional value. This partnership leads to bigger grains rich in zinc and phosphorus—without increasing anti-nutrients that block ...
Scientists in Svalbard were shocked to find rain and greenery instead of snow during Arctic winter fieldwork. The event highlights not just warming—but a full seasonal shift with major consequences for ecosystems, climate feedback, and research ...
A colossal 7.7 magnitude earthquake rocked central Myanmar in March 2025, marking the strongest quake in over a century. What makes this event groundbreaking isn't just the seismic power, it's the ...
Ancient river landscapes buried beneath the East Antarctic Ice Sheet have been uncovered by radar, revealing vast, flat surfaces formed over 80 million years ago before Antarctica froze. These hidden features, stretching across 3,500 kilometers, are ...

Latest Headlines

updated 12:56 pm ET