Download Terrigenous dissolved organic matter (DOM) is continuously

Introduction
Carbon is stored on our planet in the following major sinks: as organic molecules in
living and dead organisms found in the biosphere; as the carbon dioxide in the
atmosphere; as organic matter in soils; in the lithosphere as fossil fuels and sedimentary
rock deposits; and in the oceans as dissolved atmospheric carbon dioxide and as calcium
carbonate shells in marine organisms.
Sources for the Organic Matter:

Primary production (internal source): With water and energy from radiation from the
sun, phytoplankton use photosynthesis to convert carbon dioxide to carbon-based
sugar molecules. Through the metabolic addition of other elements these organism
produce more complex compounds like proteins, cellulose, and amino acids. Some of
the organic matter produced in plants is passed down to heterotrophic animals like
Zooplankton through consumption. It is then
o Released into the water as dead cells fecals or
o Broken down into CO2 by bacteria

River input (terrestrial or allochthonous): Dissolved organic matter (DOM) with
terrestrial origins is continuously discharged by rivers. The sources in freshwater are
plant and soil derived carbon, or rainwater leaching through organic soils, plant
debris. There are limitations of this input due to the so-called “salting out” effect.
This part is a poorly understood process regarding its distribution and reactivity in the
global carbon cycle.
Atmospheric input (allochthonous): at the interfacial layer humic substances (->
DOM, POM) and mono/polysaccharides and fatty acids are put into the water. This
process can be wet (rainwater, dissolved gases) or dry and is opposed by bursting
bubbles.
In more detailCO2 enters the ocean by diffusion. Once dissolved in seawater, the
carbon dioxide can remain as is or can be converted into carbonate (CO3--) or
bicarbonate (HCO3-). Coral, clams, some protozoa and some algae fix bicarbonate
with calcium (Ca++) to produce calcium carbonate (CaCO3 to produce shells and
other body parts. When they die, the shells and other things sink to the bottom where
they accumulate as carbonate-rich deposits. With time these deposits are altered into
sedimentary rocks under physical and chemical.

Excretion of Marine organism (internal source) as mentioned above


Resuspension from sediments, but mostly sediments are sinks (internal source)
Oil spills
Transformation of particulate organic matter in the ocean:
Soluble organic compounds are exuded or exretated by all marine organism, whereas
particulate organic compounds are formed from dead organism and fecal material. Only a
small fraction of the POM (particulate organic matter) reaches the seafloor and gets
buried, most of the POM is degraded and partially or completely decomposed during the
sinking, where they then can dissolve as DOM (dissolved organic matter). The difference
between DOM and POM is determined by the filtering size. POM on its way down, when
fully degraded in transformed into inorganic species, this process is called
remineralization.
Transformation of dissolved organic matter in the water, the sediments and soil:

DOM is – in general – labile and therefore quickly assimilated by bacteria. It follows,
that DOM is destroyed and remineralized into inorganic substances.
o Degradation is the process, where organic matter is broken down and maybe
its chemical complexity is reduced, whereas
o Decomposition is a chemical process, in which organic matter is completely
broken up into its constituents.
o And remineralization or regeneration is the dissolution of the hard parts, soft
parts or the degradation of POM that leads to soluble constituents, organic
matter is released to sustain primary production.

Through humification, which includes condensation, aggregation, oxidation and
reduction, DOM, which is low in molecular weight, is combined to form more inert
humic substances. Humic material aggregates and even “salt out” when binding
kations. Marine humic material is mostly formed in situ as result of biotic and abiotic
processes. Some humic material, for instance coastal humic material is introduced
from terrestrial sources, as described earlier on.
o Humification is the process that converts organic matter in the presence of
oxygen into humus. It is also called early diagenesis and happens soon after
the depostion of POM. It is the first step in the DOM transformation and very
fast and anaerobic. The difference between humification and early diagenesis
is that humification is more used for terrestrial settings and diagenesis for
marine or aquatic settings.
o Condensation is a chemical reaction in which union between to molecules is
involved. Often, simple molecules are eliminated the remaining compounds
often have a greater molecular weight.
o Polymerization: at least two molecules combine to a larger molecule with
repetitive structural units. In environmental settings no true polymerization
occurs, because there are not repeating monomer units.
o Oxidation means losing electrons.
o Aggregation refers to the clustering of molecules to form macromolecules or
colloidal species.

