It is true that CO2 is soluble in water. As soon it come in contact with water molecules, it produce carbonic acid.
CO2 + H2O = H2CO3
Carbonic acid work on slightly or non soluble calcium and magnesium salt and make it soluble.
CaCO3 + HCO3 = Ca(HCO3)3
This is how alkalinity/pH is increased.
But how it increase ocean acidity. Or, this ocean acidity is a temporary phenomena?
To me, increase and decrease in oven pH is part of ocean ecology. Why it is presented is a problem?
Dear Nafees,
The first reaction that happens with carbonic acid H2CO3 is in most circumstances the conversion to HCO3- and CO32- which produces each a H+ ion, i.e. acidifies the ocean. The reactions are
H2CO3 HCO3- + H+ CO32- + 2 H+
and in the ocean, which has a pH of about 8, about 90% of all carbonic acid will end up in HCO3-.
But nevertheless, in principle, you are right that the reaction with minerals, such as CaCO3 will ultimately prevent or at least limit the decrease of pH. But it is important to notice that what you call 'temporary' is actually quite a long time; this is because the dissolution of CaCO3 in the large quantities that you need to counteract the atmospheric increase of CO2 happens mostly in deep-ocean sediments, which is a slow process.
A classical paper about the timescale that the reactions with CaCO3 take is
Archer, David, Haroon Kheshgi, and Ernst Maier‐Reimer. "Multiple timescales for neutralization of fossil fuel CO2." Geophysical Research Letters 24.4 (1997): 405-408.
which is freely available online. There are also newer summaries, e.g.
Archer, David, et al. "Atmospheric lifetime of fossil fuel carbon dioxide." Annual Review of Earth and Planetary Sciences 37 (2009).
I hope this helps.
Best regards, Christoph
The above question C is prepared in the light of this report.
http://www.climatecentral.org/gallery/graphics/ocean-acidification-more-co2-more-acidic
Dear Nafees,
The first reaction that happens with carbonic acid H2CO3 is in most circumstances the conversion to HCO3- and CO32- which produces each a H+ ion, i.e. acidifies the ocean. The reactions are
H2CO3 HCO3- + H+ CO32- + 2 H+
and in the ocean, which has a pH of about 8, about 90% of all carbonic acid will end up in HCO3-.
But nevertheless, in principle, you are right that the reaction with minerals, such as CaCO3 will ultimately prevent or at least limit the decrease of pH. But it is important to notice that what you call 'temporary' is actually quite a long time; this is because the dissolution of CaCO3 in the large quantities that you need to counteract the atmospheric increase of CO2 happens mostly in deep-ocean sediments, which is a slow process.
A classical paper about the timescale that the reactions with CaCO3 take is
Archer, David, Haroon Kheshgi, and Ernst Maier‐Reimer. "Multiple timescales for neutralization of fossil fuel CO2." Geophysical Research Letters 24.4 (1997): 405-408.
which is freely available online. There are also newer summaries, e.g.
Archer, David, et al. "Atmospheric lifetime of fossil fuel carbon dioxide." Annual Review of Earth and Planetary Sciences 37 (2009).
I hope this helps.
Best regards, Christoph
There is a full description, by top scientists from Wood Holes Oceanographic Institution, of the problem of ocean acidification here: http://www.whoi.edu/website/OCB-OA/faqs/oa-primer
Answer surely correct. But there is more. When a weak acid, carbonic acid, is dissolved together with a self salt, (Ca, Na)HCO3, it forms a buffer solution which forces pH, in this case, to nearly 6. How will the buffer property of carbonic acid work in the sea water? Any study available about it?
Second, deep ocean waters have already a low pH. How much influence this intrinsic low pH may have in the interpretation of CO2 as being thought to be the responsible?
Are all upwelling regions going to be ocean acidification hotspots? http://www.whoi.edu/OCB-OA/page.do?pid=112158
Basic: Some areas of the ocean undergo upwelling, which brings deep water to the surface. Because deep water carries more carbon dioxide than surface waters, it naturally has a lower pH. In some locations, like the west coast of the United States, upwelling water contains some CO2 from the atmosphere and some from respiration of organic matter falling from the surface ocean. These areas are ocean acidification “hotspots” where pH and saturation state are lower than usual. Not every upwelling site is guaranteed to be a hotspot, though. That depends on local circulation.
Upwelling areas are indeed regions of low pH. However, their water chemistry is set primarily by the rise of old deeper water, and not by anthropogenic CO2-driven ocean acidification. Deep water has naturally lower pH due to respiration of organic matter falling from the surface ocean. In some locations, such as off the west coast of North America (Feely et al. Science 2008), water upwelling from mid-depths contains a great deal of CO2 from respiration as well as from anthropogenic CO2, owing to local circulation, so that these locations demonstrate much lower pH and carbonate ion concentrations than are expected from upwelling or atmospheric CO2 invasion alone (Wootton et al. 2008). Seasonal upwelling happens in many locations worldwide. Upward movement of lower-pH, low-saturation state waters has been reported in the northeast Pacific Ocean (Feely et al. 1988 Marine Chemistry) and the Chukchi Sea in the Arctic Ocean as well (Bates et al 2009 JGR-Oceans)— S. Sundby, K.Y. Børsheim, S. Cooley
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