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NSF Supports Proposal of ODU Chemists to Create a New Organic Carbon Analyzer

  • Kenneth Mopper
  • Aron Stubbins

Two Old Dominion University chemists have received funding from the National Science Foundation (NSF) to develop a highly sensitive instrument to measure organic carbon in seawater and give scientists a better understanding of the global carbon cycle.

Global warming, climate change and marine ecosystems are closely tied to the carbon cycle, providing a sense of urgency to the two-year project to be undertaken by Kenneth Mopper, professor, and Aron Stubbins, assistant professor, in ODU's Department of Chemistry and Biochemistry.

The title of the NSF grant is "Development of a High-Precision TOC/DOC Analyzer with a nM Detection Limit" and the amount is $394,749.

Total and dissolved organic carbon (TOC and DOC) in seawater are central components of the global carbon cycle, which is the process of carbon being cycled through the air, to plants, into animals, the ground, rivers, oceans and so forth. Organic carbon comes from living sources, such as the gigantic numbers of phytoplankton that take in carbon dioxide for photosynthesis as they grow on the surface of oceans, but then die, sink and decay.

Concentrations of carbon dioxide in the Earth's atmosphere have been increasing, much of it promoted by human activities such as the burning of fossil fuels. This is of major concern because carbon dioxide is a major greenhouse gas. Fossil fuels were created over millions of years as a result of dead organisms such as algae collecting on the ocean floor, being trapped in sediment and then being converted by heat and pressure into fossil fuels. So the burning releases ancient carbon of organic origin converting it carbon dioxide which is released to the atmosphere.

The dissolved organic carbon pool in the oceans is equivalent in size to that of the greenhouse gas, carbon dioxide in the atmosphere. Therefore any changes in the rates of the processes that convert DOC in the oceans to carbon dioxide in the atmosphere could accelerate ongoing climate warming. So precise measurement of organic carbon in the oceans is of great importance to scientists who are trying to establish how carbon-gain and carbon-loss processes are at work in the waters.

"Accurate measurements of these pools (of TOC and DOC) are needed for oceanic models, as well as for food web and climate-ocean feedback studies," Mopper said. "However, current DOC analyzers have problems in the analysis of seawater."

The main challenge is the minute quantity of DOC in open ocean waters. Such low concentrations make DOC incredibly hard to measure accurately, especially in the presence of the high salt content of seawater. Others problems are specifically tied to instrumental issues, such as the instability on research vessels at sea, or the salt deposits that can clog analyzer injection systems.

"The funded research project will explore the development of a new type of TOC/DOC analyzer that will potentially overcome these problems," Mopper said. "If the instrument is successfully developed, a number of major oceanographic and carbon cycling questions can be addressed."

The exact workings of the proposed instrument are secret because the scientists hope to commercialize it. But they do say their plan is to tweak the manner in which a seawater sample is purged of inorganic carbon, as well as the manner in which streams of the sample and reagent are mixed so as to yield a highly stable analytical signal. The results, they say, will be a nM (nanomolar) detection limit a thousand times more sensitive and precise than the limit of current analyzers.

"For the first time, ocean scientists would be able to accurately assess microbial respiration in the open ocean and thus help settle the controversy of whether the oceans are net autotrophic or net heterotrophic," Mopper explained.

Net autotrophic oceans would be dominated by primary producers, which are algae and any other organisms that can convert inorganic molecules-carbon dioxide, for example-into the molecules required for life. Algae gobble up carbon dioxide and keep it, at least temporarily in the waters, while they give off oxygen.

Heterotrophs, on the other hand, gobble up food previously produced by primary producers. They cannot produce their own food from inorganic sources. This category includes humans, but in the oceans is dominated by bacteria that feast on the dissolved organic carbon produced by the algae. In surface waters, most heterotrophs utilize aerobic respiration, meaning they take in oxygen to "burn" the fuel of DOC and give off carbon dioxide.

Because the world's oceans hold as much DOC as there is carbon dioxide in the atmosphere, any changes in the balance could be bad for the environment. For example, a drop-off in phytoplankton productivity could limit the ability of the oceans to extract carbon dioxide from the atmosphere. Whereas an increase in bacterial respiration would eat away at current stocks of DOC, releasing them to the atmosphere as carbon dioxide.

Mopper said the new instrument could provide measurements that allow scientists to keep closer tabs on this primary production of basic food-web organisms in the open oceans. "Oceanic primary productivity and respiration are critical processes in the global carbon cycle. Small shifts in these rates could cause major shifts in the amount of carbon dioxide in the atmosphere. The instrument to be built with this grant will finally allow these rates to be measured accurately."

He added that potential nonmarine applications would include monitoring low-level organic carbon in power plant cooling water, boiler feed water, high-purity water generating systems, drinking water, sterilized water used in manufacturing and a variety of regulatory monitoring operations.

Development of the instrument will be supervised by Mopper, but he said that Stubbins would be responsible for most of the day-to-day work. "We may hire an engineer to help develop the instrument, but we are not sure at this point," Mopper said.

Mopper, whose Ph.D. is from a joint program of MIT and Woods Hole Oceanographic Institution, joined ODU in 2000. He worked on a previous NSF-supported project that led to the development of a commercial total organic carbon analyzer. His research areas also include the study of the impact of photochemical processes on oceanic and global carbon cycling; the study of free radicals and stable photoproducts and their reactions in natural waters; the characterization of humic substances in natural waters; and the development of analytical techniques for trace organics, TOC and DOC and photochemically formed species in natural waters.

Stubbins, whose doctorate in marine biogeochemistry is from the University of Newcastle-upon-Tyne in Great Britain, joined ODU in 2005. In addition to working with Mopper, he has served with Patrick Hatcher, the university's Batten Endowed Chair in Physical Sciences, as a leader of the Virginia Coastal Energy Research Consortium.

In 2007, Stubbins received his first NSF grant, this one for $465,000, for a sophisticated new study of dissolved organic matter in seawater. Hatcher, Mopper and Jingdong Mao, assistant professor of chemistry and biochemistry, are working with him on that project.

Overall research focuses for Stubbins include photochemical and biological rates of conversion between organic carbon pools and the atmospheric pool of carbon dioxide. He has studies ongoing in the Atlantic Ocean near Cape Verde, the Pacific Ocean near Hawaii, at Yukon and Alaskan glaciers and in the Congo River of equatorial West Africa.

This article was posted on: August 13, 2009

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