Dead zones are low-oxygen, or hypoxic, areas in the world’s oceans and lakes. Because most organisms need oxygen to live, few organisms can survive in hypoxic conditions. That is why these areas are called dead zones. Several recently released studies have documented the accelerating changes to Earth’s oceans as a result of climate change, including a reduction in the oxygen content, which is threatening vast swaths of marine life.

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Dead zones are well-known off the western coasts of North and South America, Namibia and India in the Arabian Sea. Recently a dead zone has been found in Bay of Bengal, India.

Causes for formation of dead zones:

• Eutrophication: An increase in chemical nutrients in the water, leading to excessive blooms of algae that deplete underwater oxygen levels. Too many nutrients are a form of pollution that lead to the death of organic food sources and destroys natural habitats.
• Algal bloom: Overgrowth of algae, which then sink and decompose in the water. The decomposition process consumes oxygen and depletes the supply available to healthy marine life. Excess nitrogen and other chemicals in the ocean lead to extreme imbalances underwater, with algal bloom resulting from the existence of these elements and being a major contributor to the creation of dead zones.
• Agricultural runoff: Nitrogen and phosphorous from chemical fertilizers lead to eutrophication.
• Climate change: Warm water is unable to hold as much dissolved gas. Global warming also melts ice, which releases fresh water that rests on the surface of the more dense salt water generally found in oceans. This layer can keep water at the surface and in the ocean’s depths from mixing, which is the only way that the deeper parts of the ocean have their oxygen stores replenished.
• Emissions: Sewage, vehicular and industrial emissions add to the nutrient content of ocean. Oil spills in the ocean usually happen when an ocean oil rig springs a leak or when an ocean going tanker (carrying oil) wrecks.
• Oceanographic phenomenon: Stagnant water in enclosed water bodies, coastal upwelling, ocean and wind current patterns effect the formation of dead zones.

Consequences of dead zones:

• It forces species to migrate to more oxygen-rich areas, exposing them to new predators while disrupting the already existing ecosystem. Polar regions in recent years, for example, have suffered an invasion of species from lower latitudes seeking to escape increasingly inhospitable areas.
• Oxygen-poor waters make it more difficult for male fish to produce sperm and for those sperm to be as mobile as in normal waters. Poses long-term threats to the sustainability of sea creature populations in areas with decreased oxygen content.
• Impairing animals’ ability to see and hear, impeding their ability to find food and escape from predators.
• Hundreds of millions of human beings who use fish as a primary source of food and make their livelihood from fishing will suffer.

Way forward:

• Better practices and accountability must be put in place to protect the ocean. A major step would be to stop letting so many chemicals find their way into the ocean.
• As humans, we need to pay attention to where we let our sewage direct itself and to what we allow to absorb into the ground.
• Treating the ocean like a large trash negatively affects us all because it creates toxicity.
• Raise awareness by explaining to others the importance of keeping the ocean clean can help to encourage positive habits.
• A spur of eco-friendly activities like proper waste disposal, addressing climate change, organic farming, recycle and reuse, wetlands and floodplains conservation are needed.
• Innovative measures like nutrient trading on lines of carbon trading can go a long way in solving the problem