Refractory carbon: Managing climate change, or making it worse?

Dissolved organic carbon (DOC) is a key component in the marine microbial life cycle. It promotes growth and is used as a major source of energy for many heterotrophic bacteria. By contrast, refractory dissolved organic carbon (RDOC) is an inedible by-product that cannot be utilised. The role of RDOC has not been studied with great depth and its origins largely unknown although contributions include when organic matter is degraded by light at the surface and oil seeps such as the spill in the Gulf of Mexico. Microbes are also a key player in the conversion of bioavailable carbon in refractory carbon learned by a study done in 2001 by Ogawa. He theorised that microbes can alter the structural composition of the labile DOC which fixes it into RDOC. The peptidoglycan structure is changed so the polysaccharide component is no longer recognisable at the molecular level. Degradation of matter occurs due to enzymatic activity so RDOC could potentially have such an altered biochemical structure that degradation enzymes cannot bind to any active sites, thus preventing degradation on any level.

Theories also persist about the potential of the RDOC in managing climate change. Due to the massive amounts of atmospheric carbon being produced, resulting in increased acidity of the ocean, could this not be an adequate response to prevent such disastrous alterations?  By effectively sequestering carbon, it is almost preventing a potentially worldwide change in the oceans and the atmosphere. Such studies have included seeding the ocean with iron fertiliser which stimulates phytoplankton blooms and sucks carbon dioxide out of the atmosphere. A higher concentration of carbon in the ocean could potentially cause a higher amount of carbon becoming refractory, thus taking it out of play in the carbon cycle. Nagappah Ramaiah also points out that there are approximately 35-40 micromoles of refractory carbon per litre of seawater. An increase of a mere 2-3 micromoles would result in several billion tonnes of refractory carbon being added to the pool. Although there is some worry that this could backfire and exacerbate the problem. Meinhard Simon poses the infeasibility of the potential of sequestering excess carbon due to having no handle on any controls.

The dangers are potentially quite damaging as the amount of RDOC in the water column rivals the amount of atmospheric carbon reported by Jiao. This reservoir of untapped carbon would effectively double the amount of carbon in the atmosphere if released.
Though this would be dependent on how quickly, if at all, this carbon would be released. Over a long period of time, the effects would most likely be so gradual it would hardly be noticed, similarly to pre-industrial carbon amounts versus today. However, released in a relatively short space of time could cause catastrophic alterations to the global carbon cycle. This could result in major increased acidity of the oceans and increased carbon dioxide concentration in the atmosphere. This could trigger a knock on effect with global warming due to thawing of approximately 1,672 billion tonnes of locked carbon in the permafrost (earthobservatory.nasa.gov). So there are definitely valid arguments against tampering with this inaccessible pool of carbon and until more studies are done maybe it is best to leave well enough alone for the mean time. 

References

Jiao, N,  Azam, F., Sanders, S. (2012) Microbial Carbon Pump in the Ocean. American Association for the Advancement of Science. Online: http://www.sciencemag.org/site/products/microbialpump/ Accessed 9/12/2014 (CBM)

http://www.sciencemag.org/site/products/scor_aaas.pdf

http://earthobservatory.nasa.gov/Features/CarbonCycle/page5.php