'Cooking Reaction' at the Seabed may have Stored Millions of Tonnes of Carbon

Switch on the stove burner, put a cooking pan, add some oil and then add the stuff you want to cook- be it fresh green vegetables or pieces of meat or fish. The food changes gradually until it turns brilliant brown, adding the typical flavour. Culinary involves, without our knowledge, breaking of bonds of molecules and changing them to other simpler forms through chemical reactions. 

A famous reaction in cooking is the Maillard Reaction—the chemical process through which browned foods get their typical flavour. Malliard reaction involves reducing sugars reacting with amino acids (from proteins in the food) at high temperatures (which we put from the burner), forming a complex mixture of compounds, the melanoidin. It was named after Louis Camille Maillard, who first described it in 1912. 

Now, Researchers have found that the Malliard reaction can occur at the seabed and plays an important role in trapping organic carbon, thus reducing carbon dioxide release to the atmosphere and protecting early life. The research has been published recently in Nature. 

Marine organic carbon is an important component of the global carbon cycle, the natural way of reusing carbon atoms. Remember, carbon is the primary chemical in all of Earth's life. 

The total amount of carbon on our planet remains constant; that is, the carbon we have at present is the same that we have always had. In living organisms, carbon forms the biological backbones—proteins and DNA (and RNA). The carbon cycle determines the path of carbon—from the atmosphere to organisms and back to the atmosphere. Organic carbons in marine sediments play a crucial role in a wide range of phenomena, including carbon sequestration. 

Deaths of microorganisms primarily contribute to the organic carbons in the oceans. When these organisms die, they sink to the bottom and start decaying, a process that uses oxygen and releases carbon dioxide. The carbon dioxide released into the ocean as such finally comes to the surface of the ocean and then enters the atmosphere. 

Researchers think the other way. Can some organic carbon be captured or preserved in the sediments? Milliard equation became a possibility as it converts carbon into larger complex molecules (remember what happens in cooking). The larger molecules are not easily broken down and hence remain in the sediment. 

The researchers of the Nature paper wrote, "The preservation of organic carbon (OC) in marine sediments over geological time requires that OC escapes microbial remineralisation that otherwise converts it into dissolved inorganic carbon and/or carbon dioxide. This premise is central to all OC preservation mechanisms and requires that OC is either inherently stable or is made stable against microbial breakdown."

From this, we can judge what the researchers had in their minds— the question of whether organic carbon is saved from microbial degradation and stored in the ocean sediment. Searching for the possibility of the Maillard reaction being involved started decades back. It is known that the Maillard reaction takes place in ocean sediment. But the temperature at the seabed is not that high for this reaction to occur smoothly. 

The new research searched for the involvement of minerals in it that can catalyse the reaction. In the study, they found that iron and manganese, available in seawater, can catalyse the Maillard reaction by two orders of magnitude at the temperature of the seabed. 

Oliver Moore, the lead author of the study and a research fellow at the School of Earth and Environment, University of Leeds, UK, in a statement quoted in the University release, said, "It had been suggested back in the 1970s that the Maillard reaction might occur in marine sediments, but the process was thought to be too slow to impact the conditions that exist on Earth. Our experiments have shown that in the presence of key elements, namely iron and manganese, which are found in seawater, the reaction rate is increased by tens of times."

Moore added, "Over Earth's long history, this may have helped create the conditions necessary for complex life to inhabit the Earth."

The speeding up of the Maillard reaction by the mineral catalysts like iron and manganese could have stored four million of carbon in the seabed each year, which otherwise would have been released into the atmosphere, the researchers estimated. 

The researchers incubated organic molecules with iron and manganese in different forms under conditions that mimicked the seabed. The reactive forms of iron and manganese, the researchers found, catalysed the Maillard reaction up to two orders of magnitude. 

However, other experts have some cautionary messages as well. In an article about the findings, written by Julia Robinson at Chemistry World, David Burdige, a marine geochemistry expert, urged to be careful in determining the amount of carbon the Maillard reaction had locked at the seabed. 

Burdige, in the same article, however, said, "But I think this is a good first start – it points out a unique twist on processes that could be important that hasn't been fully explored. Moore's team is postulating that this is a potentially important mechanism that has been underappreciated, and I think they're absolutely right."