Hypoxia- Dead Zones

News related to hypoxia.

1. World's Largest Dead Zone Suffocating Sea.

James Owen in Stockholm

for National Geographic News

Published March 5, 2010

This story is part of a special series that explores the global water crisis. For more clean water news, photos, and information, visit National Geographic's Freshwater Web site.

"Eagle!" The shout goes up as a great shadow sweeps over our boat. The white-tailed eagle makes its descent to one of the 24,000 islands that make upSweden's pine-covered, rocky Stockholm Archipelago.

The tourists on board for this nature tour in August 2009 mostly miss the photo op. But local wildlife expert Peter Westman, of the conservation group WWF Sweden, assures the group that there will be others.

Numbers of this once-threatened predator have soared from 1,000 to more than 23,000 in the Baltic Sea (map) since pollutants including DDT, an eggshell-thinning pesticide, and PCBs, chemical compounds used in electrical equipment, were banned in the 1970s, Westman said.

But there is a new danger to the eagle and many other marine species: An explosion of microscopic algae called phytoplankton has inundated the Baltic's sensitive waters, sucking up oxygen and choking aquatic life.

Though a natural phenomenon at a smaller scale, these blooms have recently mushroomed at an alarming rate, fed by nutrients such as phosphorous and nitrogen from agricultural fertilizers and sewage. When it rains, farm fertilizers are washed into the sea. Sewage-treatment facilities also discharge waste into the Baltic ecosystem.

As a result, the Baltic is now home to seven of the of the world's ten largest marine "dead zones"—areas where the sea's oxygen has been used up by seabed bacteria that decompose the raining mass of dead algae.

"We’ve had enormous algal blooms here the last few years which have affected the whole ecosystem," Westman said.

Overfishing Adding to Algal Blooms

Overfishing of Baltic cod has greatly intensified the problem, Westman said. Cod eat sprats, a small, herring-like species that eat microscopic marine creatures called zooplankton that in turn eat the algae.

(Related: "Overfishing is Emptying World's Rivers, Lakes, Experts Warn.")

So, fewer cod and an explosion of zooplankton-eating sprats means more algae and less oxygen.

This vicious cycle gets worse as the spreading dead zones engulf the cod’s deep-water breeding grounds, he added.

The algal blooms, which can be toxic to animals and human swimmers, leave behind an ugly layer of green scum that fouls tourist beaches and starves seaweeds of light.

"Other species have taken the place [of seaweed], which don’t provide as good habitats for fish," especially juveniles, Westman said. "In the past couple of years common fishes like pike and perch have had virtually no reproduction in the inner part of the archipelago."

Too Late to Save the Baltic Sea?

Back in Stockholm, it's World Water Week, the annual global meeting on water issues organized by the Stockholm International Water Institute. On a conference room wall is a satellite image of the Baltic Sea, its deep blue edges giving way to a swirling, milky center that shows the algal blooms.

World Water Week attendees are pushing a new action plan called the Baltic Sea Strategy. The European Union-led initiative will attempt to coordinate the efforts of the eight EU members within the nine Baltic states—not including Russia—to revitalize their shared sea.

While the speakers all agree "it’s time for action," they don’t sound optimistic.

"It might well be too late," said Søren Nors Nielsen of the University of Copenhagen.

The planet’s youngest sea at less than 10,000 years old, the Baltic is unique in that it formed after the last ice age. It's also one of the world’s largest bodies of brackish water.

"Experience tells us such a system is almost impossible to predict," Nielsen said.

The Baltic Sea's unusual mix of fresh water and marine species means it's also especially vulnerable to environmental changes. "Evolution didn’t have time to develop an ecosystem able to tolerate flux," Nielsen explained.

(Related: "Viking Shipwrecks Face Ruin as Odd 'Worms' Invade.") 

"Sea of Laws"

Water-law attorney Megan Walline of the Stockholm International Water Institute, who spoke at the Baltic Sea presentation, said there's already "a sea of laws" for dealing with human activities that threaten the Baltic.

Too numerous to list, they include existing EU directives that cover nutrient pollution and illegal fishing. The laws are there, they just need to be implemented, she said.

For his part, WWF’s Westman hopes the new EU strategy will at least turn the Baltic into "a kind of test area for enforcing and implementing the directives." For instance, the plan calls for phasing out phosphates in laundry and kitchen detergents, and putting in place more sustainable fishing regulations.

Even so, "There are no quick fixes, unfortunately," Westman concludes, reaching for his binoculars.

Seems it’s back to the eagles for now.

