More "Blue Planet in Peril" news: new calculations made by marine chemists from the Monterey Bay Aquarium Research Institute suggest that low-oxygen "dead zones" in the ocean could expand significantly over the next century. Marine animals will need more oxygen to survive as more carbon dioxide created by burning fossil fuels dissolves from the atmosphere into the ocean, causing seawater to become gradually more acidic.
Researchers Peter Brewer and Edward Peltzer show that increases in carbon dioxide can make marine animals more susceptible to low concentrations of oxygen, and thus exacerbate the effects of low-oxygen "dead zones" in the ocean. Their calculations also show that the partial pressure of dissolved carbon dioxide gas (pCO2) in low-oxygen zones will rise much higher than previously thought. This could have significant consequences for marine life in these zones, making it harder for these animals to find food, avoid predators, and reproduce. Low concentrations of oxygen can have similar effects.
In trying to quantify the impacts of this "double whammy" on marine organisms, Brewer and Peltzer came up with the concept of a "respiration index." This index is based on the ratio of oxygen and carbon dioxide gas in a given sample of seawater. The lower the respiration index, the harder it is for marine animals to respire.
In the past, marine biologists have defined "dead zones" based solely on low concentrations of dissolved oxygen. Brewer and Peltzer hope that their respiration index will provide a more precise and quantitative way for oceanographers to identify such areas. Tracking changes in the respiration index could also help marine biologists understand and predict which ocean waters are at risk of becoming dead zones in the future.
Previous studies have indicated that such oxygen minimum zones may expand over the next century. Brewer and Peltzer's research suggests that the effects of this expansion will be even more severe than previously forecast.
The number of oxygen-starved "dead" zones is growing in oceans around the globe. The situation is so bad many regions can now barely sustain marine life. In addition to Brewer and Peltzer's studies, other scientists say huge amounts of nitrogen-containing nutrients from farm fertilizers get most of the blame.
Since the 1960s, the number of dead zones worldwide has doubled every decade. Researchers say there are now about 400 of them. All together, they cover an area about the size of the state of Oregon. Although this is small compared to the total surface area of the oceans, it's big enough to damage marine ecology and hurt commercial fishing and shellfishing.
Huge amounts of pollution from industry and runoff from cities get dumped into coastal waters. This triggers a chain reaction that robs water of oxygen and makes it harder for living things to survive.
The pollutants provide nutrients that feed the growth of algae. As the algae dies and decays, bacteria levels increase. The bacteria gobble up much of the ocean's oxygen. This kills fish and other marine organisms. It also hurts people that depend on these resources for food or to make a living.
The Gulf of Mexico has one of the biggest dead zones. The lifeless zone stretches from the mouth of the Mississippi River to the Texas border. It now covers an area of nearly 8,000 square miles (20,000 square km). Other dead zones have appeared in the Chesapeake Bay, the Pacific Northwest, and off the coast of South Carolina.
Dead zones have appeared off the coasts of South America, Britain, China, Norway, Japan, Portugal, Ghana, Australia, and New Zealand in recent years. The dead zones tend to get worse in the summer months. But over a period of several years, they can wipe out species from the zone permanently.
Posted by Casey Kazan.
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