Increase of killer ocean "dead zones" caused by global warming

Oceanographers first began recording dead zones--areas of hypoxic low-oxygen in deep waters of ocean bodies, in 1970—when they counted 146 dead zones.

Currently, in a study released in 2008, scientists reported up to 405 dead zones.

Most aquatic life cannot survive in an environment with depleted oxygen. These killer zones often have bodies of dead crustaceans, crabs, fish, and other marine animals—littered on the ocean floor.
Scientists believe the increase in global warming has caused the spread of ocean dead zones throughout the Pacific, Atlantic, and Indian oceans.

Quite simply, warmer water increases CO2 concentration and holds less oxygen.

“The real surprise is how this has become the new norm," said Jack Barth, an oceanography professor at Oregon State University. "We are seeing it year after year."

The change in the ocean’s fragile ecosystems, are equally affected by warmer temperatures, which impacts the food system. It and can cause a trapping cap-like affect in the top layer of the ocean.

The warmer water has a negative impact on the natural circulation of colder, more oxygenated and nutrient rich water. This process is known as up-welling. Without oxygen and nutrients, the ocean ecosystem in such an area would fail to survive.

According to the Global Environment Outlook Year Book, published by the UN Environment Program in 2004, dead zones range in size from small to gigantic. The smallest was measured at 0.4 mile, with the largest covering over 27,000 miles.

Furthermore, studies show that some areas off the California coast have recorded oxygen depletion of 20% over the past 25 years, while other regions may have experienced a declined by one-third over 50 years.

Research has shown that many ocean dead zones occur near populated coastlines, where aquatic life is most concentrated, resulting in the death of thousands of marine creatures from small krill to larger fish.
The coasts of Washington and Oregon have some spots, with an ocean floor piled high with dead sea-stars, crustacean carcasses, and dying anemone colonies. The decay produces a bacteria-rich and potentially poisonous condition, which compounds the lethal affect.

“The depletion of oxygen levels in all three oceans is striking," said Gregory Johnson, an oceanographer with the NOAA Administration in Seattle.

Scientists, including Barth and others say the changes coincide with current climate change models. Studies also have found that oceans are increasingly more acidic as C02 and other greenhouse gases are absorbed.

Scientists are unsure how dead zones affect larger marine animals, like whales, sea lions, and dolphins, because they are big and fast enough to move out of danger, but bottom-dwelling creatures and slower moving aquatic life will always be at greater risk.

Some species will not be affected by low oxygenated water, like jellyfish and squid.

"It's a large disturbance in the ecosystem that could have huge biological changes," said Steve Bograd, an oceanographer at NOAA's Southwest Fisheries Science Center in Southern California.

In addition, dead zones have developed in larger lakes with the same characteristics.

Pollution and runoff pours into rivers that empty into oceans. One of the largest aquatic life killer zones is in the Gulf of Mexico, near the mouth of the Mississippi River.