Talk:Oxygen cycle
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Why no hydrosphere? Just wondering why the overview paragraph and the image make no reference to the hydrosphere. Surely this is a significant resevoir for oxygen given that there is dissolved O2 and CO2 and there is H2O itself. - Drstuey 07:28, 22 Nov 2004 (UTC)
Answer: I decided not to differentiate between the hydrosphere and biosphere, mainly because I didn't have enough info to break down the biosphere reservoir into land surface and hydrosphere components. Also, dissolved O2 levels in the hydrosphere are a function of biologic activity. For an interesting theory on the relationship between the evolution of photosynthetic life, dissolved oxygen in the ocea, and the worlds main commercial source of iron, check out the banded iron formation. - Cbusch01 14:46, 13 Jul 2005 (MST)
Watson/Lenton
As I am researching the subject of what regulates the oxygen content of the atmosphere, I have found the works of professor Watson and dr Lenton at East Anglia University ( see here: http://www.uea.ac.uk/~ajw/pubs.htm , particular the pieces that have Redfield Revisited in their title). It is not easy stuff (as I am but a humble journalist), but what I have understood so far is that the oxygen production by photosynthesis is a netto neutral affair, in that all the oxygen produced by trees shrubs and plankton is consumed by the breakdown of these organisms. So there must be other oxygen sources and if I understand Watson/Lenton well then one of these sources is the chemical weathering of rocks by plantroots that releases oxygen in the atmosphere and the burial of marine life in geologic time that once produced oxygen but which was buried without reclaiming the produced oxygen back. Bu~t I would be very happy to see on the Wiki page how you interpret this. Thanks
Theo Richel (www.richel.org/resume) 82.176.201.176 09:52, 30 November 2006 (UTC)
Answer: The amount of "free" oxygen in the atmosphere is dominated by photosynthesis. By free oxygen I mean that in the form of O2 gas. It is true that all the oxygen produced by photosynthesis is eventually consumed by respiration and decay, but there is a lag between when it is produced and when it is consumed that allows it to remain in the atmosphere for a period of time. A good analogy for atmospheric oxygen is a stream-fed lake. Initially, the flow of water into the lake bed is greater than the flow out and the lake slowly fills up with water. Eventually the water level in the lake is high enough that the routes of escape for water can keep up with the incoming stream, thus reaching the point that the inflow and outflow are in equilibrium (the netto neutral affair you mentioned). Although the lake level is now static, it is still filled with water. In the same manner, the oxygen "lake" in the atmosphere is still full even though the level is basically static. If the photosysntesis stream were ever turned off, the free oxygen "lake" would eventually dry up. But here is the tricky part: the oxygen molecules would still remain in the atmosphere. However, instead of being in the form of free oxygen (O2), it would be converted to carbon dioxide (CO2) via respiration and decay. Without photosynthesis, the planet earth would have a nitrogen/carbon dioxide atmosphere instead of the nitrogen/oxygen atmosphere we currently enjoy. There are other sources of atmospheric free oxygen instead of photosynthesis, but these other sources produce so little oxygen that they are virtually insignificant in the big picture. By-the-way, the main source of carbon dioxide and nitrogen in the atmosphere is volcanoes. See the carbon cycle and nitrogen cycle articles for further discussion. - Cbusch01 09:23, 07 May 2008 (CST)
