Methane loss under coastal deoxygenation over the southwest coast of India

What is it about?

Methane is a second potent greenhouse gas, next to nitrous oxide and carbon dioxide, that is being added to the atmosphere through both natural processes and human activities. One of the most important factors that control biogeochemical cycling of methane is the redox state of the environment, which is primarily determined by the ambient oxygen concentration. Contrary to the general belief that the oxygen depleted environments support high concentrations of methane, we observed significant reduction in methane concentrations over the southeastern Arabian Sea (SEAS) shelf when upwelling driven oxygen depleted conditions prevailed. Although methane exhibited high concentrations under oxic conditions due to its greater sediment-water diffusion caused by the large size organisms living in the sediments, such biological activities are restricted to a greater extent due to the avoidance of larger animals under deoxygenated conditions. The methane thus retained in the sediment may undergo microbially-mediated oxidation thereby its sea to air emission is reduced significantly.

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Why is it important?

It is important to note that the periods of intense upwelling and oxygen depletion over SEAS are also happened to be the largest source of carbon dioxide, so the potential net impact of greenhouse gases carries significant importance for this region.