Aquatic 'dead zones' contributing to climate change

March 11, 2010, University of Maryland

The increased frequency and intensity of oxygen-deprived "dead zones" along the world's coasts can negatively impact environmental conditions in far more than just local waters. In the March 12 edition of the journal Science, University of Maryland Center for Environmental Science oceanographer Dr. Lou Codispoti explains that the increased amount of nitrous oxide (N2O) produced in low-oxygen (hypoxic) waters can elevate concentrations in the atmosphere, further exacerbating the impacts of global warming and contributing to ozone "holes" that cause an increase in our exposure to harmful UV radiation.

"As the volume of hypoxic waters move towards the sea surface and expands along our coasts, their ability to produce the nitrous oxide increases," explains Dr. Codispoti of the UMCES Horn Point Laboratory. "With low-oxygen waters currently producing about half of the ocean's net nitrous oxide, we could see an additional significant atmospheric increase if these 'dead zones' continue to expand."

Although present in minute concentrations in Earth's atmosphere, nitrous oxide is a highly and is becoming a key factor in stratospheric . For the past 400,000 years, changes in atmospheric N2O appear to have roughly paralleled changes in carbon dioxide CO2 and have had modest impacts on climate, but this may change. Just as human activities may be causing an unprecedented rise in the terrestrial N2O sources, marine N2O production may also rise substantially as a result of , warming waters and . Because the marine environment is a net producer of N2O, much of this production will be lost to the atmosphere, thus further intensifying its climatic impact.

Increased N2O production occurs as dissolved oxygen levels decline. Under well-oxygenated conditions, microbes produce N2O at low rates. But at oxygen concentrations decrease to hypoxic levels, these waters can increase their production of N2O.

N2O production rates are particularly high in shallow suboxic and hypoxic waters because respiration and biological turnover rates are higher near the sunlit waters where phytoplankton produce the fuel for respiration.

When suboxic waters (oxygen essentially absent) occur at depths of less than 300 feet, the combination of high respiration rates, and the peculiarities of a process called denitrification can cause N2O production rates to be 10,000 times higher than the average for the open ocean. The future of marine N2O production depends critically on what will happen to the roughly ten percent of the ocean volume that is hypoxic and suboxic.

"Nitrous oxide data from many coastal zones that contain low oxygen waters are sparse, including Chesapeake Bay," said Dr. Codispoti. "We should intensify our observations of the relationship between low oxygen concentrations and nitrous oxide in coastal waters."

Explore further: Nitrous oxide from ocean microbes

More information: The article "Interesting Times for Nitrous Oxide" appears in the March 12, 2010 edition of the journal Science.

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1 / 5 (3) Mar 12, 2010
This so scary!

Yet, are we sure about the facts in this article?

For the life of me, I cannot see how the strip (or ribbon) of the ocean, lapping the continental shelves, that is up to 300 feet deep, can comprise 10 percent of the volume of the ocean!

What am I missing?
1 / 5 (1) Mar 12, 2010
Nitrous Oxide you say? Well, that certainly helps explain the peculiar behavior of the coastal areas of the US, say for example Washington DC or anywhere in California, Texas. I think it's safe to say the middle of the country looks at those regions as a little bit wobbly. Good ol' Nitrous, that explains a lot of the last 25 years.
1 / 5 (4) Mar 12, 2010
Nitrous oxide is a good gas, without it plants would die, personally I would like to see our atmosphere with a lot more N2O and CO2, help the crops in our compound while we wait for the bringers of the real constitution :)
1 / 5 (1) Mar 13, 2010
Nitrous oxide has been rising linearly since consistent measurements started in 1985. Hasn't increased, hasn't decreased. Straight line.

Meanwhile, as this article states, the dead zones have been happening with "increased frequency and intensity".

What's wrong with this picture? If it were a real threat we would have seen it in the observations ... but then, climate scientists don't do observations these days.

"Science" Magazine sinks to a new low ...
5 / 5 (1) Mar 13, 2010
Actually nitrous oxide has gone up from 300 ppb to 320 ppb from 1975 to 2005.

Please see the chart:

Figure 3 Nitrous Oxide


Atmospheric Concentrations of Greenhouse Gases in Geological Time and in Recent Years

Given the fact that the radiative forcing is roughly proportional to the square root of the concentration for nitrous oxide (whereas the forcing due to water vapor and carbon dioxide is proportional to the logarithm of their respective concentrations) the forcing due to nitrous oxide is more sensitive to concentration.

Please see:

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