Generation hypothesis of persistent organic matter

In "Dynamics of Marine Life Systems 3 Chain of Marine Organisms" (Kazuhiro Kogure [ed.] Tokai University Press), based on the latest research results, he describes the hypothesis of the generation of persistent organic matter in the ocean. increase.

The author (Ohki) interprets marine life system dynamics ③ and draws a diagram.

　Prokaryotic bacteria are the smallest of the organisms' particulate organic matter POMs. When this dies and the decomposition progresses a little and becomes finer, it immediately shifts to the dissolved fraction DOM. Some bacteria feed on DOM. The growth of such bacteria will cause the DOM to revert to POM.

　When examining the composition of persistent organic matter in seawater, many fragments of membrane components of microorganisms were found. Since it is a membrane that protects living cells, it must have a structure that is difficult to decompose.When microorganisms (bacteria, etc.) die and undergo decomposition, membrane-derived components are fragmented. When monomers (saccharides and phenols) repeat polymerization to polymerize, it is thought that they become persistent macromolecular organic substances.

　It has also been confirmed that persistent organic matter is generated when microorganisms decompose organic matter in seawater. The genesis of persistent organic matter is currently a topic of intense research. 

　Phenols (benzene ring-OH) absorb visible light. Polymeric organic substances polymerized with phenols are characterized by their dark brown color. It is called a colored DOM or a chromophoric DOM because it is an organic matter that has color, and is called a C-DOM. It also has a "fluorescent property" that emits light of a different wavelength when it absorbs light. This is called fluorescent dissolved organic matter (Fluorescent DOM: FDOM). Taking advantage of this characteristic, we irradiate seawater with UV-A (excitation light) with a wavelength of 320 nm and define humus-like substances that emit fluorescence with a violet wavelength of 420 nm. The higher the fluorescence intensity, the greater the amount of humus-like substances. The distribution of humus-like substances has been investigated by examining the fluorescence intensity of seawater.

　Much of the dissolved organic matter in the ocean is persistent. Persistent organic matter decomposes gradually over an average of thousands of years. It is believed that some are degraded by microorganisms and some are photodegraded on the ocean surface. A theory has also been proposed that a part of the persistent organic matter turns into gas when it undergoes photodecomposition.