Oxygen cycle

The term oxygen circulation or oxygen cycle is defined as the transport and storage of oxygen in the atmosphere, biosphere and lithosphere. This cycle is a biogeochemical cycle. The main driving factor of the oxygen cycle is photosynthesis, which is responsible for the modern Earth's atmosphere (see Large oxygen catastrophe ). The oxygen cycle is connected by oxidations and reductions with the other biogeochemical cycles. These run with many other elements because of the high reactivity of oxygen particularly rapidly.

Memory

The largest of the Earth 's oxygen storage in the silicate and oxide minerals of the earth's crust and mantle (99.5 %). Only a small part is released as free oxygen to the biosphere (0.01%) and the atmosphere (0.36 %). The main source of atmospheric free oxygen is produced in photosynthesis, free oxygen from water:

Photosynthetic ( photoautotrophic ) organisms are primarily plants, especially the land plants and phytoplankton in the oceans. In addition, there photoautotrophic bacteria and archaea. The tiny marine cyanobacterium Prochlorococcus is blamed for example, more than half of the photosynthesis of the open ocean. It was not discovered until 1986.

An additional source of free atmospheric oxygen is the photolysis, wherein the high -energy ultraviolet radiation, atmospheric water and nitrous oxide breaks into atoms. The free H- and N- atoms ( radicals) in the atmosphere to react with other compounds, or the hydrogen to escape in the space:

Free oxygen can disappear from the atmosphere by respiration and decay mechanisms in which heterotrophic organisms such as Animals and bacteria consume oxygen and release carbon dioxide.

The lithosphere also consumes free oxygen by chemical weathering and surface reactions. An example is the formation of iron oxide ( rust):

Capacities and rivers

The following tables show the estimated oxygen storage and circulation flows.

Table 1: Important reservoir, which are involved in the oxygen cycle:

Table 2: Annual gains and losses of atmospheric oxygen (units of 1010 kg O2 per year):

Ozone - oxygen cycle

The presence of atmospheric oxygen led to the formation of ozone (O3 ) and the ozone layer in the stratosphere. The ozone layer is very important as it absorbs the harmful UV radiations: