[onsk (OP)]

I saw somewhere a list of things that may be effecting greenhouse gas shifts in the atmosphere, which included these two: rock weathering and ocean turnover. I am not sure what these are and how they may contribute to this process. An explanation would be most welcome.




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[frethack]

As for rock weathering, heightened rainfall and an expansion of the tropics/Hadley cell can increase the chemical breakdown of rocks, and very often the product is CO2 (especially in limestones).  If you have regions of uplift and mountain building, such as the Himalayas, often you will have an associated increase in relative atmospheric CO2 concentrations.

CO2 is mixed into the surface ocean, and then subducted to the deep ocean through the meridional overturning circulation in the N Atlantic that is fed by the Gulf Stream.  CO2 is also subducted from the Antarctic surface ocean when the Antarctic Bottom Water is formed.  A(n) decrease/increase in the amount of overturning circulation will decrease/increase the oceans ability to scrub CO2 from the atmosphere.  CO2 is generally scrubbed either by photosynthesis or carbonate precipitation.

Hope that helps a bit.

[SteveFish]

Dissolution in the ocean removes about 3/4 of added CO2 with variability depending upon the atmospheric concentration. The next biggest, but slow, removal is by reactions with CaCO3 or igneous rocks on land and in the ocean. On land, plants increase silicate weathering. If you want to learn more about removal of atmospheric CO2 by weathering, do a search for "silicate weathering CO2." For the actual research I suggest searching with Google Scholar and the RealClimate.org website has several articles by climate scientists that cover this topic. Steve

[onsk (OP)]

Thank you both very much for your enlightening information.

[GBO]

Rain water combines with CO2 to form H2CO3 carbonic acid.  More CO2 is scrubbed out by weathering of rocks forming bicarbonates and carbonate ions.  This is washed down to the ocean floor.

[CliffordK]

Rain water combines with CO₂ to form H₂CO₃ carbonic acid.  More CO₂ is scrubbed out by weathering of rocks forming bicarbonates and carbonate ions.  This is washed down to the ocean floor.

Yes, as I understood the "weathering" was actually removing Carbon Dioxide (CO₂) from the atmosphere.

Here is a good summary article:
http://www.karst.edu.cn/carbon/rockd.htm

combustion of fossil fuels releases about 5.4 billion tons of carbon a year as CO₂ into atmosphere. In addition, deforestation practices contribute about 1.6 billion tons of carbon a year to atmospheric CO₂. So, the total input of CO₂ from human activities is about 7.0 billion tons of carbon a year. However, only about 3.4 billion tons of carbon a year accumulates in the atmosphere. That means there is an atmospheric CO₂ sink of about 3.6 billion tons of carbon a year.

biggest carbon reservoir, carbonate rocks contain about 6.1x10⁷ billion tons of carbon, which is 1694 times and 1.1x10⁵ times larger than those of oceans and world vegetation respectively (Houghton & Woodwell, 1989). Carbonate rocks occupy an area of about 22 million square kilometers in the world (Yuan, 1997).

The basic reactions for carbonate rocks weathering can be expressed by:

  CaCO₃+CO₂+H₂O <----> Ca²⁺+2HCO₃^- for limestone

  CaMg(CO₃)₂ +2CO₂+2H₂O <---> Ca²⁺+Mg²⁺+4HCO₃^-  for dolomite.

So the "weathering" actually gives a net loss of CO₂, and is a mechanism by which the environment could sequester the excess CO₂ that we have been putting into the atmosphere without burying hydrocarbons (and making more coal/oil).

There are actually predictions by James Kasting that the "Weathering" could reduce the atmospheric carbon dioxide levels to lethal levels within 1/2 billion to 1 billion years.

It is predicted to actually increase with temperatures...  so I haven't seen the original data, but if we are able to maintain earth's temperatures through natural or artificial means, perhaps those estimates for longevity are low.