Does this mean that aragonite can dissolve every time our pH dips?

[mcarroll]

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2011JC007599
"The solubility of Fish Produced High Magnesium Calcite in Seawater"

Does that graph depict aragonite dissolving at an increasing rate as pH drops <8.0?

Is there a table or graph somewhere that shows this better? I've been looking and so far this is all I've come up with. (Interesting parent article tho!)

 

[Randy Holmes-Farley Verified Community Expert]

I don’t know what that graph is exactly, but you need to be below pH 7.7 in seawater at 7 dKH to dissolve aragonite, and unless the pH is well below, the dissolution is very slow.

The supersaturation of aragonite is seawater is very well known.

 

[mcarroll]

I don’t know what that graph is exactly, but you need to be below pH 7.7 in seawater at 7 dKH to dissolve aragonite, and unless the pH is well below, the dissolution is very slow.

The supersaturation of aragonite is seawater is very well known.

The whole article is online, so I was hoping the context would help with the chart. The figure is titled "Aragonite solubility in seawater." and Millero is one of the article authors.

Regardless, I'm trying to find that info in a chart or table form, if possible. Was hoping to find it in Millero's Chemical Oceanography, but not finding anything exactly showing aragnite vs pH.

Any suggestions?

 

[mcarroll]

One figure (I thiink I saw in Millero) shows AΩ vs pH.

AΩ is the "aragonite solubility coefficient", but I'm not sure how to interpret that....it's a decreasing value as pH decreases.

 

[mcarroll]

https://oceanbites.org/is-aragonite-saturation-state-ωa-the-best-to-describe-calcification-rate/

If Ωa > 1, seawater is supersaturated with respect to calcium carbonate (CaCO3) and conditions are favorable for CaCO3 precipitation, the process necessary to form corals; conversely, if Ωa < 1, seawater is undersaturated with respect to CaCO3 and the dissolution of CaCO3 is favored.

Does this accurately explain the X-axis of the graph I posted? Trending toward 0.00 as pH falls to ~7.6 (as on the graph) sounds about like what you described. Solubility increasing along the way.
(Another interesting read, too.)

 

[Randy Holmes-Farley Verified Community Expert]

One figure (I thiink I saw in Millero) shows AΩ vs pH.

AΩ is the "aragonite solubility coefficient", but I'm not sure how to interpret that....it's a decreasing value as pH decreases.

If omega is less than 1, the chemical can dissolve. The lower it is, the faster dissolution can be. If omega is 1 or higher, it cannot dissolve and may precipitate.

For aragonite, omega drops to 1 in seawater around pH 7.7.

 

[mcarroll]

That all helps – thanks!