2. Global Warming to Create "Permanent" Ocean Dead Zones?

Ker Than 
for National Geographic News
January 28, 2009Fish and other marine life could be left gasping for breath in oxygen-poor oceans for thousands of years to come if global warming continues unchecked, scientists warn in a new study.

While previous studies have established a link between climate change and low-oxygen areas known as "dead zones," new computer simulations by Danish researchers suggest the dead zones could persist for millennia and lead to a considerable purge and restructuring of ocean life.
"Any increase in dead zones from global warming will last for thousands of years. They will be a permanent fixture" of our oceans, said lead researcher Gary Shaffer of the University of Copenhagen.

The new model tracked the effects of global warming on ocean dead zones in the eastern Pacific and northern Indian oceans for the next 100,000 years.

Dead zones currently make up less than 2 percent of the world's ocean volume. The model predicts that global warming could cause dead zones to grow by a factor of ten or more by the year 2100.

In the worst-case scenario, dead zones could encompass more than a fifth of the world's oceans, the team says.

(Related: "Ocean Dead Zones Growing; May Be Linked to Warming" [May 1, 2008].)

Waves of Death

While many dead zones today are transient and reversible, those expanded by greenhouse gases such as carbon dioxide would last for millennia, Shaffer said.

"Quite a bit of the carbon dioxide emitted by human activity into the atmosphere will stay there for tens of thousands of years."

"Thus global warming, ocean warming, and oxygen depletion will also have this long time scale," he said.

According to the model, global warming will reduce the oceans' ability to store oxygen while simultaneously decreasing the amount of oxygen available in the ocean depths.

Warmer water can hold less oxygen compared with cooler waters. "As the ocean is heated by a warmer atmosphere, oxygen concentrations decrease, Shaffer said.

Furthermore, as Earth's icy poles gradually transform into open oceans, new organisms, from plankton to shellfish, will move in.This biological boom further decreases the available oxygen in the ocean interior because when organisms die, their bodies drift to the sea floor and are broken down by bacteria which require oxygen to survive.

If biological production in the ocean increases, so too does the population of oxygen-consuming bacteria, said Shaffer, whose research is detailed in the current issue of the journal Nature Geoscience.

Doomsday Scenario

Francis Chen is a marine ecologist at Oregon State University who was not involved in the study.

By modeling how the ocean system will respond to and in turn, influence climate change, Shaffer and his colleagues have provided a means of systematically looking at how multiple factors will play out, Chen said.

"Such studies are an important tool for examining what the future may hold for the world's oceans," he said.

Paul Wignall, a professor of paleoenvironments at the University of Leeds in the United Kingdom, called the new predictions "the doomsday scenario for the oceans."

Wignall, who was not involved in the current research, has studied the Permian extinction 250 million years ago.

Also known as the "Great Dying," the event is considered the worst mass extinction in Earth's history, affecting 95 percent of all marine species. Growing evidence suggests global warming and oxygen-poor oceans—possibly stemming from volcanic eruptions—were major factors.

3. Ocean dead zones increasing at alarming rate, warns United Nations.

(NaturalNews) A report issued last week by the United Nations Environment Programme (UNEP) has found that the number of oxygen-starved ocean "dead zones" has increased by more than a third over the last two years.Dead zones form when microscopic marine plants called phytoplankton -- which act as the backbone of marine food chains -- explode in mass, attracting oxygen-consuming bacteria. The oxygen depletion, called hypoxia, kills off large quantities of fish, oysters, sea grasses and other forms of ocean life.

Marine scientists say phytoplankton levels naturally swell and die off, but abnormally large die-offs have been observed since the 1970s. The UNEP report says extremely high marine levels of certain nutrients -- such as phosphorus and nitrogen from fertilizers, sewage, animal wastes and other sources -- can cause dead zones.

Marine biologist Robert Diaz of the Virginia Institute of Marine Sciences, who helped compile UNEP's findings on dead zones by reviewing global scientific journals, says the increase may be partly because of better scientific reporting. However, Diaz said "there's no mistaking the consistent upward trend over the last 50 years."

Diaz said the report was unable to estimate the total size of worldwide dead zones, but estimated the area to be roughly 300,000 square kilometers. While the vast majority of dead zones occur during fall and summer, some persist year-round, such as the Baltic Sea's 80,000-sq/km zone.

The UNEP report predicts that because rivers are dumping increasingly high volumes of nitrogen into oceans, dead zones will only worsen. However, paleoceanographer Kjell Nordberg of Goteborg University in Sweden says not all dead zones are caused by human activities, as climate and ocean conditions can cause hypoxia.

Nordberg says the dead zones that are a result of humans can be helped by placing restrictions on sewage discharge and agricultural practices, which can improve marine oxygen levels.

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