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THE UNIVERSAL RECORD

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Scientists warn that expanding ocean “dead zones” are threatening marine ecosystems, fisheries, and coastal economies as global oxygen levels continue to decline.

By Brad Socha | May 19, 2026 | 4:47 AM EST

Large areas of the world’s oceans are steadily losing oxygen, creating expanding “dead zones” where marine life struggles to survive. Researchers monitoring coastal waters and deeper ocean regions say the phenomenon has accelerated in several parts of the globe over recent decades, raising concerns about fisheries, biodiversity, food systems, and long-term ocean stability.

The issue matters now because multiple scientific organizations, including the National Oceanic and Atmospheric Administration (NOAA), NASA, UNESCO’s Intergovernmental Oceanographic Commission, and marine institutes across Europe and Asia, are increasing monitoring efforts as warming oceans and nutrient pollution continue reshaping underwater ecosystems. Seasonal dead zones have already been recorded in areas such as the Gulf of Mexico, the Baltic Sea, parts of the Pacific Ocean, and coastal waters near major river systems.

Dead zones are regions where oxygen levels in the water become so low that many fish, shellfish, and other marine organisms cannot survive for extended periods. Some species flee these areas, while others die in large numbers. Scientists classify many of these regions as hypoxic zones, meaning dissolved oxygen concentrations drop below levels needed to sustain most marine life.

Researchers say the problem is being driven by several overlapping factors. One of the largest contributors is nutrient runoff from agriculture and urban development. Fertilizers containing nitrogen and phosphorus wash into rivers and eventually flow into oceans and coastal waters. These nutrients fuel massive algae blooms. When the algae die and decompose, oxygen in the surrounding water is consumed rapidly by bacteria.

At the same time, global ocean temperatures are rising. Warmer water naturally holds less oxygen than colder water, and increasing temperatures can disrupt the vertical mixing that normally helps circulate oxygen-rich surface water into deeper layers. Scientists say this combination of warming and nutrient pollution is intensifying oxygen decline in many regions simultaneously.

NOAA has monitored recurring hypoxic conditions in the Gulf of Mexico for decades. The area, heavily influenced by runoff from the Mississippi River basin, experiences one of the world’s largest seasonal dead zones. Measurements fluctuate yearly depending on rainfall, agricultural activity, and weather patterns, but researchers continue to document substantial low-oxygen regions that affect shrimp populations, fish migration, and commercial fisheries.

In Europe, the Baltic Sea has become one of the most studied examples of long-term oxygen depletion. Researchers have identified extensive seabed regions where oxygen levels remain critically low for prolonged periods. Some marine scientists describe parts of the Baltic as among the largest human-caused dead zones on Earth.

The problem is not limited to coastal regions. Studies published over the past several years suggest oxygen decline is also occurring in parts of the open ocean. Researchers analyzing global datasets have observed measurable oxygen losses in several ocean basins since the mid-20th century. Scientists continue studying how much of this trend is linked to natural ocean cycles, or regional human activity.

Marine ecosystems can be affected in complex ways. Fish populations may migrate toward oxygen-rich waters, potentially altering commercial fishing patterns and disrupting food chains. Coral reefs and shellfish populations may also face additional stress when oxygen decline combines with warming temperatures and ocean acidification.

Some scientists warn that prolonged low-oxygen conditions can create feedback effects that worsen environmental instability. Sediments in oxygen-poor waters can release chemicals and nutrients back into surrounding ecosystems, potentially fueling further algae growth and ecological imbalance.

Despite the growing attention, researchers say many questions remain unanswered. Some ocean regions lack sufficient long-term monitoring infrastructure, particularly in developing nations and remote waters. Scientists are also continuing to study how quickly ecosystems can recover once oxygen levels improve.

Governments and environmental agencies are responding in different ways. Several countries have introduced nutrient reduction strategies aimed at lowering fertilizer runoff into rivers and coastal systems. Some agricultural groups are experimenting with precision fertilizer application and improved land management practices designed to reduce pollution while maintaining crop yields.

Supporters of stronger environmental regulation argue that reducing runoff and limiting warming-related impacts could help slow the growth of dead zones over time. Critics of aggressive regulations sometimes raise concerns about economic costs for farmers, fishing industries, and industrial sectors. Researchers generally agree, however, that oxygen decline has become a measurable global environmental issue requiring long-term scientific observation.

Technological advances are also improving how oceans are monitored. Autonomous underwater vehicles, satellite imaging, deep-sea sensors, and AI-assisted modelling systems are giving researchers more detailed views of oxygen fluctuations across large regions. NASA and international climate agencies increasingly use combined oceanographic and satellite data to track biological activity and changing marine conditions.

Scientists emphasize that not every low-oxygen event becomes a permanent dead zone. Weather patterns, storms, seasonal currents, and local environmental conditions can sometimes temporarily restore oxygen levels. Still, many researchers believe the broader long-term trend deserves close attention as marine ecosystems continue changing.

The growing visibility of ocean dead zones reflects a wider scientific effort to understand how climate systems, industrial development, agriculture, and ecosystem health interact globally. Researchers say the oceans absorb enormous amounts of heat and carbon dioxide from Earth’s atmosphere, making them a critical indicator of broader environmental change.

As monitoring expands, scientists expect dead zones and ocean oxygen decline to remain a major focus of marine research throughout the coming decades.

Sources:

- NOAA — https://www.noaa.gov - NASA Earth Observatory — https://earthobservatory.nasa.gov - UNESCO Intergovernmental Oceanographic Commission — https://ioc.unesco.org - Smithsonian Ocean — https://ocean.si.edu - Woods Hole Oceanographic Institution — https://www.whoi.edu - Nature — https://www.nature.com - National Geographic — https://www.nationalgeographic.com

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