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Another consequence of global warming – ocean dead zones

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A panel discussion titled “Energy Choices and Global Warming” was held at the auditorium of the National Academy of Sciences on Sunday April 29. Jane Lubchenco, zoology professor at the University of Oregon, presented information on the impact of global climate change on the Earth’s oceans.

As the Earth warms, sea levels will rise and the salt content of the oceans will change as will the ability of the oceans to absorb carbon dioxide from the atmosphere. These changes will interact to affect atmospheric circulation, storm track, storm intensity frequency, and the frequency and distribution of droughts. The combination of sea level rise and harsher storms will more severely impact coastal communities and habitats.

The oceans are warming. Analysis of data from 1945 until 2000 from different oceans around the world shows a general increase in ocean temperatures. This has enormous consequences for many different plants, animals, and microbes that live in those ocean basins. “We only know some of the consequences that are underway.” One of the known consequences is that warmer water triggers the bleaching of coral which has increased in frequency and severity.

Satellite images from 1979 compared to 2000 show that the arctic ice is melting. Consequences of the melting arctic ice to many arctic species are likely to be severe. The impact will be felt by plants and animals as well as indigenous peoples. Polar bears are one example of an animal that is threatened because of changes to ice patterns impacting their ability to hunt seals.

Ocean conveyor belts could change as they have in the past. Ocean conveyor belts move heat around through the ocean basins affecting weather world wide. A change in the ocean conveyor belts is possible, but there is a “great uncertainty” if it will happen, but it is a great concern because if it were to happen it would have serious consequences to not only ecosystems but to people around the world.

About half of the carbon dioxide that has been put into the atmosphere by human activity has been absorbed by oceans. This absorption is making oceans more acidic. There is “good reason to be seriously concerned” because the rate a skeleton or shell is made or dissolved depends on the acidity of the water. Many of the animals and plants in the ocean will be challenged. Sea stars, sea urchins, mussels, clams, oysters, and corals are all impacted be ocean acidity.

These changes were all predicted – or recently discovered – such as ocean acidification. “The information we have from the last few years is suggesting that most of the changes that were predicted are changing at faster rates than expected.”

In addition to these predicted changes there are some “surprises” that were not predicted.

There are special areas in the oceans called coastal upwelling ecosystems. They are formed from a combination of geologic and weather conditions. Coastal upwellings compose 1% of ocean surface, but 20% of wild caught ocean fisheries and are therefore very important.

In these coastal upwellings nutrient rich colder waters are brought to the surface that feed the microorganisms which in turn feed the smaller fish and then up the food chain. Upwelling of nutrients is critical to these ecosystems. In recent years there have been significant deviations from the norm of upwelling in these areas.

Massive phytoplankton blooms are being observed. The consequence of the blooms combined with changes in wind patterns results in a zone of low oxygen. The water oxygen level gets so low it is insufficient oxygen for most animals and they suffocate and die. That area of the ocean becomes a dead zone.

This is type of ocean dead zone is different than other known ocean dead zones. Other ocean dead zones are as the result of run off of nutrients from the land. These new dead zones are a result of changes in coastal upwelling ecosystems. Photographs just off the coast of Oregon in 2000 show a rich assortment of animals. A photograph from the same area in 2006 only shows a massive numbers of dead crabs that had died from lack of oxygen – an ocean graveyard. The 2006 dead zone event lasted longer than previous dead zones reaching levels of zero oxygen.

It’s not clear if this has happened in the past – “we don’t know for sure”. However analyzing dissolved oxygen level records from 1950 to 1997 indicate that very low oxygen levels near the surface maybe something new although there are no records earlier than 60 years ago. Since this is a newly discovered phenomenon it can’t be said with certainty that it is climate related, but at this time it appears to be “most likely climate related.”

This same type of coastal upwelling dead zone is being observed off the coats of Chili, Peru, South Africa, and Morocco. “We think it’s likely that this new phenomenon in the most productive fishing waters is in fact likely to be related to climate change.”

Professor Lubchenco concluded, “The predicted impact and the surprises lend urgency to the call for reducing green house gas emissions.”

SOURCE: A panel discussion on "Energy Choices and Global Warming", Sunday April 29 2007, Jane Lubchenco, Zoology Professor at Oregon State University
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