Costa Rica Reciclaje | Reciclar Aluminio | Reciclar Plastico | Reciclar Papel | Reciclar Carton | Reciclar Latas | Reciclar Basura | Basura Reciclaje | Material Reciclaje

Español » English

Recycling Guide

  • First: All kinds of papers.
  • Second: Cans and bottles that have been rinsed.
  • Third: Biodegradables, such as fruit peels and vegetables that can be used as organic composite.
  • Fourth: Non-recyclables.

Ocean Dead Zones Growing;
May Be Linked to Warming

Article By National Geographic - http://www.news.nationalgeographic.com

Researchers have tracked a decline in dissolved oxygen levels since 1960 in the tropical Pacific and Atlantic Oceans, which has extended the size of these undersea deserts and intensified their effects.

The oxygen level in these zones "is below the critical oxygen level for fish and other large marine animals," said team leader Lothar Stramma, of the Leibniz Institute of Marine Sciences at the University of Kiel in Germany.

The team constructed a time line of oxygen concentrations at depths of between 985 and 2,295 feet (300 and 700 meters) using oxygen data records going back 50 years. The results fit predictions of the effects of global warming.

The world's hypoxic zones—swaths of ocean too oxygen-deprived to support fish and other marine organisms—are rapidly expanding as sea temperatures rise, a new study suggests.

The study team notes that seas have warmed substantially over the past 50 years and that climate models predict falling levels of oceanic oxygen in response to global warming.

Underwater Deserts

The study team suspects these underwater deserts are also spreading horizontally to cover wider areas of ocean, though more research is needed. "We think there are areas that are extending, but we don't have the maps to show that right now," Stramma said.

Rising temperatures can prevent oxygen-rich surface waters from circulating to lower depths, since water becomes less dense as it warms, Stramma explained.

"Then you have less ventilated water for deep and middle layers, which means you have less oxygen supply from the surface," he said. "That is a problem for the larger fish, which need a lot of energy."

Commercial fisheries, particularly in the tropical east Atlantic, could suffer, he added.

"This is an area where there are a lot of tunas," Stramma said. To feed, "bigeye tuna go quite deep to 250 meters [850 feet], so for these guys the area where they live reduces.

Hypoxic zones also severely reduce overall biological productivity, which reverberates throughout the food chain, he said.

Other recent studies have also noted a long-term trend of falling oxygen levels in non-tropical seas. In the sub-Arctic Pacific, for instance, reduced oxygen concentrations have been reported at depths of 330 to 1,310 feet (100 to 400 meters) between 1956 and 2006.

Past Episodes

While the new study suggests human-caused global warming as a possible cause, the team notes that oxygen-deprived seas aren't a new phenomenon.

Paleontological records show that Earth has experienced episodes of much more severe ocean suffocation in its past.

For instance, drastically reduced oxygen levels linked to an era of global warming marked the planet's worst ever extinction event: the end of the Permian period 251 million years ago, when more than 90 percent of all marine species were wiped out.

Today, however, other factors may be amplifying the effects of global warming in spurring the growth of tropical hypoxic zones, said Thomas Wagner, professor of earth systems science at Newcastle University, U.K.

Local human impacts due to land use changes may contribute to the effects highlighted in the new study, he said.

"If you warm up the atmosphere, at the same time you increase the activity of water in the atmosphere," which in turn leads to increased rainfall and river flows into tropical coastal waters, Wagner said.

These flows contain organic runoff such as agricultural fertilizers and sewage, fueling algal blooms that consume the oxygen in seas, he said.

"This is a second mechanism which may also have an impact on [oceanic] oxygenation in certain areas," he said.

"Many mechanisms can play together, and it's very difficult to identify which is the leading one," he added. "I think we are still far away from being really confident of how an ocean system will respond [to global warming]."