Fossilization of Carbonitrification occurs more slowly regarding geological time
scales. They are anaerobic processes, after organic matter was buried deeply into the
sediments or soil. It is an inorganic deposition of Carbon in the lithosphere.
o Fossilization or Maturation is a process when organic matter is transformed
into petroleum. It is initiated by diagenetic changes. The settings are anoxic
and temperatures less than 50EC.
o Carbonitrification is the transformation of organic materials in the partial
absence of air and high temperatures and pressures throughout geological time
into lignite and subsequently into coal. It is an anaerobic and occurs more
likely in terrestrial settings.

After burial in the sediments the organic matter undergoes biochemical degradation
and a couple of fossilization processes to finally form fossil fuels. These processes are
diagenesis, catagenesis and metagenesis, which include condensation, thermal
cracking and polymerization.
o Terrestrial environments:
Terrestrial plants contain lignin and cellulose, which are rather inert, relatively
depleted in hydrogen and upon maturation yield coal. After humification,
carbonitrification and carbonization fossil fuels are formed.
Carbonization is a form of fossilization and is typical for plants and insects.
When the volatile organic compounds disperse from a decomposing organism,
a black thin residue of carbon, originally part of the plant, is formed and left
behind. Lots of these organisms together make coal. It is an anaerobic process,
probably occurring in terrestrial settings.
o Marine and aquatic settings:
Plants in these environments contain a lot of lipids, which are hydrogen-rich,
and will yield gases and oils, upon maturation (diagenesis, catagenesis and
metagenesis). All of these are anoxic and occur probably in marine settings.
o Diagenesis: is the geochemical reaction occurring in the sediments
after the burial on timescales less then 1000years, conditions are
anoxic, and temperatures are between 0 and 50EC. Under these
extreme conditions extreme amounts of oxygen are removed by
bacterial (dehydration), denitrification occurs, sulfate is reduced,
methanogenesis happens and structures are rearranged. Kerogens are
built. This is an anoxic process occurring in marine settings.
o Catagenesis: is the geochemical reaction occurring in the sediments
after the burial on timescales greater then 1000years and at
temperatures between 50 and 150EC, which results in most gas and oil
o
o
o
o
production. The increased pressure and temperature cause cracking
reactions, where short-chain carbohydrates are broken off from larger
parent molecules. The kerogens are now transformed into
hydrocarbons like oil under decarboxylization, the process where
carbon dioxide is removed or eliminated from organic matter under
fossilization. It is an anoxic process and more likely to be seen in
marine environments.
Metagenesis: is the geochemical reaction occurring in the sediments
after the burial on timescales greater then one million years and
temperatures larger then 150EC. It is the last stage in the formation of
hydrocarbons. Temperatures are now the highest and the kerogen is
reorganized. Methane is produced from the cracking down of
hydrocarbon. This process is anoxic and is found in marine settings.
Dehydration describes the process of water loss from organic matter
under fossilization.
Demethanization describes the process of methane loss from organic
matter under fossilization.
Decarboxylization describes the process of carbon dioxide removal or
elimination from organic matter under fossilization.
The end
Carbon is released from ecosystems CO2 respiration involving the breakdown of carbonbased organic molecules into CO2. The detritus food chain contains a number of
organisms whose primary ecological role is the decomposition of organic matter into its
abiotic components. Sometimes volcanoes release CO2 that then enters the lithosphere,
when carbon-rich sediments are subducted and (partially) melted.