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Geology LibreTexts

3.3: The Lysocline and the CCD

[Fixed some minor typos/capitalization/grammar issues, edited to avoid use of first person plural]

[Problems found during readthrough:

-phenomena may not be the best word to explain what the lysocline and CCD are

-say what calcite and aragonite are, that organisms use them, etc. (unless that is in a previous section of this chapter)

-unsure whether saying 'supersaturated in calcite structures' is correct, since calcite is one form of solid calcium carbonate (not the ions dissolved in the water column)

-the sentences defining/explaining the lysocline need to be together in the paragraph.  Currently feels scattered/unclear.

-phrasing all of the bits about the mineral in terms of deposition and presence in the water column/on the seafloor as being either solid or aqueous might help with clarity -- phrases like 'calcite structures present' are somewhat vague and do not read smoothly

-'but below this exists the CCD' does not fit with the rest of this sentence and does not make clear what happens to carbonates between the lysocline and the CCD.

-did a little editing to clarify the bit about depths of the CCD in the Pacific v. the Atlantic, but the section still needs to be expanded to explain more thoroughly why/how these differences in chemistry affect carbonate solubility.  If the reasons for water chemistry differences in these two oceans have not been discussed already in an earlier chapter, summarizing this here will be important.

-the phrase 'issue in modern oceanography' sounds almost like the problem is only going to affect oceanographers and shouldn't be of concern to the average citizen...

-'tilted the carbon cycle' is not clear.  'Altered' might be a better word here than 'tilted.'

-the explanation of carbon equilibria is very choppy

-the carbon cycle should probably be explained before all of the info about the lysocline and CCD.  Doing this will make it possible to discuss ocean acidification more concisely.

-needs citations] [for some reason I can't insert this image without compromising the other image. But I think this is a good graph that should go here illustrating the lysocline and ccd]

The lysocline and carbonate compensation depth (CCD) are two phenomena that affect the stability of calcite and aragonite in the deep ocean. The lysocline is the depth at which the rate of dissolution of calcite begins to increase dramatically. The water above the lysocline is supersaturated in calcite structures (\(CaCO_3\)), but as depth and pressure increase and temperature decreases, the solubility of calcite increases. This continues until the lysocline is reached. The lysocline is the point where there is a dramatic decrease (up to 90%) in the amount of calcite structures present, but below this exists the CCD. At the CCD the rate of supply of calcite equals the rate of dissolution, and no more calcite is deposited below this depth. In the Pacific, this depth is about 4,5000 below the surface; in the Atlantic, it is about 6,000 m deep. This dramatic variation is due to differences in ocean chemistry. The Pacific has a lower pH and is colder than the Atlantic, so its lysocline and CCD are higher in the water column because the solubility of calcite increases in these conditions.

This is why ocean acidification is such a major issue in modern oceanography. Because of our constant burning of our fossil fuels following the industrial revolution, we have dramatically increased the amount of \(CO_2\) in our atmosphere and essentially tilted the carbon cycle. This tilting of the carbon cycle has thrown off the equilibrium between the atmosphere and the ocean. By increasing the amount of \(CO_2\) in the atmosphere we have also increased the amount of \(CO_2\) in the ocean. By increasing the \(CO_2\) in the ocean we are increasing the amount of H+ ions present.